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Electronic requirements and stereochemistry of nucleophilic-induced rearrangement-displacements of (halomethyl)silanes

Allen, John Michael, III, Ph.D.

The Ohio State University, 1991

UMI 300 N. Zeeb Rd. Ann Arbor, MI 48106

ELECTRONIC REQUIREMENTS AND STEREOCHEMISTRY OF NUCLEOPHILIC INDUCED REARRANGEMENT- DISPLACEMENTS OF (HALOMETHYL)SILANES

DISSERTATION

Presented in Partial Fulfillment of the Requirements for

the Degree Doctor of Philosophy in the Graduate

School of The Ohio State University

b y

John Michael Allen III, B.S.

The Ohio State University

1991

Dissertation Committee: Approved by Dr. Gideon Fraenkel Dr. Harold Shechter Dr. John Swenton Dr. Donald Witiak Advisor Department of Chemistry ACKNOWLEDGEMENTS

I thank the members of Professor Harold Shechter's research group who I have been associated with through the years and especially Dr. Harold Shechter for his patience and advise (especially these last few months). VITA

January 7, 1963 Born - North Tonawanda, New York

1985 . . B. S. , Niagara University

1985 - 1987 . Graduate Teaching Associate Department of Chemistry The Ohio State University, Columbus, Ohio

1987 - Present Graduate Research Associate Department of Chemistry The Ohio State University, Columbus, Ohio

FIELD OF STUDY

Major Field: Chemistry

Study of Organic Chemistry under the guidance of Professor Harold Shechter. TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

VITA iii

LIST OF TABLES ‘ v

LIST OF FIGURES vii

CHAPTER

I. Statement of Problem 1

II. Historical 4

III. Preparation and Reactions of Aryl(halomethyl)- diphenylsilanes 24

IV. Discussion of Migratory Aptitudes 53

V. Stereochemistry of Rearrangement-Displacements 59

VI. Summary 86

VII. Experimental 88

REFERENCES 145

iv LIST OF TABLES

Table Page

1. Displacement Reactions of (Chloromethyl)trimethylsilane (12) with Various Nucleophiles.

2 . Products (% Yield) of Reactions of Aryl(chloromethyl)- dimethylsilanes (12) with Sodium Ethoxide in Ethanol. 10

3. Product Distributions (% Yield) for Reactions of 20 with Sodium Methoxide in Varied Solvents 12

4. Migratory Aptitudes (Ar/Ph) for Reactions of 22. with Fluoride Ion at 0 °C in Tetrahydrofuran 21

5. Statistically Corrected Relative Migratory Aptitudes and Sigma-zero Values for Reactions of para-Aryl(bromomethyl)diphenylsilanes (4a-f) with Tetrabutylammonium Fluoride at 23 °C. 32

6 . Statistically Corrected Relative Migratory Aptitudes (p-Z-Ph/Ph) in Reactions of Aryl(bromomethyl)- diphenylsilanes (4a-f) with Fluoride Ion at 0 °C and -20 o c . 36

7. Statistically Corrected Relative Migratory Aptitudes (p-Z-Ph/Ph) in Reactions of Aryl(iodomethyl)diphenylsilanes (5a-f) with Fluoride Ion at 23 °C. 40

8 . Statistically Corrected Relative Migratory Aptitudes (p -Z-Ph/Ph) in Reactions of Aryl(bromomethyl)- diphenylsilanes (4a-f) with Methoxide Ion at 23 °C 45

v LIST OF TABLES (cont.)

Table PAGE

9. The Effects of Solvents on the Migratory Aptitudes for Rearrangement-Displacements of 4f with Fluoride and Methoxide Ions at 23 °C. 48

10. Corrected Migratory Aptitudes for Rearrangement- Displacements of 4f and 4Ji at Varied Concentrations of Fluoride Ion. 49

11. Corrected Migratory Aptitudes for Fluoride-Induced Rearrangement-Displacements under Varied Conditions of 4f. 52

12. The Stereochemistry of Substitution Reactions of Chiral Methyl(l-naphthyl)phenylsilanes (941. 61

13. Stereochemistry of Alkoxide-Induced Rearrangement- Displacements of (+)-(Bromomethyl)methyl(l-naphthyl)- phenylsilanes (8.). 76

14. Reaction of (+)-(Bromomethyl)methyl(l-naphthyl)phenylsilane (&) with Varied Amounts of Tetrabutylammonium Fluoride. 82 LIST OF FIGURES

Figure Page

1. Logarithms of the Migratory Aptitudes (Ar/Ph) Plotted Against Sigma Values for Rearrangement-displacements of 53. with Fluoride Ion 22

2. Plots of the Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) Versus Sigma-zero Substituent Values for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-f) with Fluoride Ion at 23 °C. 34

3. Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) Plotted against Sigma-zero Substituent Values for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-Q with Fluoride Ion at 0 °C. 37

4. Logarithms of the Migratory Aptitudes ip-Z -P h/P h) Plotted Against Sigma-zero Values for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-f) with Fluoride Ion at -20 °C . 38

5. Plot of the Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) against Sigma-zero Values for Reactions of Aryl(iodomethyl)diphenylsilanes (5a-f) with Fluoride Ion at 23 °C. 42

6. Plot of the Logarithms of the Ratios of Corrected Migratory Aptitudes for Substituted Phenyl Groups Versus Sigma-zero Substituent Values for Methoxide-induced Rearrangement-displacements of (4a-Q. 46

vii LIST OF FIGURES (cont.)

Figure Page

7. Structures of the Pentacoordinate Silyl Anionic Intermediates for Rearrangement-displacements of (4a-f1 with Methoxide and Fluoride Ions. 55

8. Transition States For Fluoride-induced Rearrangement- displacements of Aryl(halomethyl)diphenylsilanes which Express Aryl Participation Processes and Cationic Cleavages. 57

viii CHAPTER I : STATEMENT OF PROBLEM

The present research involves investigation of the electrical requirements and the stereochemistry of nucleophile-induced rearrangement-displacements of (halomethyl)triorganosilanes JL in which R = alkyl or aryl (Equation 1). The reactions of interest involve attack of a nucleophile at silicon rather than carbon to give a presumed pentacoordinate silyl anion 2. Collapse of the silicanionic species (2J via migration of an organic substituent from silicon to carbon with expulsion of bromide to give products of skeletal rearrangement, 2., has been documented by previous investigators.1*2

-X ^i— CH2R (1)

1, X = halogen 3. R = alkyl or aryl

1 2

There has been considerable concern as to the controlling features of such rearrangement-displacement reactions and therefore the purpose of this research is to investigate further the mechanistic details of these processes. The first part of this work involves determination of the migratory aptitudes of the rearrangement-displacements of a series of aryl(halomethyl)- diphenylsilane,s 4 and 5., with fluoride and alkoxide nucleophiles (Equation 2). Study was made of the effects of temperature, the halide leaving group, the nucleophile and general reaction conditions on the migratory aptitudes in the rearrangement-displacements.

Nu Ph— Si— CHgX- I Ph 4 ,5

X = Br Nu— Si— CH2Ph 4a, z = c f3 5a, z — c f3 I 4£, Z = Cl 5b, Z = Cl Ph 4a, z = H 5s, Z = H Ih 44. Z = CH3 5 4 , z = c h 3 4fi, z = o ch 3 5s, z = och3 41. Z - N(CH3)2 5f, Z = N(CH3)2 3

The results from the present migratory aptitude studies along with earlier investigations *>2 lead to interest in the stereochemistry at silicon in the rearrangement-displacement reaction. The second part of this work therefore involves determination of the stereo chemistry of the rearranged product 9 derived from reactions of the chiral silane, (bromomethyl)methyl(l-naphthyl)phenylsilane (8_1 with alkoxide and fluoride nucleophiles (Equation 3). Correlations of configuration using reactions of known stereochemistry for 8. and £

Nu 1 - Np— jji— CH2Br ► 1 -Np—-c; j— CH2Ph (3)

Ph CH3 [a]23D +8.29

a were used to determine whether the rearrangement-displacements occur with inversion, retention or racemization at silicon. CHAPTER II: HISTORICAL

Although the first organosilane, tetraethylsilane was prepared by Friedel and Crafts in 1863, 3 organosilanes did not generate much interest until the past three decades. 4 Of historical interest to the research in this dissertation is that halomethyltriorganosilanes (2., R = alkyl or aryl) react with nucleophiles to give various products two of which, 10. and 1_L, are indicated in Equation 4.

R R R

R— j>i— CH2X NxUC" ► R— Si— CH2Nuc + Nuc— Si— CH2R (4)

R R R 2. IQ 11

Early work by Whitmore and Sommer5 illustrated that

(chloromethyl)trimethylsilane (12) is more reactive to Sn 2 nucleophilic displacement (Equation 5) than its carbon analog, neopentyl chloride. The increased reactivity of J_2_ is due to less steric hindrance (13) because of the greater length of its carbon- silicon bond (1.90 A). 6

4 5

Si(CH3)3 Nuc' -C l' (CH3)3SiCH2CI- NuC""C > — Cl (CH3)3SiCH2Nuc (5)

H H 12 12 1A

As summarized in Table 1 and Equation 5 carbon-displacement reactions of chloromethyltrimethylsilane are useful for preparing various a/p/ta-substituted tetramethylsilanes.

Table 1. Displacement Reactions of (Chloromethyl)trimethylsilane (1_2) with Various Nucleophiles.

Nuc' (CH3)3SiCH2CI (CH3)3SiCH2Nuc -C l'

Wu.cl.eop.hile Solvent Eio.d uc.t/Y ieid Referer

Nal CH3COCH3 (CH3)3SiCH2l / 70% 7

NaOCH3 c h 3c h (CH3)3SiCH2OCH3 / 75% 8

k o 2c c h 3 c h 3c o 2h (CH3)3SiCH20 2CCH3 / 92% 9

KSCN c h 3c o c h 3 (CH3)3SiCH2SCN / 90% 1 0

C eH ^N ^ neat (CH3)3SiCH2NHC6H1! / 90% 1 1

NaN3 [(CH3)2n ] 3PO (CH3)3SiCH2N3 / 95% 1 2

(CH3)3P neat (CH3)3SiCH2P(CH3)3+CI' / 50% 13 6

An important historical reaction for the present work is the finding by Speier14 that (chloromethyl)trimethylsilane (121 reacts with alkoxide ions in alcohols (Equation 6) to give (alkoxymethyl)- trimethylsilanes (15’) and alkoxytrimethylsilanes (161 ?H, ch3 ch3 CH-§i~CH2C I-^ - •CH— f CH2OR + CH— § i— CH3 (6)

ch3 CH3 CR

1 2 15 1 5 R = CH3 75% 0% ch2ch3 70% 11% ch2ch2ch2ch3 19% 31%

The unusual products 16 are presumed to result from alkoxide attack on silicon to form pentacoordinate silyl anions 17. followed by silicon-carbon bond cleavages to give 1JL along with chloromethide ion which protonates to chloromethane (Equation 7).

CH, NaOR. -CH2CI' 1 2 RC— sF^3h2- ■Cl RCH : (CH3)3SiOR + CH3CI (7) (H+) ch3 ch3 17 15

Halomethylsilanes (£) were subsequently found to undergo unusual skeletal rearrangements with electrophilic or nucleophilic reagents. Electrophilic reaction of chloromethyltrimethylsilane (121 with aluminum chloride15 gives the intramolecular skeletal 7 rearrangement-displacement product, chloro(ethyl)dimethylsilane (18. Equation 8).

( 8)

(12 .) (12 )

Aryl(chloromethyl)dimethylsilanes 19a-c and aluminum chloride yield (arylmethyl)(chloro)dimethylsilanes (221 and aryl(chloro)ethylmethylsilanes (211 (Equation 9). 16 The relative ease of migration of the varied substituents is: p-M eC6H4 > C 6 H 5 > p-

CIC 6 H 4 » CH3 . The results indicate that cationic demands and pi- participation in 20. control the rearrangement processes. 8

Skeletal rearrangement-displacement reactions can also be induced by nucleophiles. 17 Aryl(chloromethyl)dimethylsilanes (19) react with sodium ethoxide in ethanol to give (1) aryl(ethoxymethyl)dimethylsilanes (231. the products of nucleophilic substitution at carbon (Equation 10), (2) aryl(ethoxy)dimethylsilanes (24) by nucleophilic displacements of chloromethide anion from silicon (Equation 11) and (3) (arylmethyl)(ethoxy)dimethylsilanes (25). products of nucleophilic attack at silicon with migration of the aryl groups from silicon to carbon (Equation 12).

Ar -Cl CHg— S i— CH2OCH2CH3 ( 10)

CH3 2 3

Ar Ar 1 . ^ NaOEt -'CH2CI I CH— S i CH2CI EtQ|q C H ~ S i—OCH2CH3 ( 11)

< H CH3 M IS och2ch3 -Cl CH— Si— CH2Ar ( 12) A r ------™ * 2 3 Z = Cl, H, CH3i OCH3

The cleavage and the rearrangement-displacement reactions in Equations 11 and 12 are presumed to involve nucleophilic attack of ethoxide at silicon of j_9 to form pentacoordinate intermediates 2_6 (Equation 13). The pentacoordinate silicon anions undergo migrations of their aryl groups from silicon to carbon to give (arylmethyl)ethoxydimethylsilane (25) and chloride ion, or silicon- carbon bond cleavage to yield chloromethide anion and ethoxydimethylarylsilane (24).

pH3

CH— § i— CHg—© —Z

-Cl OCH2C Hj 23

(13) EtO' 12 CH3 ~ S ^ 2 _ C I 6 h 3 o c h 2c h 3

23 CH3— |3 i OCHgCHg

ch3

The products of aryl migration (25) from reactions of 12. with ethoxide ion were not isolated because the ethoxysilanes undergo rapid nucleophilic attack by second equivalents of ethoxide ion to give diethoxydimethylsilane (26) and para-substituted toluenes. The toluenes are formed by silicon-benzylcarbon cleavage of 23. and protonation of the benzyl anions generated (Equation 14). 10 OCHoCHo OCH2CH3

CH3— S i— CHg— A r-p — S i—OCH2CH3 +p -ArCH3 (14)

ch3 ch3 23 23

The proportions of aryl rearrangement products (Table 2) via Equation 13 depend on the para substituent in the order: p-H< p-

CH 3CX p-CH 3< p-Cl. Substituent effects on overall rates of reaction are p-CH30< p-CH 3 < p-H< p-Cl. Rearrangement-displacement therefore is enhanced by the presence of an electron-withdrawing substituent in the para position of the aryl group. It is not clear as to the reason for the unusual position of unsubstituted phenyl group in the rearrangement order.

Table 2. Products (% Yield) of Reactions of Aryl(chloromethyl)- dimethylsilanes (191 with Sodium Ethoxide in Ethanol (Equations 10, 11 and 12).

_Z______Substitution(23) Rearrangements) Cleavaae(24) H 42 3 2 16 Cl 22 4 3 18 ch3 31.5 38.5 14 OCH3 30.5 35.5 16.5

A further example 18 of rearrangement-displacement under basic conditions is reaction of (chloromethyl)dimethylsilane (27) with potassium hydroxide in ethanol (Equation 15). The mechanism of the 11 reaction is believed to occur via nucleophilic attack of hydroxide at silicon to form the pentacoordinate intermediate 2j5_ which then collapses by hydrogen migration from silicon to carbon with expulsion of chloride ion to give hydroxytrimethylsilane (29 s). Hydride migrates better therefore than methyl.

H H j>Ha OH’ - CHo— S i— CH2C I-^ -> HD— J j i— CHg— C -CHg-^i— CH (15) | EtOH CH3 CH3 c h 3 CH3

21 23. 23

The ability of a nucleophile to attack carbon or silicon preferentially in (halomethyl)triorganosilanes is dependent on the nature of the nucleophile and the solvent. 19 Table 1 (see page 4) illustrates nucleophilic displacements which occur exclusively at carbon under the conditions used. Examples are now cited which show nucleophilic attack at silicon to give cleavage or rearrangement-displacement products. Equations 16, 17 and 18 illustrate reactions of (bromomethyl)trimethylsilane (30s) with sodium methoxide to give: (1) methoxytrimethylsilane (16s). (2) (methoxymethyl)trimethylsilane (15s). and (3) ethyl(methoxy)- (dimethyl)silane (3Is). The products and yields are summarized in Table 3 for reactions of 20. with sodium methoxide under varied conditions. 1 2 CH3 ’CH2Br I C H s-S i— OCH3 + CH3Br(16)

CHa 1 5 CHq ch3 NaOCH3 -Cl CH3—5 i— CHg— Br CHo— S i— CH— OCHa (17)

Ah3 CH., i n aa OCH 3

■Cl' CHg—Si— CHg- CH3 (18)

ch3 a i

Table 3. Product Distributions (% Yields) for Reactions of 30 with Sodium Methoxide in Varied Solvents.

SftlY ant 1 5 1 5 a i c h 3o h 98 0.5 0 50% CH3OH, Dioxane 96 1 .2 0.3 5% CH3OH, Dioxane 24 9 6 0 Dioxane 1 6 >80

In a hydrogen bonding solvent such as methanol, methoxide anion attacks 10. exclusively on carbon to give 15. the product of nucleophilic substitution ( Equation 19). Structure 32. in Equation 19 illustrates that the transition state for displacement on carbon is that of a typical Walden inversion. 20 1 3

(CH3)3Si H ch3o - 5. \ / 8- aa CH30 “ C------Bru‘— ► (CH3)3SiCH2OCH3 (19) -Br-

When the solvent is changed to dioxane, an aprotic solvent, methoxide anion attacks the silicon center in IQ. to give products of (1) silicon-bromomethide cleavage (16, Equation 20) and (2) methyl

CH3 CH30 ' L -CHoBr CH30 —-xS^ p H 2Br (CH3)3SiOCH3 (20)

CH3 ch3

aa 15 migration from silicon to carbon with expulsion of bromide ion (31. Equation 21). Species 3 3 in Equations 20 and 21 is the pentacoordinate silyl intermediate presumably formed by attack of methoxide at silicon in 30.

CH3 3 ch 3o; -B r’ I '? * ^ CH— | i — CH2CH3 (21) aa CH30 —\S ^ —CH2—B r

CH3 ch3 OCHs as a i 14

Spectacular solvent effects are also exhibited in reactions of (chloromethyl)dimethyl(vinyl)silane (341 with sodium methoxide in methanol (Equation 22). 21 The major product, di methyl (meth ox y- methyl)vinylsilane (351. results from methoxide displacement at carbon. Methoxy(dimethyl)vinylsilane (361 is formed by methoxide attack at silicon followed by silicon-carbon bond cleavage and loss of chloromethide anion.

CH=CH2 CH=CH2 CH=CH2 (22) I CH3O' I I (CH3)2SiCH2CI ►(CH3)2SiCH2OCH3 + (CH3)2SiOCH3 + (CH3)2Si(OCH3)2 CH3OH 24 25 15 22

76% 12% 12%

The third product, dimethoxydimethylsilane (37. Equation 22), is of particular interest in that it results from methoxide attack at silicon presumably as in Equation 23. Migration of the vinyl substituent from silicon to carbon with loss of chloride yields allylmethoxydimethylsilane (391. Reaction of 25. with methoxide ion then results in cleavage of the silicon-carbon bond of 4Q_ to give dimethoxydimethylsilane (371 and the allyl anion which protonates to propene (Equation 23). 1 5 CH3 c h 3

-Cl' M - H3° w (CH3)2SiCH2C H =C H 2

CH2=CH2 OCHa

as M (23) c h 3 c h 3 CH30 ' \V CH3O — S i^ p H 2CH = C H 2 "^►■(CH3)2Si(OCH3)2 + CH3CH = CH2

OCHj

4 £ az

Reactions of 2_4. with sodium methoxide in dioxane yield products (Equation 24) that differ significantly from those in methanol. The major product, allyl(methoxy)dimethylsilane (391. is not isolated in the reactions performed in methanol (Equation 22). Silane 39. is the product of nucleophilic attack at silicon, migration of the vinyl group to carbon and loss of chloride (Equation 23). Dimethoxydimethylsilane (37) is then formed by attack of methoxide on 39. with displacement of allyl anion (Equation 23).

c h 3o- F * (24) M 5 i ^ ? " (CH3)2SiCH2CH= CH2 + (CH3)2Si(OCH3)2+ (CH3)2|iOCH3

CHf=CH aa az as

45% 19% 9% 1 6

The final product, methoxy(dimethyl)vinylsilane (36) is presumed to result from methoxide attack at silicon with expulsion of chloromethide ion (Equation 25).

CH3 ch 3

Dioxane

aa a £

Conclusions drawn from the above examples and other investigations 24 are that a nucleophiles ability to attack silicon is dependent on its being small, "naked" and able to form strong bonds with silicon. For sodium methoxide in dioxane the sodium cation is well solvated, but the methoxide anion is not and therefore attack of the naked alkoxide occurs readily on silicon. Fluoride ion in acetonitrile has also been found to be effective for nucleophilic reactions on silicon. Fluoride is small, forms very strong bonds with silicon and is poorly solvated in polar aprotic solvents. In reaction of 34 with sodium methoxide in methanol, the methoxide ion is highly hydrogen bonded, its nucleophilicity for silicon is diminished and thus preference for attack on carbon occurs.

An experiment that provides insight into the electrical requirements for rearrangement-displacements on silicon is 17 treatment of (chloromethyl)dimethylphenylsilane (41_) with sodium

methoxide in dioxane (Equation 26). 19

(26) c h 2c h 3 9 N a O C H ^ (CH3)^ jOCH3+CH ' j0 c H 3+ (CH3)2SiCH2- Q (CH3)2SiCH2C I^— £ 30 UC r ll OCHj

41 4 2 4 2 4 4

3% 14% 79%

Formation of (methoxy)dimethylphenylsilane (42). a minor product, results from methoxide attack at silicon with expulsion of chloromethide ion, similar to earlier examples (Equations 7, 13 and 20). The interesting products of this experiment are ethyl(methoxy)(methyl)phenylsilane (43) and benzyl(methoxy)- dimethylsilane (441. Formation of rearrangement-displacement products 43_ and 44. is presumed to result from collapse of pentacoordinate intermediate 4jL in Equation 27 by either methyl or phenyl migration from silicon to carbon and loss of chloride. An important conclusion from the product yields, after statistical correction for the two methyl groups and one phenyl group in 41_, is that the phenyl group migrates eleven times faster than a methyl group. This was attributed to the ability of a phenyl group to better accommodate negative charge in the transition states for rearrangement-displacement. 1 8

(CH3)2SiCH2—O OCHa -Cl' 11 CH30' _9 K ^ ( ^ 11 CH30— Si— pH2— Cl (27) V > b b ch 3 ch 3 s - c 1 5 CH3^iCH2CH3

OCHa 12

Aryl(chloromethyl)dimethylsilanes 16, when similarly treated with sodium methoxide in dioxane at 60 °C, give rearrangement- displacement products of aryl f51 ) and methyl (52) migration

(Equation 28). 1 The migratory aptitudes for aryl/methyl migrations for the following aryl substituents are: P-CF 3 >m-Cl > p-Cl > P-CH 3 >

P-OCH 3 > H. Except for the unusual result where Z = H, the migratory aptitudes follow an order in which aryl groups with greater electron withdrawing capabilities migrate better. These results tend to suggest that the ability of a group to accommodate negative charge in the pentacoordinate intermediate 18. dictates the migratory ability. 19 (CH3)2^iCH2Ar

Nuc

Ar Ar a " C|- 4$, Nuc = F Nuc’ -I '- 'V r * SI, Nuc = OCH3 (CH3)2SiCH2CI Nuc— Si— pH,— Cl / V > b (28) b ch 3 ch 3 s Ar ■c 4£ CH3j>iCH2CH3 47. Nuc = F Ar = Z-C0H4 IS, Nuc = OCH3 Nuc 5S, Nuc - F 52, Nuc = OCH3

D am rauer 25 studied the rates of rearrangement-displacements of 46 using potassium fluoride solubilized by 18-crown-6 in aromatic solvents at 55° C (Equation 28). The reactions involve fluoride attack at silicon to form 47. followed by aryl migration to give 42. or methyl migration to yield 50, (Equation 28). The relative rates of reaction as monitored gas chromatographically by the disappearance of 46. were found to be in the order: aryl = m-(trifluoromethyl)phenyl, 5.7 > p- chlorophenyl, 2.9 > p -fluorophenyl, 1.7 > phenyl, 1.0 > p- methylphenyl, 0.63. The data suggest that the ability of an aryl group to stabilize negative charge in formation of 47. will increase the rate of attack on silicon. No firm conclusion with respect to the migratory aptitudes could be established from this work.

In this laboratory Aprahamian determined the electrical effects on the migratory aptitudes of para-substituted-phenyl and unsubstituted-phenyl substituents in reactions of aryl(chloromethyl)diphenylsilanes £2. with fluoride ion (Equation 29). 26

(C6HS)2S,CH2C f^ s^ chci

M -Cl'-Cl F—Si— CH2C6 H5

Z = CF3i Cl, H, CH3, OCH3i N(CH3)2 c 6 h 5

The statistically corrected migratory aptitudes for reactions of 5-2. with tetrabutylammonium fluoride at 0 °C in tetrahydrofuran are listed in Table 4. Substituent effects on migratory aptitudes are small. Para-electron-withdrawing groups cause the substituted phenyl groups to migrate faster than phenyl. * Electron-donating para -substituents however do not retard migration. Thus the para- methoxy and the para-methylphenyl groups rearrange at essentially 21 Table 4. Migratory Aptitudes (Ar/Ph) for Reactions of 55. with Fluoride Ion at 0 °C in Tetrahydrofuran (Equation 29). Z Z

(C6 H5)2SiCH2CI- •(C6 H5)2SiCH2—\ \ ^ Z + C6 H5SiCH2C6 H5

5 5 5 5 L 5 5

z Ar/Ph

c f 3 3.00 Cl 2.01 H 1.00 ch 3 0.98 o ch 3 0.97 N(CH3)2 1.13

the same rates as does phenyl. Interestingly, the p a r a - dimethylaminophenyl group migrates slightly faster than phenyl. A free energy plot of the logarithms of migratory aptitudes versus sigma values for the para-substituents gives a "curved" correlation (Figure 1). 22 0.5 i Q CF,

0.4

0.3- 0 Cl

log Ar/Ph

0.1 ■ N(CH3)2 □

0.0 - □ □ □ H OCH3 CH -0.1 -I ■■■■ I -■ ■ I ■ I T ■—r I I 1 ■ I ' ■ I -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 sigma

Figure 1. Logarithms of the Migratory Aptitudes (Ar/Ph) Plotted Against Sigma Values for Rearrangement-displacements of 53. with Fluoride Ion.

The facts that electron-donating substituents do not retard migration and Hammett plots such as Figure 1 are not linear raised significant questions as to the mechanisms of rearrangement- displacements of halomethylsilanes by fluoride ion. Among the mechanisms considered to explain these effects was pseudorotation of silicanionic intermediates during the rearrangement- displacements and changes of sigma and /?i-electronic contributions of the substituted-phenyl groups during rearrangements. It was these concerns that raised further interest as to the electronic and eventual stereochemical effects that lead to rearrangement- 23 displacements in halomethylsilanes. It was the purpose of the research in this dissertation to study the effects of varied temperatures, leaving groups, nucleophiles and reaction conditions on rearrangement reactions. A stereochemical study was initiated to investigate pseudorotation as a potential mechanism in these reactions. CHAPTER III: PREPARATION AND REACTIONS OF ARYL(HALOMETHYL)DIPHENYLSILANES

A ryl(brom om ethyl)diphenylsilanes (4g^s.) in which the aryl substituents are para-substituted (Z = CF 3 , Cl, H, CH3 and OCH 3 ) were synthesized by the sequence in Equation 31. The Gilman method27, reaction of dichlorodiphenylsilane (611 with one equivalent of the

Cl H ArLi or ArMgBr I LiAll-L I Ph2SiCI2 ------^ A r —Si— Ph--— ► Ar—Si—Ph Et20 T Et20 f Ph Ph £1 £2 £2 (31)

Ph Ph PhHgCBr3 I 1. n-BuLi I /TTJ—on ° r ^ Ar— Si- CHBr2 A r—Si—CH2Br C6 H6, 80 C | * Et20/-78 C | Ph 2 . HBr Ph

M la-a

Ar = z “ 0 ~ 4a, z = cf3 41a, z = ci 4s, z = H 4d, z = ch3 4a, z = och 3

24 25 appropriate para-substituted-aryl Grignard or lithium reagents (661 was used to prepare arylchlorodiphenylsilanes &2. Organometallics

6 6 were obtained from the appropriate para-bromo-substituted- benzene (651 and magnesium, lithium or n-butyllithium (Equation 32). The arylchlorodiphenylsilanes (621 were not isolated and,

/=K Li, Mg or n-BuLi Z~ 0 - Br ------^ ------► Z - Q - M (32)

M = Li or MgBr

after filtering the magnesium or lithium salts formed, were reduced by lithium aluminum hydride in ethyl ether to aryldiphenylsilanes

63..

Silanes 63. undergo dibromocarbene insertions into their silicon-hydrogen bonds upon reactions with phenylmercuriotribromomethane (681 in benzene at 80 °C to give aryl(dibromomethyl)diphenylsilanes (64. Equation 31). 28 Mercurio reagent $_§. was prepared from phenylmercuric bromide (671. tribromomethane, potassium r-butoxide and r-butanol in tetrahydrofuran at -20 °C

(Equation 33). 29 Treatment of 64. with one equivalent of n- butyllithium at -78 °C to effect metal-halogen exchange, followed by hydrogen bromide gas yielded aryl(bromomethyl)diphenylsilanes

4a-e (Equation 31). 30 PhHgBr + CHBr3 KO/-Bu/f phHgCBr3 (33) THF, -20^C

£ 2

The route in Equation 31 was not used to prepare

(bromomethyl)(/7 -dimethylaminophenyl)diphenylsilane (4f) due to complications in the reaction of (dimethylaminophenyl)- diphenylsilane (63f) with phenylmercuriotribromomethane (681. The product, 4f, of insertion of dibromocarbene into the silicon hydrogen bond of 63f was not obtained (Equation 34). Presumably the dibromocarbene generated from decomposition of phenylmercurictribromomethane ( 6 _8_) reacts faster with the lone pair electrons on nitrogen than with the silicon-hydrogen bond in 63f.

(CH3)2N \ H + PhHgCBr3 -X -> -(C H 3)2N—^ - 5 i —CHBr; Ph -PhHgBr Ph (g4)

Silane 4£. was prepared as outlined in Equation 35. Commercially available methyltrichlorosilane (691 was thus brominated with a mixture of bromine and chlorine to give (bromomethyl)trichlorosilane (701 31, treatment of which with 2 equivalents of phenylmagnesium bromide yielded 27 (bromomethyl)diphenylchlorosilane (71) that was isolated via tedious vacuum fractional distillation. Reaction of 2J_ with p- dimethylaminophenylmagnesium bromide in tetrahydrofuran gave 4f in suitable quantities for the desired studies.

Cl Cl I Brp/CI? I 2 PhM9Br Cl— jji— CH3 ------— ► Cl— j>i— CH2Br ------►

Cl Cl

M 10 (35)

Ph Ph I ^ p-(CH3)2NPhMgBr / = \ I. — ► CI— 1> i—CH2Br — — ► (CH3)2N -^-Si-C H 2Br

Ph Ph

11 4_£

Silane 7 0 was also prepared by reaction of chloromethyltrichlorosilane (72) with aluminum tribromide in ethyl bromide as in Equation 36. 32

Cl Cl I AIRro I Cl—^i— CH2CI ■ 3-----► Cl— CH2Br (36)

Cl Cl 12 m

Aryl(iodomethyl)diphenylsilanes 5a-f were obtained by displacements of aryl(halomethyl)diphenylsilanes 2 1 (the halogen 28

was chlorine33 or bromine) with sodium iodide in acetonitrile at 80 OC (Equation 37). 7

Ph Ph I CH CN • Ar— Si—Cf-feX + Nal — ------► Ar—Si-CH2I (37) | -NaX | Ph Ph

Za X = Cl, Br Saifi Ar= z -^ O - £d,5fi>z z = = Hch3 5a, Z = CF3 gg, z = och 3 512, z = Cl 5f, Z = N(CH3)2

Silanes 4 and £ (Z = CF 3 , Cl, CH3 , OCH3 and N(CH3)2) are previously unreported. The silanes gave good carbon and hydrogen combustion analyses and their spectral properties (infrared, mass and NMR) are in accord with the assigned structures.

REACTIONS OF ARYL(HALOMETHYL)DIPHENYLSILANES WITH FLUORIDE ION

Fluoride-induced rearrangement-displacements of (halomethyl)silanes are known processes. 34 In the present reactions tetrabutylammonium fluoride (TBAF) was used as the fluoride source because of its solubility in tetrahydrofuran and it afforded unsolvated fluoride ion of excellent nucleophilicity towards silicon. 29

Aryl(bromomethyl)diphenylsilanes f4a-Q were reacted with 2.3 equivalents of commercial 1 M tetrabutylammonium fluoride in tetrahydrofuran at 23 °C. The fluoride reagent was added over two minutes to a silane in tetrahydrofuran and the reaction mixture was stirred 18 hours. Thin layer chromatography indicated that the starting silane was depleted in less than three minutes.

Fluoride ion reacts with silanes 4a-f by attack on silicon (Equation 38). Migration of an aryl or a phenyl group from silicon to carbon with expulsion of bromide yields an (arylmethyl)fluoro- diphenylsilane (7 al or an aryl(benzyl)(fluoro)phenylsilane (Zk)- Attack of fluoride ion on silicon is presumed to form pentacoordinate intermediates 74. (Equation 38). There is no direct evidence as yet however to support formation of JA. as a distinct intermediate.

TBAF Ph— Si—CH2Br

4.3-1

Ph Jh 30

In principle the mole ratios of JSL and 50% 2k (Ar/0.5Ph) yield the migratory aptitudes for rearrangement-displacement reactions of 4a-f with fluoride ion. Because of the susceptibility of 2a. and 2 k to

attack by fluoride ion, direct measurements of the yields of 2 a. and 7 b were not reliable. It was found satisfactory, however, to

determine the yields of toluenes 2 k and 28. that result from reactions of 2a. and 2b with a second equivalent of fluoride ion as in Equation 39. Fluoride attack on 2a. and 2k induces cleavage of the varied benzyl-silicon bonds to give the corresponding benzyl anions which are protonated by the water in the TBAF reagent to yield 2k and 7 8 .

TBAF

Zk 27 23.

Toluene (2fD and para-substituted-toluenes (76) resulting from reactions of 4a-f with excess fluoride ion (Equation 41) were readily analyzed via capillary gas chromatography. The yields of 28. and 7_6 were determined using internal standard methodology upon adding 3 1 known amounts of anisole at the beginning of a reaction or after initial work-up. Peak areas for ZiL and 2JL were corrected for response factors of the flame ionization detector from calibration

curves of authentic samples of toluene (7 8 ) or the substituted- toluene (76) and the internal standard anisole. Authentic samples of toluene (2R) and substituted-toluene products (76) were purchased

except for 4-trifluoromethyltoluene (76a. Z = CF 3 ) which was prepared from para-trifluoromethylphenylmagnesium bromide (79)

and methyl iodide (Equation 40). 35

CF 3 - 0 “MgBr + CH3 I > CF 3 -O-CH 3 (40) -MgBrl

7 9 ZSa Z = CF3

The migratory aptitudes for rearrangement-displacement reactions of 4a-e with fluoride ion were calculated by dividing the percent yields of substituted-toluene (76) by the percent yields of toluene (78) and statistically correcting for the two phenyl and one aryl substituent in the initial silanes (4a-f). The combined yields, moles of toluene (78) plus moles of para-substituted-toluene (76). of the products are quantitative. Each experiment was performed at least three times and the data are reproducible. p-Z-Ph Y'° f a

Ph— — CH2Br2.3 equiv TBAF i f D + L [) (41) THF ^ ^ Ph (H20)

i S L J 1 3 1 3

The statistically corrected migratory aptitudes for fluoride- induced rearrangement-displacements of 4a-f at 23 °C as in Equation 41 are summarized in Table 5.

Table 5. Statistically Corrected Relative Migratory Aptitudes and Sigma-zero Values for Reactions of para-Aryl(bromomethyl)diphenylsilanes (4a-f) with Tetrabutylammonium Fluoride at 23 °C (Equation 41).

Ar/Ph______siama 0

c f 3 2.43 ± 0.24 0.53 Cl 1.79 ± 0.18 0.24 H 1 .0 0 ± 0 .1 0 0 .0 0 t

c h 3 0.967 ± 0.097 o o c h 3 1 .0 0 ± .1 0 -0 . 1 2 N(CH3)2 1.30 ± 0.13 -0.32

The data in Table 5 reveal that substituent effects on the relative migratory aptitudes of phenyl versus para-substituted- phenyl groups in fluoride-induced rearrangement-displacements of 4 are small. Phenyl groups with electron-withdrawing substituents (Z 33 = CF3 and Cl) in the para position migrate faster than phenyl. When

the para-substituents are electron-donating (Z = CH 3 and OCH 3 ) the

migratory abilities of the substituted phenyl groups are essentially

the same as for phenyl groups. For 4f, Z = N(CH 3 )2 , the migratory aptitude of the p-dimethylaminophenyl group is significantly larger than for the phenyl group.

Hammett free energy plots frequently correlate the electrical effects that substituents have on a reaction system. The plot of the logarithms of the migratory aptitudes in Table 5 versus sigma-zero values for para phenyl substituents is illustrated in Figure 2. Sigma-

zero substituent constants 36 are used for systems in which there is no conjugation between the substituent and the reaction site. Thus sigma-zero values correlate the rate constants of hydrolysis of aryldiphenylsilanes (80J in wet piperidine (Equation 42). 3 7

Although sigma-silicon substituent constants 38 have been developed to account for the interactions of the p-d pi orbitals between aryl groups and silicon, they have no advantage over sigma-zero values.

Ar H20 Ph— Si— H (piperidine) Ph Ph

f il

Ar = C6 H4-Z

Z = p-CI, H, /77-CH3, p-CH3, /77 -N(CH3)2, p-OCH3, p-N(CH3)2 34 0 . 4 - i □ CF3

0 . 3 -

□ ci

0.2 -

l o g ^ □ N(CH3)2 0.1 H

0.0 - OCH30 b h b ch 3

- 0.1 1— r 1 — *— »— T -0.4 -0.2 0.0 Q 0.2 0.4 0.6 s ig m a

Figure 2. Plots of the Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) Versus Sigma-zero Substituent Values for Reactions of Aryl(bromomethyl)diphenylsilanes f4a-f) with Fluoride Ion at 23 °C (Equation 41). 35

The Hammett plot in Figure 2 does not give a satisfactory linear

correlation and consequently is of concern. Since earlier work 40 indicates that reaction temperatures affect correlations of rearrangement-displacements of (halomethyl)silanes, the behavior of 4 with fluoride ion was studied at 0 °C and then at -20 °C.

Reactions of 4. with fluoride ion at 0 °C and at -20 °C were performed by adding 2.3 equivalents of tetrabutylammonium fluoride in tetrahydrofuran in two minutes to 4_ stirred in tetrahydrofuran at the desired temperature. The solutions were stirred for 30 minutes and placed in a refrigerator (0 °C, 10 days) or a freezer (-20 °C, 21 days). After depletion of the starting material 4j. as indicated by thin layer chromatography, the reaction solutions were stirred at room temperature for 18 hours to assure quantitative cleavage of the arylmethyl groups in 7a and in (Equation 39). 41 Experiments worked up shortly after depletion of the starting material 4., without allowing for cleavage, gave poor yields of 2Jl when the para substituents are dimethylamino, methyl and methoxy.

Cleavage of the benzylic substituents in Za when Z = CH 3 , OCH3 and

N(CH 3 )2 , (Equation 39) is slow at 0 °C and -20 °C, and therefore stirring at room temperature was needed. Table 6 summarizes the migratory aptitudes for reactions of 4 with fluoride ion at 0 °C and -20 °C. The reactions of 4_ with fluoride ion were repeated a minimum of three times and the results are reproducible and give quantitative yields. 36 Table 6 . Statistically Corrected Relative Migratory Aptitudes (p-Z-Ph/Ph) in Reactions of Aryl(bromomethyl)diphenylsilanes (4a-el with Fluoride Ion at 0 °C and -20 °C (Equation 41).

Z Mean p -Z-Ph/Ph 0 0 0 -20 °C c f 3 2.77 ± 0.28 2.96 ± 0.30 Cl 1.92 ± 0.19 1.96 ± 0 .2 0 H 1 .0 0 ± 0 .1 0 1 .0 0 ± 0 .1 0 ch 3 0.96 ± 0 .1 0 0.93 ± 0.090 OCHj 1.05 ± 0.11 0.97 ± 0 .1 0 N(CH3)2 1.34 ± 0.13 1.36 ± 0.14

The data in Table 6 clearly indicate that the relative migratory aptitudes in reactions of 4 with fluoride ion at 0 °C and at -20 °C are similar to those at 23 °C (Table 5). As the temperature is lowered there is a small increase in the migratory abilities of phenyl groups containing para-electron-withdrawing groups (Z = CF 3 and Cl). For electron-donating p-substituents (Z = CH 3 , OCH3 , and N(CH 3 )2 ) however the migratory aptitudes are essentially the same as temperature is lowered. Figures 3 and 4 are Hammett plots of the logarithms of the migratory aptitudes (p-Z-Ph/Ph) versus sigma-zero values for fluoride-induced rearrangement-displacements of 4a-e at 0 °C and -20 °C, respectively. Figures 3 and 4 indicate that the trends in Hammett plots for reactions at 0 °C and -20 °C are similar to that in Figure 2 for reactions at 23 °C. 37 0 .5 -

■ □ CFg

0 .4 -

■

0 .3 - El Cl

■

0 .2 - logfl^ E H

□ N(CH3)2 0 .1 -

■ □ OCH3 o .o - □ H 0CH3

■

-0.1 - -0.4 -0.2 0.0 0.2 0.4 0.6

sigma 0

Figure 3. Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) Plotted against Sigma-zero Values for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-1) with Fluoride Ion at 0 °C (Equation 41). 38 0.5 h □ cf3

0 .4 -

0 .3 - □Cl

□ N(CH3)2

0.1 -

och 3 □ h 0 .0 - oP ch3

- 0.1 - 0 .4 -0 .2 0.0 0.2 0 .4 0.6 sigma 0

Figure 4. Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) Plotted Against Sigma-zero Values for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-f) with Fluoride Ion at -20 °C (Equation 41). 39

Of interest then was the possibility that a change in the leaving group could have significant effects on the migratory aptitudes in rearrangement-displacement reactions of aryl(halomethyl)diphenylsilanes. Fluoride-induced rearrangement-displace ment reactions were then conducted with aryl(iodomethyl)- diphenylsilanes (5a-e) and fluoride ion at 23 °C using procedures identical to those for rearrangement-displacements of aryl(bromomethyl)diphenylsilanes (4a-e). Equation 43 illustrates fluoride attack of 5a-e at silicon to give pentacoordinate species &2. which undergo migration of their p-substituted phenyl or phenyl groups to carbon with expulsion of iodide to give l a and Ih..

TBAF

In overall processes similar to Equation 41, 5a-f react with 2 equivalents of fluoride ion to yield toluene ('78') and substituted toluenes (761 (Equation 44) quantitatively via cleavage of 7a and 7J> (Equation 39). 40 QH3 2 equiv TBAF Ph— {•>’—CH2I + 0 (44) THF Ph (H20) z 7 3 1 3

The migratory aptitudes for reactions of 5a-e with excess fluoride ion are presented in Table 7. The migratory aptitudes in

Table 7 show trends identical to those in Tables 5 and 6 .

Table 7. Statistically Corrected Relative Migratory Aptitudes (p-Z-Ph/Ph) in Reactions of Aryl(iodomethyl)diphenylsilanes (5a-f) with Fluoride Ion at 23 °C (Equation 44).

Ph TBAF

(H20) Ph 1 3 1 3

Z (p -Z-Ph/Ph)

CF3 2.46 ± 0.25 Cl 1.65 ± 0.17 H 1.00 ± 0.10 CH3 0.96 ± 0.10 OCHg 1.07 ± 0.11 N(CH3)2 1.43 ± 0.14 4 1

Figure 5 is a plot of the logarithms of the corrected migratory aptitudes in Table 7 versus the appropriate sigma-zero substituent constants. As with Figures 2-4, figure 5 is a (non-linear) curved Hammett plot. It is concluded from the present reactions of aryl(halomethyl)diphenylsilanes (4 and 5.) with fluoride ion, along with previous w o r k 4 0 > that the nature of the halogen leaving group has little effect on the order or the sizes of the migratory aptitudes in rearrangement-displacement.

It was then of interest to investigate rearrangement- displacements of halomethylsilanes with different nucleophiles. Previous investigations indicate that alkoxide bases in dioxane effect efficient methoxide attack on silicon in (halomethyl)silanes to give rearrangement-displacement products. 1.22,23 Study was then initiated of reactions of aryl(bromomethyl)diphenylsilanes (4a-f ) with sodium methoxide in dioxane at 23 °C (Equation 45). Since sodium methoxide's solubility in dioxane is limited, the reaction mixtures were well stirred and large excesses of sodium methoxide (10-12 equivalents) were used. Methoxide ion is presumed to attack silicon in 4a-f to form pentacoordinate silyl anions 8J1 which collapse by migration of an aryl substituent and displacement of bromide to give 84. and 8j5_ respectively. The reactions were followed by thin layer chromatography and take approximately 36 hours to be completed. 42 0.4 -i

0 .3 -

q CI

OCHg

0.0 - □ H □CH.

- 0.1 - 0 . 4 - 0 .2 0.0 0.2 0 .4 0.6 sigma 0

Figure 5. Plot of the Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) against Sigma-zero Values for Reactions of Aryl(iodomethyl)diphenylsilanes (5a-ft with Fluoride Ion at 23 °C (Equation44). 43 Ph

CH3O— {j> i— CH2- Q —Z

- B y ^ Ph

Z M

(45) NaOCH3 i o a Ph— Sf-CH2Br r^- CH3O— Sh-^H 2Br [ 2 -N a Ph Ph Ph Z 4 a - f

-.A

CH3O— ^ i— CH2Ph

Gas chromatographic analyses of reaction mixtures from 4f and sodium methoxide reveal that, after depletion of all of the initial bromide, benzylic cleavage of M (Z = N(CH 3 )2 ) by sodium methoxide is slow. Fluoride ion is a more efficient nucleophile for cleaving silanes 84. and 85. than is methoxide. To facilitate and assure total cleavage of the benzyl group in and the substituted phenyl groups in 84., 2.3 equivalents of tetrabutylammonium fluoride were added after thin layer chromatography revealed depletion of 4a-f in reactions (Equation 46) with sodium methoxide. The reaction mixtures were stirred overnight with excess fluoride ion and worked up in the same manner as in earlier experiments. The experiments were repeated at least twice and the results are reproducible. The 44 statistically corrected migratory aptitudes for reactions of 4. with methoxide ion are summarized in Table 8 .

Ph Ph

c^ o- s £ ch2- Q - z ► CH30_si-F +

Ph 2 Ph CHa

M M 13.

(46)

nr CHo I (* TBAF w I I v CH30 Sj>i CH2Ph (h,20) CH30 Si F + A

Ph Ph 03. 01 10.

Although the effects are small, the migratory aptitudes in Table

8 indicate that para electron-withdrawing substituents (Z = CF 3 and

Cl) accelerate rearrangement of phenyl groups. The migratory abilities for these phenyl groups are similar to those in corresponding fluoride-induced rearrangement-displacements

(Tables 5 and 6 ). For phenyl groups with the para electron-donar substituents, Z = CH 3 and OCH 3 , in methoxide-induced rearrangement-displacements of 4_, the migratory aptitudes are slightly smaller than those with fluoride ion. When, however, the para phenyl substituent is dimethylamino the migratory ability of the para -dimethylaminophenyl group in reaction of 4f with 45 methoxide decreases to approximately one-half that with fluoride

(Tables 5 and 6 ).

Table 8. Statistically Corrected Relative Migratory Aptitudes (p-Z-Ph/Ph) for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-f1 with Methoxide Ion at 23 °C.

NaOCH3 — CH3 + PhCH3 2

1 3 13

Z Statistically Corrected Ar/Ph CF3 2.53 Cl 1.64 H 1.00

CH.'3 0.79 och3 0.84 N(CH3)2 0.68

Figure 6 indicates that the free energy correlation is more linear for rearrangement-displacements of 4. with methoxide than with fluoride (Figures 2-5). The slope (rho) of the line in Figure 6 is +0.72 with a correlation coefficient of 0.97 which indicates that the transition states for the migration processes are more negative than the parent silanes. From these data it can be assumed that aryl groups which best accommodate negative charge in the transition states of the rearrangement-displacement will migrate faster. It is emphasized that the electrical effect in the rearrangement processes is quite small. 46 0.5-1

CF; 0 . 4 -

0 . 3 -

0 . 2 -

o.o- □ H

An OCH; N(CH3) 2 / 0 CH3

- 0.2 0 . 4 0.2 0.0 0.2 0 . 4 0.6 sigma 0

Figure 6. Plot of the Logarithms of the Ratios of Corrected Migratory Aptitudes for Substituted Phenyl Groups (Table 8) Versus Sigma-zero Substituent Values for Methoxide-induced Rearrangement-displacements of 4a-f. 47

As has been summarized previously, Hammett plots (Figures 2- 5) of fluoride-induced rearrangement-displacements of 4a-f are curved whereas the methoxide-induced processes give a nearly

satisfactory linear free energy correlation (Figure 6 ). It was therefore an objective to investigate the curved Hammett plots. Because (bromomethyl)(4-dimethylaminophenyl)diphenylsilane (4f) gives the most significant deviation, its rearrangement-displacement reactions with nucleophiles were studied further.

Previous rearrangement-displacements of 4b were carried out with fluoride in tetrahydrofuran and with methoxide in dioxane. It was therefore of interest to vary the solvents in these two reaction systems. Table 9 summarizes the migratory aptitudes obtained for 4f upon changing solvents. The migratory aptitude of the p- dimethylaminophenyl group in fluoride-induced rearrangement- displacement in dioxane (1.24) is quite similar to that obtained earlier in tetrahydrofuran (1.30, Equation 41). Further, the migratory aptitude of the p-dimethylaminophenyl group in methoxide-induced rearrangement-displacement in tetrahydrofuran (0.69) is essentially identical to that in dioxane (0.68, Equation 45). These experiments rule out the possibility that the difference in migratory aptitudes of the p-dimethylaminophenyl group is due either to tetrahydrofuran or dioxane. Finally, when reaction of 4T with fluoride ion is performed in 96% hexane-4% tetrahydrofuran the migratory aptitude of p-dimethylaminophenyl is increased to 1.66 (p-(CH 3 )2 N-Ph/Ph). 48

Table 9. The Effects of Solvents on the Migratory Aptitudes for Rearrangement-Displacements of with Fluoride and with Methoxide Ion at 23 °C.

N(CH3)2

CH, CHo

Ph- fji— CH2Br + Nuc ------

Ph 4J 1 3 N(CH3)2 Z£Z = N(CH3)2

Solvent Nuc(source) Corrected p -(CH3)2NPh/Ph

Tetrahydrofuran F’(TBAF) 1.30 Dioxane F'(TBAF) 1.24 Tetrahydrofuran CH30'(Na0CH3) 0.69 Dioxane CH30'(Na0CH3) 0.68 96%Hexane/4%THF F’(TBAF) 1.66

Study was then made of the effects of fluoride concentration on the migratory aptitudes for rearrangement-displacements of M. and 4 b . In these experiments the conditions were varied by adding the bromomethylsilanes all at once to tetrabutylammonium fluoride (3 equivalence) in varying amounts of tetrahydrofuran. The corrected migratory aptitudes obtained in these experiments are listed in Table 10. For 4f, increasing the fluoride ion concentration from 0.004 molar to 2.44 molar results in an increase in the migratory aptitude of the p-dimethylaminophenyl group from 1.23 to 1.55. Increasing the fluoride ion concentration in rearrangement-displacement of 4J) 49 from 0.095 molar to 2.44 molar causes little change however in the migratory ability of the p-chlorophenyl group in rearrangement- displacement of 4b.

Table 10. Corrected Migratory Aptitudes for Rearrangement- Displacements of 41 and 4k. at Varied Concentrations of Fluoride Ion. Z

3eq TBAF

Z M TBAF Corrected p -Z-Ph/Ph

N(CH3)2 0.0040 1.23 N(CH3)2 0.043 1.26 N(CH3)2 0.087 1.37 N(CH3)2 0.14 1.33 N(CH3)2 0.26 1.33 N(CH3)2 2.44 1.51 Cl 0.095 1.80 Cl 0.19 1.86 Cl 2.44 1.82

That the migratory aptitude of the p-dimethylaminophenyl group in rearrangement-displacement of 41 by fluoride ranges from 1.23 to 1.53 raises the possibility that the tetrabutylammonium fluoride reagent contains acid which converts 4f extensively to its ammonium salt 88.- Thus in rearrangement-displacement of 8jL by fluoride, the p-dimethylaminophenyl group is more electron- 50 deficient and therefore migrates more readily than does phenyl from

8 9 (Equation 47). In order to evaluate the question that rearrangement-displacement of 4f by fluoride actually

t v v CHT‘i^L'ch3i N~" CH3-^L_ch3

Ph— Si— C H 2Br --- ► Ph— Sh - C H 2Br

Ph F7 Ph (47) M ^

Ph -Br; Ph— S i— ^H(CH3)2

F an involves £JL reaction of 4f. with tetrabutylammonium fluoride (3 equivalents) was conducted in the presence of tributylamine (3.5 equivalents). The corrected migratory aptitude found for the p- dimethylaminophenyl group is 1.37 (Table 11) and therefore similar to that in rearrangement-displacement reactions of 4f in the absence of the scavenger base (Table 10). Since tributylamine is expected to deprotonate 8JL> it is presumed that rearrangement-displacement of 4f does not occur as in Equation 47.

In perhaps a better experiment, the migratory aptitude of the p-dimethylaminophenyl group in reactions of 4f in dioxane at 23 °C 51 with a mixture of tetrabutylammonium fluoride (3 equivalents) and sodium methoxide (16 equivalents) is found to be 1.19 (Table 11), which is similar to the value of 1.24 obtained in fluoride rearrangement:displacement of 4f. in dioxane. Since tetrabutylammonium fluoride effects complete depletion of 4f in less than three minutes whereas approximately 36 hours is necessary for sodium methoxide, 4f in the presence of fluoride and methoxide reacts essentially totally with fluoride ion. The sodium methoxide present insures that 4£ is not converted to &§. which then undergoes rearrangement-displacement as in Equation 47.

In a further investigative experiment, reaction of 4f was effected in tetrahydrofuran with excess cesium fluoride instead of with tetrabutylammonium fluoride. Cesium fluoride is quite insoluble in tetrahydrofuran. Reaction of 4f occurs effectively however with cesium fluoride (9.5 equivalents) and results in a migratory aptitude of the p-dimethylaminophenyl group of 1.63 (Table 11). 52 Table 11. Corrected Migratory Aptitudes for Fluoride-Induced Rearrangement-Displacements of M. under Varied Conditions.

N(CH3)2

Nuc' Ph— < -CH2Br ^ * 23 °C CH, ch3 Z £ Z = N(CH3)2 13.

Special Corrected Nuc Solvent Condition p (CH3)2NPh/Ph

F’(TBAF) tetrahydrofuran 3.5 eq. Bu3N 1.37 F’(TBAF) dioxane 16 eq. Na O C H 3 1.19 F’(CsF) tetrahydrofuran 9.5 eq. 1.63 CHAPTER IV: DISCUSSION OF MIGRATORY APTITUDES

The most important conclusion obtained from migratory aptitude data for fluoride-induced rearrangement-displacement reactions (Tables 5, 6 and 7) and methoxide-induced rearrangement- displacement reactions (Table 8) of aryl(halomethyl)diphenylsilanes 4a-f and 5a-f is that substituent effects are small. The spread of the relative migratory aptitudes with methoxide as the nucleophile is 3.71 and the spread of relative migratory aptitudes with fluoride as the nucleophile ranges between 2.52 - 3.18. These results clearly indicate that the electrical requirements are small in these rearrangement-displacement reactions.

Methoxide and fluoride-induced rearrangement-displacement reactions of 4a-f give similar migratory aptitudes when the para- substituents are trifluoromethyl and chloro. It is clear in these cases that aryl groups (4a.b and 5a.bIwith electron withdrawing- substituents in the para position, migrate faster than unsubstituted phenyl substituents. The trends however are different when the para-phenyl substituents are electron-donating (CH 3 , OCH3 and

N(CH 3 )2 ). The relative migratory aptitudes with the electron donors are smaller for methoxide than with fluoride as the nucleophile. The 53 54 most significant difference is found when the migratory group is para-dimethylaminophenyl. In all experiments of fluoride-induced rearrangement-displacements of 4f, the p-dimethylaminophenyl group migrates faster than the unsubstituted phenyl group. In methoxide-induced rearrangement-displacements of 4f. p- dimethylaminophenyl however migrates slower than does phenyl.

At present the different behaviors of 4 with fluoride and with methoxide nucleophiles will be explained on the basis of differences in electrical effects in pentacoordinate silyl anionic intermediates 7.1 and 7.2 (Figure 7) presumably generated during rearrangement- displacement. It is thus proposed that silyl anions 7.1 are stabilized relative to 1*2 because of the great strength of silicon-fluorine bonds and the greater inductive effect of fluorine than oxygen. On the other hand, silyl anions 7.2 are destabilized relative to 7.1 because the methoxy group is less electronegative, bulkier and possibly a pi- electron donar during the rearrangement-displacement act. Since 7.2 is destabilized relative to 7.1. the transition state for collapse of 7.2 will be closer to its pentacoordinate precursor than that from 7.1. 5 5 Z z

F— Si— CH?Br / \ Ph Ph 7.1

Figure 7. Structures of the Pentacoordinate Silyl Anionic Intermediates for Rearrangement-Displacements of 4a-f with Methoxide and Fluoride Ion.

The migratory aptitudes for rearrangement-displacements of 4a-f by methoxide are readily explained. An acceptibly linear free energy correlation is obtained when logarithms of migratory aptitudes are plotted against sigma-zero substituent values (Figure

6 ). The small positive rho of 0.72 for the migratory aptitudes indicates that the transition states for rearrangement-displacement are negative compared to 4a-f. The ability to accommodate negative charge in the rearrangement transition states thus dictates the rates substituents will migrate. Aryl groups with electron-withdrawing substituents (CF 3 and Cl) thus migrate faster than those with electron-donating substituents (CH 3 , OCH3 and N(CH 3)2 ). Electron- withdrawing substituents can better relieve negative charge from pentacoordinate silicanion centers and therefore the transfer of the sigma bond from silicon to carbon will occur more readily.

Consequently electron-donating substituents (CH 3 , OCH3 and 56 N (C H 3 )2 ) lower the migratory abilities of aryl groups as the data reflect (Table 8, Figure 6).

The transition state of the rearrangement-ejection process for reactions of 4a-f with methoxide should reflect anionic character of the pentacoordinate intermediate &3. (Equation 45, p. 56).

(45) 6n 5 CH30 P CHoO— Si— CHf-Br —>rPh— Si— CHoAr Ar—

Rearrangement-displacement reactions of 4a-f and 5a-f with fluoride ion cannot be explained as simply as with methoxide. As described earlier, much attention has been given to the deviations in the Hammett plots of Figures 2-5 and the increased migratory aptitude of the para-dimethylaminophenyl group does not arise from its conversion to the para-dimethylammoniumphenyl group. It is presently proposed that attack of fluoride ion on 4a-f yields relatively tight pentacoordinate intermediates (7.1. Figure 7) whose subsequent reaction transition states (Figure 8) express the anionic character of silicon as modified by heterolytic-bond breaking in the leaving group and participative p i-electron contributions of the migratory phenyl groups. Such transition states involve more 57 extensive carbon-bromine bond cleavage and greater cationic character at C-l than those of structure (Equation 45, p56).

Figure 8. Transition States for Fluoride-induced Rearrangement- displacements of Aryl(halomethyl)diphenylsilanes Which Express Aryl Participation Processes and Cationic Cleavage.

In reactions of 4a.b with fluoride ion, electron poor phenyl groups migrate better than phenyl because their abilities to alleviate negative charge on the silicon are dominant. Such rearrangements express electronic effects in sigma bond transfer from silicon to carbon and are similar in type to those proposed earlier for methoxide-induced rearrangement-displacements of 4a.b. To be emphasized again is that the electrical effects on migratory aptitudes in the present systems are small and a principal reactivity effect is departure of halide from carbon attached to highly negative silicon. Migration of electron-rich phenyl groups therefore becomes accelerated as in Figure 8 when the carbon-bromine bonds are more 58 broken heterolytically and the transition states for rearrangement- displacement express the participative actions of their aromatic pi- electron systems. In such transition states, the para-dim eth y lam in o substituent can function as an effective electron-donor and thus result in accelerated migration of the para-dimethylaminophenyl group. CHAPTER V: STEREOCHEMISTRY OF REARRANGEMENT- DISPLACEMENTS

The Stereochemistry of Rearrangement-Displacements of f+1- (BromomethvDmethvlf 1-naphthvDsilane with Nucleophiles

The previous research of this dissertation has been concerned with the migratory aptitudes in rearrangement-displacements of halomethylsilanes with methoxide and with fluoride ion nucleophiles. These processes have been presumed to involve pentacoordinate silicanionic intermediates or transition states as illustrated in Equation 48. Study has now been made of the stereochemistry of nucleophilic attack on silicon in rearrangement-displacements of halomethylsilanes (91., Equation 48). To place this investigation in proper perspective, the principal literature and present theory of nucleophilic displacements on silicon and the previous hypotheses of the mechanisms of rearrangement-displacement of halomethylsilanes by nucleophiles will be summarized.

,1 R' R F o r R-Si-CHgX-^ Nuc—sSi— CHsX ■Nut ■CHoR1 (48) '' V_,3 -X' R3 R2 R* i:R

(flD m )

59 60

The stereochemistry of substitution reactions of optically active

silanes has received considerable study. 42 Nucleophilic displacement of chiral methyl(l-naphthyl)phenylsilanes £4. (Equation 49) results in inversion (950 or retention of configuration (95r~). The stereochemistry of these displacements is determined by the nature of the leaving group and by the nature of the nucleophile. Table 12 provides important examples of such displacement reactions of 94.

Me 1-Np

Nuc

95i inversion

Ph. Nuc'

1 -Np 24 Nuc Ph.

1 -Np

95r retention Table 12. The Stereochemistry of Substitution Reactions of Chiral Methyl(1-naphthyl)phenylsilanes (94).

inversion retention

M M l 95r Np = 1-naphthyl

X Reagent __ stereochemistry Reference

Cl OH", RO", R3Si O", EtLi Inversion 43,44 Li AIH4, Me— Li Inversion 45,44

F EtLi, R3Si O" Retention 44, 46

OMe HO , LiAIH4 Retention 47 ^M e EtLi, Retention 48

n-BuLi, Me— Li Retention 44(a)

H HO'.RO" Retention 49

Chiral silane 1-NpPhEtSi OMe was used. 62

Substitution reactions at silicon (SN2-Si ) 50 that result in inversion of configuration require nucleophilic attack from the opposite face of the leaving group, X, as in Equation 50. The nucleophile and the leaving group occupy apical positions in trigonal- bipyramidal pentacoordinate silicanions (96) and the leaving group,

X, departs apically at a 180 0 angle from which the chiral silane is attacked. The product 95i therefore has inverted stereochemistry at silicon. Inversion of configuration of £4. is favored by good nucleophiles and good leaving groups. Leaving groups derived from conjugate acids having pKas less than 6 (bromide, chloride, tosylate and acylate) generally give completely inverted products. 51

X i i Ph Me Nuc' Np "S' •Me Si -X' (50) Ph / ^ M e •Np ' 1 -Np Nu Nu

M 9 5 i

Reactions that lead to retention of configuration at silicon are favored by poor leaving groups such as alkoxide and fluoride. 4 8 Retention is favored also by hard nucleophiles where negative charge is more localized. Retention of configuration in displacements at silicon is thought to occur by one of two processes. The first involves nucleophilic attack at the same face (90°) as the leaving group, X, to give a trigonal bipyramidal structure, 97. as in Equation 51. The nucleophile occupies an equatorial position and the leaving group is in an axial position in 9J_. The leaving group cleaves directly from the axial position to give product 95r with retention of configuration at silicon. 52

Me Me

(51)

M az 95r

The second explanation stresses that nucleophiles must attack and leaving groups must leave from energetically more favorable axial positions. In this case retention of configuration at silicon is explained by pseudorotation of an initial trigonal bipyramidal intermediate, £iL (Equation 52). The nucleophile attacks from an energetically more favorable axial position 90° to the leaving group to give a pentacoordinate intermediate £JL as in Equation 52. The leaving group, X, occupies an equatorial position in structure £&, an unfavorable location for cleavage to occur. A single pseudorotation places the nucleophile in an equatorial position and the leaving group in an axial position to give ££. Upon departure of the leaving group product 95r is obtained with retention of configuration. 53 6 4 Me 3

Me pseudo^ Ph X Pfyi/.,, JL Nu' rotation Np SL ^ ‘X u Np" ' Np aS (52)

Nu SS ▼ Me

Phf#... J,. Nu Np"✓ 95r

Pseudorotation was proposed by Berry to rationalize the

unusual NMR spectra of PF 5 . 54 Pseudorotation involves axial- equatorial exchanges of the fluorine ligands in PF 5 , a trigonal bipyramidal species. The pseudorotation mechanism had subsequently been extended to explain various stereochemical reactions at phosphorous. 55 It has also been offered to justify retention of configuration in substitution reactions that occur on silicon in optically active silicon compounds as now described.

A pseudorotation involves reorganization of a trigonal bipyramidal intermediate where silicon is bonded to 5 atoms and is sp^d^ hybrized (100. Equation 53). The silicon atom lies in a plane where it is bonded to three atoms (A,B and C) with relatively short lengths and angles of 120°. Atoms A-C occupy equatorial positions 65 in the pentacoordinate intermediate 100. Axial atoms D and E of the pentacoordinate intermediate lie at 90° angles above and below the equatorial plane and have relatively long bonds to silicon. A single pseudorotation involves movement of two of the equatorial ligands A and B away from each other, increase of their A-Si-B angle from

120° to 180°, and occupation of axial positions with longer bonds to silicon. At the same time the two axial atoms D and E move toward each other, decrease their D-Si-E angle from 180° to 120°, and then occupy equatorial positions along with the pivot atom C, 101.

pseudorotation (53)

E3—^ 100

It is of present interest to determine the stereochemistry of rearrangement-displacement reactions of chiral (halomethyl)silanes.

Chiral silane, (+)-(bromomethyl)methyl(l-naphthyl)phenylsilane ( 8), was chosen because it is readily prepared and is expected to undergo nucleophilic attack at silicon as in Equation 54. As discussed previously there is little evidence as to whether pentacoordinate 66 intermediates are actually formed in rearrangement-displacements of halomethylsilanes. Whatever be the mechanistic details migration of a phenyl group in Equation 54 with loss of bromide should give a product 103 with either inversion, retention or racemization of configuration. Similar scenarios can be imagined if the 1-naphthyl group in & undergoes rearrangement during displacement. It is the

intriguing possibility that 102 could undergo pseudorotation that is the driving force to this study.

Nuc Me Me ^ Np— jjj— CH2Br^UC~ 'Si CH? Br NpPh|iCH2Ph Np Ph Nuc (+) (54) Ph

a 102 103

PREPARATION OF (+WBROMOMETHYL)METHYL-l - NAPHTHYLPHENYLSILANE

(+)-(Bromomethyl)methyl(l-naphthyl)phenylsilane (£.), was preparable as now described in convenient quanities for the proposed studies. The Sommers method 56 as illustrated in Equation 55 was used to prepare chiral (+)-methyl(l-naphthyl)phenylsilane ( 108). Thus dimethoxy(methyl)phenylsilane (104) was reacted with

1-naphthylmagnesium bromide (prepared from 1-bromonaphthalene and magnesium) to give racemic (methoxy)methyl(l-naphthyl)- 67 phenylsilane (105). Alkoxy exchange was effected by reaction of 105 with (-)-menthol as catalysed by potassium hydroxide to yield a diastereomeric mixture of [(-,+)-(-)](menthoxy)methyl(l- naphthyl)phenylsilane (106). Fractional crystallization of 106 in pentane at -78°C gave (-)-[(-)-menthoxy]methyl(l-naphthyl)- phenylsilane (107) as crude crystals that were recrystallized in hexane. Reduction of 107 with lithium aluminum hydride in di-n- butyl ether gave the enantiomer (+)-l-methylnaphthylphenylsilane (108). (-)-Methyl(l-naphthyl)phenylsilane was also prepared similarly, however several recrystallizations of its menthoxysilane in ethanol were required.

OCH3 OCH3 (-)MenO ., I _nn1-NpMgBr I (-)-Menthol I f l_0CH3 i 267TH'F^1 -NP - f - ph 0£ - KOH 1 - N p - S i- P h Ph Benzene Me toluene Me

1M JLQ5 1 0 a (+,-)

(55)

fractional 0( )Men Ph crystallization , , , X- .. LiAIH4 I pentane'/-7^C <->-1 Ph' H

i QZ 1Q&, [a]23D +32.8C

Phenylmercurictribromomethane effects insertion of dibromocarbene into the silicon-hydrogen bond of (+)-methyl(l- naphthyl)phenylsilane (108) with retention of configuration^ to give (+)-(dibromomethyl)methyl(l-naphthyl)phenylsilane (109). Reaction 68 of (+)-10£ with n-butyllithium at -78 °C and then hydrogen bromide yields (+)-(bromomethyl)methyl(l-naphthyl)phenylsilane (£.,

Equation 56). 58

Me Me I PhHqCBrq. C«Hft I (♦H-Mp-jsi-H ■— q— g- g i> (+)-1-Np |>i CHBr2

Ph Ph

( 1 M ) ( i m )

(56)

Me 1. n-BuLi/EtoO I ► (+)-1-Np—Si—CH2Br 2. HBr [ Ph fi, [oc]23D +8.29 0

Reaction of (+V('bromomethyl')methvl(l-naphthvDphenvlsilane (81 with Sodium Methoxide

Reaction of chiral silane £. with sodium methoxide in dry dioxane gives the products of phenyl migration 110 and naphthyl migration 111 (Equation 57). The product of phenyl migration (+)- (benzyl)(methoxy)methyl(l-naphthyl)silane (ULQ.) is found to be optically active with a specific rotation ([a] 2 3 D) of +39.5°. The rearrangement-displacement therefore occurs with significant inversion or retention of configuration at silicon. Me OCH3 Me (57) < m I • o NaOCH3 I I 1 - N p - S r-CH2Br— j m -Np -

Ph CH3 OCHa [a]23D+8.29° [a]23D+39.5° stereochem istry Q undetermined & U_Q 111

The structure of 110 was verified by independent synthesis of racemic benzyl(methoxy)methyl(l-naphthyl)silane (1141 as in Equation 58. Thus reaction of methyltrimethoxysilane with 1-

n a p h t h y 1 m a g n e s i u m bromide gave 1 - naphthylmethyldimethoxysilane (1131 which was converted by benzylmagnesium chloride to racemic 114. The *H NMR, infrared, and mass spectral analyses of 110 and 114 are identical and the carbon and hydrogen analyses of 114 are consistent with the assigned structure.

Me (58) MeSi(OMe)3- — — ► (1-Np)MeSi(OMe)2PhCH2MS£ l1 -Np— p — CH2Ph

OCH3

h e u a 114

The product of naphthyl migration, (methoxy)methyl(l- naphthylmethyl)phenylsilane ( 1111. was initially assigned by NMR upon column chromatography of the reaction mixture (Equation 57). The ratio of 110 and 111 in the reaction product (Equation 57) as determined by NMR is 10.5/1. Silane 110 was then cleanly separated by silica gel chromatography. An authentic sample of racemic 111 was prepared from dimethoxy(methyl)phenylsilane 70 ('104') and 1-naphthylmethylmagnesium chloride as in Equation 59. The lH NMR, infrared, mass spectral and the combustion analyses of 111 agree with the structural assignment.

PhMeSi(OMe)2 + 1-NpCH2MgCI------►- Ph— {j>i— CH2 (1 -Np) (5 9 ) OMe 1 M 111

Configuration of (+l-Benzyl(methoxylmethyl-l-naphthylsilane (1101

The stereochemistry of phenyl migration in the rearrangement-displacement of 3. (Equation 57) was determined by establishing the configuration of (+)-benzyl(methoxy)methyl-l- naphthylsilane (liH) as in Equation 60. Reaction of methoxysilane 110 with phenyllithium in diethyl ether gave the product of methoxide displacement, (-)-(benzyl)methyl( 1 - naphthyl)phenylsilane (1161 having [a]23D -5.25°. It is well established that chiral alkoxysilanes react with simple alkyllithium and aryllithium reagents with retention of configuration, examples and references of which were presented in Table 12. The stereochemistry of methoxide displacement of 110 by phenyllithium therefore is assumed to occur with retention of configuration. Correlation of 116 with 8. was accomplished by converting (+)- (bromomethyl)methyl( 1-naphthyl)phenylsilane (fL) with phenylmagnesium bromide in the presence of copper iodide to (+)- (benzyl)methyl(l-naphthyl)-phenylsilane (115. [a]23D +6.15°). Since no silicon-carbon bonds are broken in the Grignard coupling reaction 7 1 of 8., 115 is formed with retention of configuration. Upon comparing the signs and rotations of products 115 and 116 it is concluded that methoxide induced rearrangement-displacement of 8 occurs with predominant inversion (93%) of stereochemistry at silicon.

Me OMe NaOCH3 1 - Np— ^ i—CH2Br Dioxane 1 - Np— i—CH2Ph Ph Me [a ]23D + 8.29° [a]23D + 39.5° a 1LQ (60) PhLi retention PhMgBr/Et20 retention Cul Et20

Me I r 1 - N p— Jj5 i— CH2Ph 1 - N p— ^ i— CH2Ph

Ph Me [a]23D+ 6.15° [a] D - 5.25° 115 113.

Further proof of the stereochemical assignments is derived from the literature sequence 59 in Equation 61. Chlorination of the silyl hydride (+)-methyl(l-naphthyl)phenylsilane (1081 has been found to give (-)-(chloro)methyl(l-naphthyl)phenylsilane (117) with retention of configuration. Reaction of chlorosilane 117 with benzyllithium or benzylsodium yields (-)-benzylmethyl(l- naphthyl)phenylsilane (1161 with inversion of configuration at silicon. Conversion of 108 to 116 as in Equation 61 therefore occurs 72 with a single inversion at silicon. Clearly, 108 is converted to 115 as in Equation 62 with total retention.

Me Me Me I Cl, I PhCH2Li I 1-Np-Si-H — HjH-Np-si-ci ■—f PhCH-fi-1-NP

Ph L PhCH2Na ^ (61, inversion [a ]23D + 33.2° [a ]23D -6.22° [ a ] 23D -6 .6 8 ° iofl i12 m

Comparison of the literature preparation of (-)- benzyl(methyl)(l-naphthyl)phenylsilane (116^ illustrated in Equation 61 and preparation of (+)-benzyl(methyl)(l- naphthyl)phenylsilane (1151 from this work summarized in Equation 62 supports the fact that the copper-catalyzed coupling reaction of 8. with phenylmagnesium bromide does indeed occur with retention of configuration. Also by comparison of Equation 61 with the preparation of 116 from Equation 60, further proof of inversion of configuration at silicon for the methoxide-induced rearrangement- displacement is established.

M® Me Me (62) I 1. PhHgCBr3 | PhM gBr I 1 -Np - s f-H ► 1 - N p - s i—CH2Br — ► 1 - N p - S r~CH2Ph I 2.n-BuLi, HBr | Cul | ^ retention Ph retention [a ]23D +32.8° [a ]23D +8.29° [a ]23D + 6 A s O

1 M 8. 115

Reactions of f+WBromomethvnmethvin-naphthvPphenvlsilane with Sodium Ethoxide and Sodium 2-Propoxide 73

Study of the stereochemistry of rearrangement-displacement of 8. was then extended to reactions with sodium ethoxide and sodium 2-propoxide.

Silane & reacts with sodium ethoxide in dioxane at 23 °C to give (+)-benzyl(ethoxy)methyl(l-naphthyl)silane (118). the product of phenyl migration via rearrange-displacement (Equation 63). Ethoxysilane 118 was isolated by silica gel chromatography and has an optical activity of [a ]2 3 D + 39.4° in cyclohexane. Of immediate note is that 118 as is 110 is dextrorotatory. The structure of 118 was

CH3 OCH2CH3

^lp— Si— CH2Br — NaOCH2CH3 ^ 1 . Np_ l |_ CH ph (63) | dioxane | Ph CH3 [cc]23D +8.29° [cc]23D +39.4° a U S verified by effecting ethoxy exchange of racemic 114 with ethanol as catalyzed by potassium hydroxide in toluene to give racemic 1 19 (Equation 64). The stereochemical outcome of Equation 63 was

Me Me

1 - Np— Si— CH2P h K°H— - Np— Si— CH2Ph (64) I Toluene j OCHa OCH2CH3

1 1 4 119 determined by the sequences in Equation 65. Correlation of the configuration of 1 1 8 to reveals that ethoxide-induced 74 rearrangement-displacement of occurs with 95% inversion of configuration at silicon.

Me OCH2CH3 I NaOCH2CH3 i 1 - Np— S i—CH2Br ------Dioxane 1 - N p— !j5 i—CH2Ph Ph Me [oc]23D +8.29° [a]23D + 39.4° a US PhLi (65) retention PhMgBr/Et20 retention Cul Et20

Me Ph I 1 -Np— j>i—CH2Ph 1 - N p— j> i— CH2Ph

Ph Me [a]23D + 6.15° [a]23D - 5.50° 1 1 5 n a

Silane S. also reacts with sodium 2-propoxide to yield (+)- benzyl(isopropoxy)methyl(l-naphthyl)phenylsilane (\ 20). Equation

6 6 ) with an optical activity of [ a ] 2 3 D +28.13°.

ch 3 OCH(CH3)2 NaOCH(CH3)2 1-Np— !j>j— CH2Br 1 -Np— |>i— CH2Ph <66) dioxane Ph CH3 [a]23D +8.29° [a]23D +28.1°

a 120

The racemic analog, 121. of ethoxysilane 120 was prepared independently from methoxysilane 1 14 and 2-propanol in the 75 presence of a catalytic amount of potassium hydroxide in toluene (Equation 67). The correlation sequences in Equation 68 established

Me Me I , -Np— Si— CH2Ph HOCH(CH3)2,cat.KOH: •1 - Np— 13‘—CH2Ph (67) | Toluene OCH3 OCH(CH3)2 111 121

that rearrangement-displacement by 2-propoxide as in Equation 66 involves high order inversion (95%) of configuration.

Me I r 1 - N p— i—CH2Ph 1 - N p— i— CH2Ph

Ph Me [oc]23D +6.15° [a]23D - 5.57° 115 n e

The stereochemical results for reactions of 8. with sodium methoxide at 23 °C and 0 °C, with sodium ethoxide at 23 °C and with sodium 2-propoxide at 23 °C are summarized in Table 13. 76

Table 13. Stereochemistry of Alkoxide-induced Rearrangement- displacements of (+)-(Bromomethyl)methyl(1-naphthyl)- phenylsilane (S).

Me CR Ph 1 NaOR I 1 - Np— fj>i—CH2Br ------*M-Np— fj>f—CH2Ph Ph-U^ 1 -Np—S i—CH2PI inversion retention | Ph Me Me a A B

Predominant NucleoDhile ra123D A Tal23D B Stereochemistrv

CH30725°C +39.5° -5.25° inversion CH3O70oC +38.8° inversion CH3CH20725°C +39.4° -5.50° inversion (CH3)2CH0725°C +28.1° -5.57° inversion

The inversions of configuration for phenyl migrations in reactions of alkoxides with £. establish that the nucleophiles attack from the face opposite the phenyl group via pyramidal (pentacoordinate) trigonal processes as illustrated in Equation 69. In 122 the alkoxy and the phenyl groups are axial and the 1-naphthyl, methyl and bromomethyl groups are equatorial. Expulsion of bromide with migration of the phenyl group from the side opposite to alkoxide therefore results in products 123 with inversion about silicon. The overall process is equivalent to Walden inversion about silicon and corresponds to that found for rearrangement- displacement reactions for varied carbon compounds. The above experiments allow the further conclusion that pseudorotation is insignificant under the conditions presently investigated for rearrangement-displacements of Pseudorotation might be operational at lower temperatures or upon rearrangement- displacements of 8. with other nucleophiles.

Ph Ph

a 122 12 3

In the stereochemical investigations of rearrangement- displacements of 8. with alkoxides, phenyl was found to migrate rather than 1-naphthyl. A migratory aptitude study, similar to those in Chapter 2 of this work, was then made of reactions of with sodium methoxide in dioxane as summarized in Equation 70. CH3O— ^ i— CH2Ph -Biy r Me CH3 Ph a a H Q 1-Np— Si— CH2b £ ! ^ (70) Ph Mel-Np "Ns?-b>^ rh 124 a CH3O— ^ i— CH 2 (1 -Np)

Me 1 1 1

Direct measurements of 110 and 111 in the reaction products do not give reliable migratory aptitudes because of the susceptibilities of 110 and 111 to attack by methoxide. As with earlier methodology tetrabutylammonium fluoride was added after the starting material had disappeared. The migratory aptitude was then determined from the toluene (7 81 and 1-methylnaphthalene (127. Equation 71) formed. A migratory ratio of phenyl to 1-naphthyl of 9.5/1 (Ph/1 - Np) was found by gas chromatographic analyses of 23. and 127 using internal standard methodology. The migratory aptitude results support the earlier NMR findings that the 1-naphthyl migration product (Equation 57) from reaction of 8. and methoxide is small. 79

TBAF Si— OCH 3 + (H20) Me Me 1 1 5 125 Z5 (71) Ph Ph c h 3 I I CH30-f-CH2(1-Np) — F— Si— OCH 3 +

Me Me 127 111 125

It was then of interest to determine the stereochemistry of fluoride-induced rearrangement-displacements of 8_. Fluoride ion might be expected to attack £_ at the silicon atom to give the pentacoordinate silyl anion structure 128. Collapse of this intermediate by phenyl migration from silicon to carbon with loss of bromide should give benzyl(fluoro)methyl(l-naphthyl)silane (1291

CH 3

F - ^ C H 2Br F Jjli CF^Ph (72)

Ph 1 -Np Ph 1 -Np [a]23D +8.29°

(5) ( 1 2 5 ) (125)

The behavior of 8. with cesium fluoride in tetrahydrofuran at 23 °C was first investigated as summarized in Equation 73. The product of interest, benzyl(fluoro)methyl(l-naphthyl)silane (1291 80 was not isolated. After filtration and concentration, the crude reaction product was treated with phenyllithium. The benzyl(methyl)(l-naphthyl)phenylsilane (1301 isolated by silica gel chromatography was optically inactive.

ch 3 ch 3 CH3 (73) I CsF i 1-Np— Si— CHoBr----- >*1-Np— Si— CH2Ph i Ph Ph [

(fi) (129) (IM)

The lack of optical activity in 130 indicated it was important to determine the optical properties of 129 (Equation 73). Chiral silane £. was then reacted with cesium fluoride in tetrahydrofuran to give 129 after isolation by silica gel chromatography. Fluorosilane 129 is unstable to long exposure to silica gel and thus was eluted rapidly from the chromatographic column. The fluorosilane isolated, 129. was optically inactive inactive however. To verify its structure, 129 was prepared from benzyl(methoxy)methyl(l-naphthyl)silane (1141 and boron trifluoride-etherate (Equation 74).

CH3 ?h3 BF3-Et20 (74) OCBj F

114 129

From the above experiments of 8. with cesium fluoride, it could not be concluded as to whether racemization of 129 occurs during 8 1 or/and after its formation, or whether fluoride ion was racemizing 8.. Four experiments (A-D, Table 14) were then conducted with ,8. in tetrahydrofuran in which the equivalents of tetrabutylammonium fluoride were varied. The optical rotations of each reaction mixture diluted to one ml in tetrahydrofuran are recorded in Table 14. As the data illustrate as the amount of fluoride added is increased, the observed optical rotations of the reaction mixtures are decreased. It is clear that the reaction mixtures of 8. and tetrabutylammonium fluoride, even with only 0.25 equivalent of the fluoride source, and no work-up of the product, lose optical activity. Reaction mixture A has only approximately 18% of its optical activity and, after separation on silica gel and *H NMR analysis of the products, contains starting material 8. and fluorosilane 129 in a 0.38 ratio (8/129U Since .8. and 129 have similar Rf values on silica gel they were isolated as a mixture. Isolation of reaction mixture D in which fluoride was used in only 0.25 equivalents amount, showed approximately 69% of its optical activity and consisted of g. and 129 in a 5.69 ratio.(g/JL2£). Using NMR methods the observed optical rotation in D was found to be due to unreacted starting material g.. It is emphasized that the above ratios g. to 129 do not totally describe the reactions of 8. with fluoride ion because there is loss of 1 2 9 during chromatography and by cleavage with fluoride ion. No matter what the details of reactions of 8. and with fluoride ion, it is logical to assume that (much of) the observed optical rotations in the systems in Table 14 are due to unreacted chiral 8. 82 Table 14. Reactions of (+)-(Bromomethyl)methyl(1-naphthyl)phenylsilane (S.) with Varied Amounts of Tetrabutylammonium Fluoride.

Ph F [a ]23D + 8 .2 9 ° & 129

mmole silane ml 1 M TBAF added3 Observed Rotation6

A. 0.184 0.18(1eq) +0.083 B. 0.186 0.14(0.75eq) +0.102 C. 0.182 0.091(0.50 eq) +0.197 D. 0.184 0.046(0.25eq) +0.320 F. 0.0979 0 .00(0.Oeq) +0.245

*(a) All solutions were diluted to 1ml; (b)Optical rotations were all obtained of the reaction mixtures in tetrahydrofuran at a total volume of 1 ml.

A further attempt to obtain 129 with optical activity was made by treating silane [a]23D +8.29° in cyclohexane, with one equivalent of tetrabutylammonium fluoride in tetrahydrofuran for 10 seconds at room temperature. The solution was immediately diluted with hexane at -78 °C, followed by filtration of insoluble salts. Rapid removal of tetrabutylammonium fluoride and tetrabutylammonium bromide (by-product) was attempted in order to stop potential racemization of 12 9 by soluble salts. Chromatography on silica gel and isolation gave a mixture of initial 8. 83 and fluorosilane 129 and the mixture had an observed optical rotation of + 0.100° in cyclohexane. On the basis of NMR analysis the optical activity of the product isolated was concluded to be due to unreacted starting material 8..

It is still not clear when racemization occurs in fluoride induced-rearrangement-displacement reactions of £_• Two possibilities remain: (1) racemization of fluorosilane product 129 by either fluoride ion or by by-product bromide salt and (2) racemization in pentacoordinate intermediate 128 (Equation 72) via multiple pseudorotations before rearrangement. It is clear that fluoride (as well as methoxide) ion does not racemize the starting material 8. since 8. is isolated from reaction mixtures with no loss of optical activity. This study is worthy of further experimentation at lower temperatures and using rapid NMR methods to detect reaction intermediates.

1 -Np

P - S i — CH2Ph

1 -Np— s i— CH2Br 84

The migratory aptitudes of phenyl and 1-naphthyl groups in fluoride-induced rearrangement-displacements of & (Equation 75) were then determined by methodology similar to that described in Chapter 2. In reactions of & with two equivalents of fluoride ion the initial products of rearrangement-displacement Equation 75 react with a second equivalent of fluoride to give, upon protonation, toluene (781 and 1-methylnaphthalene (127. Equation 76). Analyses of 28. and 127 reveal that phenyl migrates faster than 1-naphthyl (Equation 75) by a factor of 11.1/1 (phenyl/1-naphthyl). This result is similar to that found in Equation 70 for methoxide-induced rearrangement-displacements of 8.. A likely reason in both cases for preferential phenyl migration is the greater bulk of the 1-naphthyl group.

TBAF

Me Me 129 133 1 3 (76)

TBAF

Me Me 122 134 121 85

Reaction of benzyl(fluoro)methyl(l-naphthyl)silane (129) with fluoride ion gave a quantitative yield of toluene (78. Equation 77). This indeed shows that the proposed benzyl(fluoro)methyl-(l- naphthyl)silane (129) product of reaction of 8. with one equivalent of fluoride can react with a second equivalent of fluoride to yield toluene (78) upon protonation of the cleaved benzyl anion.

1-Np 1 -Np 2.1 eq TBAF I - ►F-Si-F + (77) I Me Me 129 13 CHAPTER VI: SUMMARY

Aryl(bromomethyl)diphenylsilanes (4) and aryl(iodomethyl)- diphenylsilanes (5_) react with fluoride or methoxide ions by attack on silicon with rearrangement and displacement of halide to give aryl(benzyl)(fluoro)phenylsilanes and (arylmethyl)(fluoro)- diphenylsilanes or aryl(benzyl)(methoxy)phenylsilanes and (arylmethyl)(methoxy)diphenylsilanes, respectively. The products can be analyzed quantitatively by cleavage with a second equivalent of the nucleophilic reagent in a protic environment to give toluene and arylmethanes. Study has now been made of the migratory aptitude in nucleophilic rearrangement-displacements of 4 and 5. in which the aryl groups contain p-CF 3 ,p-CI, p-H, P-CH 3 , P -O C H 3 and p-

N(CH 3 )2 substituents.

The migratory aptitudes of varied phenyl groups in reactions of 4 (23 °C, 0 °C and -20 °C) and £ (23 °C) with tetrabutylammonium fluoride in tetrahydrofuran are P-CF 3 -C 6 H 4 > p -C l-C 6 H 4 > p-(C H 3 )2 N -

C 6 H 4 > P -C H 3 O-C 6 H 4 ~ P-C H 3 -C 6 H 4 ~ C6 H 5 . The logarithms of the relative migratory aptitudes when plotted against sigma-zero substituent values give curved free-energy correlations. Rearrangement-displacement reactions of 4 with methoxide at 23 °C

86 87 give however migratory aptitudes in the order P-CF 3 -C 6 H 4 > p -C l-

C 6 H 4 > C6 H 5 > P-C H 3 O-C 6 H 4 > P-C H 3 -C6 H 4 > p-(CH3)2N-C6H4. A Hammett plot of the aryl migratory aptitudes for methoxide induced reactions of 4 gives a linear correlation (correlation coefficient = 0.97) with a rho value of 0.72. This suggests that substituents that can better accommodate negative charge in the transition state will migrate faster. The difference in the fluoride and methoxide processes is proposed to be due to electrical effects in pentacoordinate rearrangement-displacement transition states.

Reactions of chiral (+)-(bromomethyI)methyl(l-naphthyl)- phenylsilane QL) with alkoxide ions (methoxide, ethoxide and 2- propoxide) yield (alkoxy)benzylmethyl(l-naphthyl)silanes. The stereochemistry of the rearrangement-displacements occur with high order inversion of configuration at silicon. Inversion is proposed to be due to alkoxide attack on silicon, opposite to the phenyl substituent, followed by migration of the phenyl substituent at the side opposite of methoxide. Reactions of cesium fluoride or tetrabutylammonium fluoride with £_ give racemic (benzyl)(fluoro)methyl(l-naphthyl)silanes. It is not clear however as to the causes of the racemizations. CHAPTER VII: EXPERIMENTAL

General Procedures

Reactions were generally conducted in oven dried glassware under dry argon. Migratory aptitude studies were performed in sealed sample vials. Gas chromatographic yields were determined by using internal standard methods and peak areas are corrected for response factors of the flame ionization detector.

Gas Chromatography

Gas chromatographic analyses were accomplished on a Hewlett Packard 5890A Gas Chromatograph equipped with a flame ionization detector. A gas flow mixture of helium (40 psi), air (40 psi), and hydrogen (19 psi) was used with the head pressure at the column set at 4 psi. The capillary column, RSL-300, was purchased from Research Separations Laboratories and consisted of a 15 m x 0.53 mm bonded FSOT and a polyphenylmethylsiloxane 1.2 um stationary phase. The integrator was a Hewlett Packard 3396A unit with a chart speed of 1 cm per minute. Gas chromatographic yields were determined using internal standard techniques and corrected for detector response. This method gives product yields accurate to approximately + 5% of the absolute value. 60

88 89

Infared Spectra

Infrared spectra were obtained on a Perkin Elmer 1600 Series Fourier Transform Infrared Spectrometer. Infrared spectra of solids were obtained using potassium bromide pellets. Spectra of liquids or oils were obtained neat on sodium chloride plates. Absorption peaks are reported in cm _1.

Nuclear Magnetic Resonance

Proton nuclear magnetic resonance (NMR) spectra were obtained with a Bruker 250 MHz nuclear magnetic resonance spectrometer. All spectra were obtained in deuterated chloroform. Proton peaks are reported in parts per million using chloroform resonance at 7.26 ppm as the standard.

Mass Spectra

Mass spectra were performed on the DS-55 Mass Spectrometry Data System by C. Weisenberger using electron ionization. 90

Elemental Analysis

Carbon and hydrogen combustion analyses were performed by Atlantic Microlab, Inc., Norcross, Georgia.

Melting Points

Melting points were obtained on a Thomas Hoover Uni-melt capillary melting point apparatus and are uncorrected.

Optical Rotations

Optical rotations were obtained using a Perkin Elmer 241C Polarimeter with a 1-dm cell. The measurements were obtained using Na/cont light (589 nm) at 23 °C. 9 1 Preparation of Diphenyl('4-trifluoromethvlphenvDsilane (63a)

To a stirred solution of 5.0 grams (0.022 mole) of 4-bromobenzotrifluoride in 28 ml of dry ether under argon at -40 °C was added 8.9 ml (2.5 M in hexane, 0.022 mole) of n-butyllithium over 15 minutes. The solution was stirred for 10 minutes, warmed to room temperature, transferred dropwise to a solution of 6.3 grams (0.025 mole) of dichlorodiphenylsilane (611 in 20 ml of dry ether and

refluxed for 8 hours. The ether was removed by distillation while

adding 1 0 0 ml of dry benzene until the stillhead temperature reached 78 °C. The benzene solution was filtered and the benzene

was removed at reduced pressure to give 11.0 grams of an orange oil that was immediately dissolved in 40 ml of dry ether and added at 0 °C to 0.60 gram (0.016 mole) of lithium aluminum hydride in 20 ml of ether and the mixture was refluxed overnight. The excess lithium aluminum hydride was carefully quenched at 0 °C with ether saturated with water and the mixture was then treated with 45 ml of 10% acetic acid. The organic layer was separated and washed with 50 ml of 10% acetic acid, 50 ml of water and 50 ml of brine, and dried over sodium sulfate. The solution was filtered and fractionally distilled to give 5.1 grams (0.016 mole, 70% yield) of diphenyl(4- trifluoromethylphenyl)silane (63a.): bp 145-150 °C , 0.05 torr; *H

NMR (CDCI3 ) 5.50 (s, 1H, Si-H) , 7.3-7.7 (m, 14H, Si-Ar-H).

Preparation of M-ChlorophenvPdiphenvlsilane f63bl 92

To a stirred mixture of 2.67 grams (0.111 mole) of magnesium in 30 ml of dry ether was added dropwise (30 minutes) 19.2 grams (0.10 mole) of 4-bromochlorobenzene in 20 ml of dry ether. After

the addition was complete, the solution was heated for 1 hour and then cooled to room temperature. The Grignard reagent was added dropwise over 10 minutes to 25.3 grams (0.10 mole) of dichlorodiphenylsilane (61 ) in 62 ml of dry ether. The solution was refluxed for 24 hours after which the ether was removed by distillation while adding 150 ml of dry benzene until the stillhead temperature reached 78 °C. The solution was filtered and the benzene evaporated at reduced pressure to leave a yellow oil that was immediately dissolved in 150 ml of dry ether and added to 2.3 grams (0.060 mole) of lithium aluminum hydride in 50 ml ether at 0 °C and the mixture was refluxed for 4 hours. The excess hydride was carefully quenched at 0 oC with ether saturated with water and the mixture was then treated with 60 ml of 10% acetic acid. The ether layer was separated and washed with 60 ml of 10% acetic acid, 60 ml of water and 60 ml of brine, and dried over sodium sulfate. The solution was filtered and fractionally distilled to give 12.0 grams (0.0408 mole, 41% yield) of (4-chlorophenyl)-diphenylsilane (63b):

160-165 oC bp 0.10 torr, lit .27 161-162 oc 0.10 torr; lH NMR (CDCI 3 )

5.49 (s, 1H, Si-H) , 7.25-7.60 (m, 14H, Si-Ar-H).

Preparation of (4-Methvlphenvl)diphenvlsilane (63d) 93

To 1.5 grams (0.22 mole) of finely cut lithium metal in 33 ml of dry ether was added dropwise 17.1 grams (0.10 mole) of 4- bromotoluene in 133 ml of dry ether over 30 minutes and the mixture was refluxed overnight. The lithium reagent was added to 25.3 grams (0.10 mole) of dichlorodiphenylsilane (61 i in 75 ml of dry ether and the solution was refluxed for 2 hours. The ether was removed by distillation while adding 150 ml of dry benzene until the stillhead temperature reached 78 °C. The solution was filtered and the benzene evaporated at reduced pressure. The brown oil residue was dissolved in 150 ml of ether and added to 2.27 grams of lithium aluminum hydride in 50 ml of ether at 0 °C and the mixture was

refluxed 6 hours. Excess hydride was carefully quenched at 0 °C with ether saturated with water and the resulting mixture was treated with 70 ml of 10% acetic acid. The organic layer was separated and washed with 70 ml of 10% acetic acid, 70 ml of water and 70 ml of brine and dried over sodium sulfate. The solution was filtered and fractionally distilled to give 15.3 grams (0.056 mole, 56% yield) of (4-methylphenyl)diphenylsilane (63lL): bp 148-153 °C at

0.05 torr, lit.2? 147-148 °C 0.2 torr; *H NMR (CDCI 3 ) 2.41 (s, 3H, Si-

A r-C H 3 ) , 5.51 (s, 1H, Si-H) , 7.23-7.26 (d, 2H, H ortho to methyl) ,

7.34-7.65 (m, 12H, Si-Ar-H).

Preparation of ^-Methoxvphenvlldiphenvlsilane (63e )

To a flame dried round bottom flask under argon and equipped with a stir bar was added 2.67 grams of magnesium and 25 ml of 94 ether. To the stirred mixture was added over 30 minutes 18.7 grams (0.10 mole) of 4-bromomethoxybenzene in 20 ml of ether. The solution was refluxed 30 minutes after addition was complete and the Grignard reagent was then added dropwise to 25.3 grams (0.10 mole) of dichlorodiphenylsilane (61 ) in 62 ml of dry ether and the mixture was refluxed over a weekend. The ether was removed by distillation while adding 150 ml of benzene until the stillhead temperature reached 78 °C. The solution was filtered and the benzene removed at reduced pressure to give an oil that was dissolved in 150 ml of ether and added to 2.27 grams of lithium aluminum hydride in 50 ml of ether at 0 °C and the mixture was refluxed overnight. Excess lithium aluminum hydride was carefully quenched at 0 °C with ether saturated with water and the mixture was treated with 60 ml of 10 % acetic acid. The ether solution was

separated and washed with 60 ml of 1 0 % acetic acid, 60 ml of water and 60 ml of brine and dried over sodium sulfate. The ether solution was filtered and fractionally distilled to give 15.3 grams (0.0545 mole, 55% yield) of (4-methoxyphenyl)diphenylsilane ((He): bp 176-

180 oc 0.05 torr, lit.27 bp 183-184 oc 1.5 torr; lH NMR (CDCI3 ) 3.80 (s, 3H, Si-Ar-OCHj) , 5.45 (s, 1H, Si-EL) , 6.90-6.94 (d, 2H, ortho H to methoxy) , 7.31-7.59 (m, 12H, Si-Ar-H).

Preparation of (p-Dimethvlaminophenvndiphenvlsilane (630

To a stirred solution of 10 grams (0.05 mole) of p- bromo(dimethylamino)benzene in 66 ml of dry ether under argon at -40 °C was added 20 ml (0.05 mole, 2.5 M) of n-butyllithium over 15 minutes. The mixture was warmed to room temperature and transferred dropwise in 15 minutes to 12.7 grams (0.05 mole) of dichlorodiphenylsilane (£1) in 45 ml of ether and the solution was refluxed for 24 hours. The ether was removed by distillation while adding 100 ml of benzene until the stillhead temperature reached 78 °C. The solution was filtered and the benzene was evaporated at reduced pressure to give a blue oil that was dissolved in 75 ml of ether and added to 1.15 grams (0.030 mole) of lithium aluminum hydride in 25 ml of ether at 0 °C. After the mixture had been refluxed for 4 hours, the excess lithium aluminum hydride was carefully quenched at 0 °C with ether saturated with water and the resulting mixture was treated with 50 ml of 10% acetic acid. The organic layer was separated and washed with 50 ml of 10% acetic acid, 50 ml of water and 50 ml of brine and dried over sodium sulfate. The solution was filtered and fractionally distilled to give 6.0 grams (0.02 mole, 40% yield) of (4-dimethylaminophenyl)- diphenylsilane (63f): bp 185-189 °c at 0.10 torr, lit.27 186-187 oq

0.15 torr; lH NMR (CDCI3 ) 3.00 (s, 6 H, Si-Ar-N(CH3 )2 ) , 5.50 (s, 1H,

Si-H.) , 6.66-6.79 (d, 2 H, H ortho to dimethylamino) , 7.36-7.65 (m, 12H, Si-Ar-H).

Preparation of Triphenvlsilane (63c)

To a stirred suspension of 2.67 grams of magnesium and 30 ml of ether was added over 30 minutes 15.7 grams (0.10 mole) of bromobenzene in 20 ml of ether and the mixture was refluxed for 30 minutes after addition was complete. The Grignard reagent was added dropwise to 25.3 grams (0.10 mole) of dichlorodiphenylsilane (611 in 62 ml of dry ether and the mixture was refluxed overnight. The ether was removed by distillation while adding 150 ml of benzene until the stillhead temperature reached 78 °C. The solution was filtered and the benzene was removed at reduced pressure. The residue was dissolved in 150 ml of ether and added to 2.27 grams (0.06 mole) of lithium aluminum hydride in 25 ml of ether at 0 °C. After the mixture had been refluxed for 3 hours, the excess lithium aluminum hydride was carefully quenched at 0 °C with ether saturated with water and the resulting solution was treated with 50 ml of 10% acetic acid. The organic layer was separated and washed with 10% acetic acid, water and brine and dried over sodium sulfate. The ether solution was filtered and evaporated and the remaining material was fractionally distilled to give 13.0 grams (0.045 mole) of triphenylsilane (63c): bp 121-128° C at 0.05 torr, (Aldrich; bp 152 °C at 0.20 torr).

Preparation of (Dibromomethvl)diphenvl(4-trifluoromethvlphenvl)- silane (64a)

To a flame dried round bottom flask under argon was added 4.93 grams (0.015 mole) of diphenyl(4-trifluoromethylphenyl)silane (63a). 7.94 grams (0.015 mole) of phenylmercurictribromomethane and 75 ml of dry benzene. The stirred solution was heated at 85 °C 97 for 4 hours. Precipitation of phenylmercuric bromide occurred and the solution was filtered from insolubles and the benzene was removed at reduced pressure. The remaining material was dissolved in 100 ml of pentane and the insolubles were filtered. The pentane solution was evaporated at reduced pressure and the remaining material was chromatographed on silica gel using 90% hexane-10% benzene as the eluent. The product, (dibromomethyl)diphenyl(4- trifluoromethylphenyl)silane (64a)> was isolated and recrystallized in hexane to obtain 3.1 grams (0.0062 mole, 41% yield) of white crystals: mp 108-109.5 °C; lH NMR (CDCI3 ) 5.76 (s,lH, Si-CHBr 2 ) , 7.40-7.86 (m, 14H, Si-Ar-H); MS no M+ was observed, 327.0832(100,

C i 9H i 4 F 3 Si). Anal. Calcd for C 2 0 H l 5 B r2 F 3 Si: C, 48.02%; H, 3.02%. Found: C, 47.92%; H, 3.05%.

Preparation of ^-ChlorophenvOfdibromomethvlldiphenvlsilane (6 4 b )

To a flame dried round bottom flask under argon was added 5.00 grams (0.017 mole) of (4-chlorophenyl)diphenylsilane (63b). 9.00 grams (0.017 mole) of phenylmercurictribromomethane and 80 ml of dry benzene. The stirred solution was heated at 85 °C for 5 hours. After cooling, the solution was filtered free from the precipitate of phenylmercuric bromide, and the benzene was removed at reduced pressure. The remaining material was diluted with 100 ml of pentane and the insolubles were filtered. After the pentane had been removed at reduced pressure, the residue was 98 chromatographed on silica gel using 90% hexane-10% benzene as eluent. The product, (4-chlorophenyl)(dibromomethyl)- diphenylsilane (64b). was isolated and recrystallized in hexane to give 3.3 grams (0.0071 mole, 42% yield) of white crystals : mp 116.5-

118 OC; lH NMR (CDCI3 ) 5.73 (s, 1H, Si-CHBr 2 ) , 7.35-7.75 (m, 14H, Si-

Ar-H) ; MS no M+ observed, 293.0563 (100, C l 8H i 4 ClSi). Anal. Calcd

for C i9H i 5 Br2 ClSi: C, 48.90%; H, 3.24%. Found: C, 48.88%; H, 3.24%.

Preparation of (DibromomethvDtriphenvlsilane (64c)

To a flame dried round bottom flask under argon was added 4.88 grams (0.0187 mole) of triphenylsilane (63c). 8.82 grams (0.0166 mole) of phenylmercurictribromomethane and 75 ml of dry benzene. The stirred solution was heated at 85 °C for 4 hours. After cooling, the solution was filtered free of phenylmercuric bromide, and the benzene was removed at reduced pressure. The remaining material was taken up in petroleum ether and the insolubles were removed by filtration. The solvent was removed at reduced pressure and the remaining material was recrystallized three times from hexane to give 2.4 grams (0.0056 mole, 30% yield) of

(dibromomethyl)triphenylsilane (64c): mp 148-152 °C, lit .30 mp

154-156 oc; lH NMR (CDCI 3 ) 5.76 (s, 1H, Si-CH Br 2 ) , 7.37-7.73 (m, 15H, Si-Ar-H).

Preparation of (Dibromomethyl)diphenyl(4-methylphenvl)silane (64d) 99

To a flame dried round bottom flask under argon was added 3.00 grams (0.0109 mole) of (4-methylphenyl)diphenylsilane (63d). 5.77 grams (0.011 mole) of phenylmercurictribromomethane and 60 ml of dry benzene. The stirred solution was heated at 85 °C overnight. After cooling, the solution was filtered free of phenylmercuric bromide, and the benzene was removed at reduced pressure. The remaining material was taken up in 100 ml of pentane and the insolubles were removed by filtration. The pentane was removed at reduced pressure and the remaining material was chromatographed on silica gel using 90% hexane-10% benzene as the eluent. Isolation followed by recrystallization gave 2.6 grams (0.0058 mole, 53% yield) of (dibromomethyl)(4-methylphenyl)- diphenylsilane (64d): mpllO-112 OQ lH NMR (CDCI 3 ) 2.40 (s, 3H, Si-

A r-C H 3 ) , 5.75 (s, 1H, Si-CHBr2 ) , 7.22-7.25 (d, 2 H, H ortho to methyl) , 7.32-7.80 (m, 12H, Si-Ar-H).

Preparation of (Dibromomethvl,)(4-methoxyphenyl)diphenvlsilane (6 4 e)

To a flame dried round bottom flask under argon was added 3.00 grams (0.0107 mole) of (4-methoxyphenyl)diphenylsilane (63e). 5.66 grams (0.0107 mole) of phenylmercurictribromomethane and 53 ml of dry benzene. The solution was heated at 85 °C and stirred for 6 hours. After cooling, the mixture was filtered free of phenylmercuric bromide, and the benzene was removed at reduced pressure. The remaining material was taken up in 100 ml of 100 pentane, filtered and concentrated at reduced pressure. The product was chromatographed on silica gel using 90% hexane-10% benzene as the eluent (the benzene concentration was increased as elution progressed). After isolation and recrystallization from hexane 1.8 grams (0.0062 mole 58% yield) of (dibromomethyl)(4- methoxyphenyl)diphenylsilane (64eJ were obtained: mp 124-127

OC; *H NMR (CDCI 3 ) 3.84 (s, 3H, Si-Ar-OCH3 ) , 5.74 (s, 1H, Si-CHBr 2 ) , 6.94-6.98 (d, 2H, H ortho to methoxy) , 7.37-7.72 (m, 12H, Si-Ar-HJ;

MS no M+ was found, 289.1049 (100, C i 9 HnSiO). Anal. Calcd for

C2 0 H l 8Br2 OSi: C, 51.97%; H, 3.92%. Found: C, 51.84%; H, 3.88%.

Preparation of Bromomethvltrichlorosilane HO') 31

To 2000 ml of methyltrichlorosilane (69^ in a flame dried 3 liter round bottom flask under argon equipped with a dry ice condenser was added 680 grams (3.78 moles) of bromine portionwise. The solution was irradiated with a 150 watt light. After each addition of bromine, chlorine was bubbled through the solution until the dark red color of the bromine disappeared. After completion of the addition, distillation gave 160 grams of bromomethyltrichlorosilane (20): bp 135-139 °C; Iff NMR (CDCI 3 ) 3.00 (s, Si-CH?Br). The small amount of chloromethyltrichlorosilane present was removed by fractional distillation.

Preparation of Bromomethvltrichlorosilane (70*) 32 101

To a flame dried round bottom flask under argon in an ice bath was added 260 ml of ethyl bromide, 10.51 grams (0.390 mole) of aluminum foil and 175.2 grams of (chloromethyl)trichlorosilane (0.95 mole). The mixture was stirred while 30.3 ml (0.60 mole) of bromine was added slowly at 0 °C. After the vigorous reaction had subsided, the mixture was warmed to room temperature and stirred overnight. The ethyl bromide was removed by distillation and the remaining liquid was stored at room temperature during which aluminum chloride and aluminum bromide precipitated. Removal of the liquid and fractional distillation gave 146.6 grams of bromomethyltrichlorosilane (70.0.642 mole, 6 8 % yield).

Preparation of (Bromomethvllchlorodiphenvlsilane (711

To a 2 liter flame dried round bottom flask equipped with a condenser, mechanical stirrer and addition funnel was added 59.3 grams (0.26 mole) of bromomethyltrichlorosilane (701 in 250 ml of ether. A solution of phenylmagnesium bromide (0.52 mole) in ether was added dropwise over 2 hours with vigorous stirring. The mixture was refluxed for 4 hours after addition was complete. The contents were cooled to room temperature and filtered through a glass fritted funnel under argon. The ether was removed at reduced pressure and the remaining material was fractionally distilled to give 13.2 grams (0.042 mole, 17% yield) of (bromomethyl)- 102

chlorodiphenylsilane (711: bp 136-140 °C, 0.5 torr; !h NMR (CDCI 3 )

3.08 (s, 2H, Si-CH2 Br) , 7.39-7.77 (m, 10H, aryl H).

Preparation of (Bromomethvlldiphenyl(4-trifluoromethvlphenvP- silane (4al

A solution of 1.05 ml (2.5 M, 2.6 mmoles) of n-butyllithium in hexane was added dropwise over 5 minutes to 1.25 grams (2.5 mmoles) of (dibromomethyl)diphenyl(4-trifluoromethylphenyl)silane (64a.) in 48 ml of anhydrous ether at -78 °C under argon. The solution was thenstirred for 10 minutes at -78 °C and treated with gaseous hydrogen bromide for 10 seconds. The mixture was warmed to room temperature and 25 ml of water was added. The ether layer was separated, washed with brine, dried over sodium sulfate and filtered. Removal of solvent at reduced pressure gave a solid which was chromatographed on silica gel using 90% hexane-10% benzene as eluent. The solid was isolated and dissolved in 15 ml of pentane and placed in a freezer. Crystallization overnight gave 0.60 gram (1.4 mmoles, 56% yield) of (bromomethyl)diphenyl(4-trifluoromethylphenyl)silane, (4a) a white crystalline solid: mp 73-74 <>C; lH NMR (CDCI 3 ) 7.38-7.74 (m, 14H,

Si-Ar-H) , 3.20 (s, 2H, Si-CH 2 -Br); IR (KBr) 3135(w) , 3069(w) , 3049(w) , 3025(w) , 3006(w) , 2938(w) , 285l(w) , 1428(m) , 1391(m) , 1323(s) , 1172(s) , 1158(m) , 1140(s) , 1128(s) , 1116(m) , 1105(m) , 1059(m) , 1059(s) , 1016(m) , 832(m) , 754(m) , 745(m) , 730(m) , 724(s) , 724(s) , 707(m) , 698(s) , 601 (w) cm-1; MS M+

420.1286 (C 2 0 H l 6 BrF3 Si, 0.38%) , 422.0251 (C2 0 H l 6 B rF 3 Si, 0.37%) , 103 327.0878 (Ci 9 H i 4 F 3 Si, 100%). Anal. Calcd for C 2 0 H l 6 B rF 3 Si: C, 57.01%; H, 3.83%. Found: C, 57.10%; H, 3.87%.

Preparation of (Bromomethvl¥4-ch1orophenvOdiphenylsilane (410

A solution of 1.42 ml (2.5 M, 3.55 mmoles) of n-butyllithium in hexane was added in 5 minutes to 1.58 grams (3.39 mmoles) of (dibromomethyl)(4-chlorophenyl)diphenylsilane (64b) in 70 ml of anhydrous ether at -78 °C under argon. The mixture was stirred for 10 minutes at -78 °C and then treated with gaseous hydrogen bromide for 10 seconds. The solution was warmed to room temperature after which 50 ml of water was added. The ether layer was separated, washed with brine, dried over sodium sulfate, filtered and concentrated at reduced pressure. The remaining oil was chromatographed on silica gel using 90% hexane-10% benzene as eluent. Isolation and recrystallization from hexane gave 0.88 gram (2.3 mmoles, 67% yield) of (bromomethyl)(4-chlorophenyl)- diphenylsilane (4b): mp 76-77 °C; lH NMR (CDCI 3 ) 7.35-7.58 (m,

14H, Si-Ar-H) , 3.16 (s, 2H, Si-CH 2 Br) ; IR (KBr) 3066(m) , 2923(m) ,

1910(m) , 1823(w) , 1651(w) , 1574(s) , 1553 (m) , 1484(s) , 1454(w) , 1427(s) , 1381(s0 , 1339(m) , 1305 (m) , 1264(w) , 1187(m) , 1158(w) , llll(s) , 1083(s) , 1013(s) , 996(m) , 853(w) , 813(s) , 790(s) , 763(s) , 734(s) , 698(s) cm-1; MS M+ 387.9903

( C l 9H i 6 BrClSi, 0.36%) , 385.9969 (Cl 9H i 6 BrClSi, 0.73%) , 293.0648

( C l 8H i 4 ClSi, 100%). Anal. Calcd for C i 9H i 6 BrClSi: C, 58.85%; H,

4.16%. Found: C, 58.78%; H, 4.14%. 104

Preparation of (Bromomethvl¥4-methvlphenvPdiphenvlsi1ane (4cO

A solution of 1.05 ml (2.5 M, 2.63 mmoles) of n-butyllithium in hexane was added dropwise in 5 minutes to 1.07 grams (2.40 mmoles) of (dibromomethyl)(4-methylphenyl)diphenylsilane (64dl in 47 ml of anhydrous diethyl ether at -78 °C under argon. The mixture was stirred for 10 minutes at -78 °C, treated with gaseous

hydrogen bromide for 10 seconds, warmed to room temperature and 30 ml of water was added. The ether layer was separated, washed with brine, dried over sodium sulfate, filtered and concentrated at reduced pressure. The residue was dissolved in hexane in which moderately brown crystals formed. The crystals were chromatographed on silica gel using 90% hexane-10% benzene as eluent. After isolation and recrystallization from hexane, 0.40 gram (10.9 mmoles, 45% yield) of (bromomethyl)(4- methylphenyl)diphenylsilane (4d) was obtained: mp 63.5-65.5 °C;

lH NMR (CDCI3 ) 7.35-7.61 (m, 12H, Si-Ar-H), 7.20-7.35 (d, 2H, H

ortho to methyl) , 2.38 (s, 3H, Si-Ar-CH3 ) , 3.18 (s, 2H, SiCHoBrl: IR (KBr) 3065(m) , 3021(w), 2931(w) , 1818(w) , 1654(w) , 1599(w) , 1587(w) , 1566(w) , 1499(w) , 1486(w) , 1443(w) , 1426(w) , 1394(w) , 1382(w) , 1382(w) , 1325(w) , 1313(w) , 1259(w) , 1192(w) , 1155(w) , 1108(s) , 1029(w) , 997(w) , 916(w) , 846(w) , 804(w) , 742(s) , 723(s) , 698(s) , 674(w) , 614(w) cm-1 ; MS M+

366.0467 (C 2 0 H l 9 BrSi, 0.41%) , 368.0436 (C 2 Q H l9 BrSi, 0.38%) , 105 273.1112 (Ci 9H nSi, 100%). Anal. Calcd for C 2 0 H l 9BrSi: C, 65.39%;

H, 5.21%. Found: C, 65.48%; H, 5.27%.

Preparation of ('Bromomethvl¥4-methoxvphenvndiphenvlsilane (4e^

A solution of 0.9 ml (2.5 M, 2.30 mmoles) of n-butyllithium in hexane was added dropwise over 5 minutes to 1.00 gram (21.6 mmoles) of (dibromomethyl)(4-methoxyphenyl)diphenylsilane (64e) in 45 ml of anhydrous ether at -78 °C under argon. The solution was stirred for 10 minutes at -78 °C and then treated with gaseous hydrogen bromide for 10 seconds. Argon was bubbled through the mixture for 5 minutes at -78 °C. The solution was warmed to room temperature and 50 ml of water was added. The ether extract was separated, washed with brine, dried over sodium sulfate, filtered and concentrated at reduced pressure to a brown oil which was chromatographed on silica gel using 90% hexane-10% benzene as the eluent (the benzene concentration was increased as the elution progressed). Isolation and recrystallization from hexane gave 0.32 gram (0.834 mmole, 39% yield) of (bromomethyl)(4- methoxyphenyl)diphenylsilane (4el: mp 65-66.5 °C; NMR

(CDCI3 ) 7.35- 7.60 (m, 12H, Si-Ar-H) , 6.93-6.96 (d, 2H, H ortho to methoxy) , 3.83 (s, 3H, CH3-0-Ph-Si) , 3.17 (s, 2H, Si-CH&Br); IR (KBr)

3126(w) , 3083(w) , 3063(w) , 3015(s) , 2995(w) , 2965(m) , 2926(m) , 2838(m) , 1592(s) , 1564(m) , 1533(m) , 1503(s) , 1485(m) , 1461(m) , 1442(m) , 1427(s) , 1397(m) , 1378(w) , 1310(w) , 1280(s) , 1250(s) , 1183(s) , 1112(s) , 1029(s) , 996(m) , 829(m) , 106 819(m) , 798(m) , 732(s) , 720(s) , 700(s) , 672(m) cnr*; MS M+

382.0357 (C 2 0 H l 9 BrOSi, 1.80) , 384.0341 (C2 0 H l 9 BrOSi, 1.86) ,

289.1029 (Ci9HnOSi, 100). Anal. Calcd for C 2 0 H l 9BrOSi: C, 62.66%; H, 5.00%. Found: C, 62.47%; H, 5.03%.

Preparation of (Bromomethvnf4-dimethvlaminophenyPdiphenvl- silane (4f)

To 0.25 gram (0.10 mole) of magnesium in 5 ml of anhydrous tetrahydrofuran was added with stirring 1.96 grams (9.8 mmoles) of 4-bromo(dimethylamino)benzene in 10 ml of tetrahydrofuran over 30 minutes. The solution was stirred for 2 hours and then transferred to a mixture of 3.05 grams (9.8 mmoles) of (bromomethyl)chlorodiphenylsilane (7 1 'i in 15 ml of tetrahydrofuran. The resulting solution was stirred 8 hours followed by solvent removal at reduced pressure. The remaining material was taken up in 100 ml of ether and 50 ml of water and the organic layer was separated, washed with brine and dried over sodium sulfate. After filtration and ether removal at reduced pressure, the resulting oil was chromatographed on 150 grams of silica gel using 98% hexane-2% ethyl acetate as eluent. Isolation of the product and recrystallization from hexane gave 1.62 grams (0.0041 mole, 41% yield) of (bromomethyl)(4-dimethyl-aminophenyl)diphenylsilane

(4f): mp 105-107 <>C; lH NMR (CDCI 3 ) 7.33-7.62 (m, 12H, Si-Ar-H) , 6.72-6.75 (d, 2H, H ortho to dimethylamino) , 3.16 (s, 2H, Si-CH?-Br) ,

2.99 (s, 6 H, (C H 3 ) 2 N); IR (KBr) 3085(w) , 3065(w) , 3050(w) ,

301 l(w) , 2996(w) , 2924(w) , 2888(w) , 2852(w) , 2809(w) , 1594(s) 107 , 1538(m) , 1516(s) , 1485(w) , 1441(m) , 1426(s) , 1403(m) , 1377(m) , 1363(s) , 1324(w) , 1305(w) , 1280(w) , 1262(w) , 1229(m) , 1209(s) , 1191(w) , 1113(s) , 1065(w) , 1053(w) cm-1; MS

M+ 395.0722 (C 2 l H 2 2 BrNSi, 10.36%), 397.0693 (C 2 l H 2 2 B rN S i,

10.67%) , 302.1412 (C 2 0 H2 0 NSi, 100%). Anal. Calcd for C 2 lH 2 2 BrNSi:

C, 63.63%; H, 5.59%. Found: C, 63.48%; H, 5.64%.

Preparation of (Bromomethvl)triphenvlsilane (4c)

A solution of 1.53 ml (2.5 M, 3.8 mmoles) of n-butyllithium in hexane was added in 5 minutes to 1.50 grams (3.47 mmoles) of (dibromomethyl)triphenylsilane (64c) in 70 ml of anhydrous tetrahydrofuran at -78 °C under argon. The solution was stirred for 10 minutes at -78 °C and then treated with gaseous hydrogen bromide for 10 seconds. The solvent was removed at reduced pressure to give a white solid which was taken up in 50 ml of ether and 50 ml of water. The ether layer was separated, dried over sodium sulfate, filtered and concentrated at reduced pressure to a viscous oil which was chromatographed on silica gel using 90% hexane-10% benzene as eluent. Isolation and recrystallization from hexane gave 0.54 gram (1.5 mmoles, 44% yield) of

(bromomethyl)triphenylsilane (4c): mp 118-120 °C lit .30 mp 121-

122 OC; lH NMR (CDCI3 ) 7.36-7.73 (m, 14H, Si-Ar-H) , 3.20 (s, 2H, Si-

CH 2 -Br). MS M+ 352.0228(Cl9 H 1 7 BrSi, 0.32%), 354.0266

( C l9H i 7 BrSi, 0.27%), 259.0962 (Cl 8H l 5 Si, 100%).

Preparation of (Iodomethvl)diphenvl(4-trifluoromethvlphenvl)silane £5al 108

A solution of 0.90 gram (2.4 mmoles) of (chloromethyl)- diphenyl(4-trifluoromethylphenyl)silane and 1.44 grams (9.6 mmoles) of sodium iodide in 2 0 ml of anhydrous acetonitrile was heated at 82 °C. Sodium chloride precipitated and heating was continued for 48 hours. The mixture was cooled to room temperature, diluted with ether, filtered and concentrated at reduced pressure. The residue was dissolved in hexane, filtered and evaporated to an oil that was chromatographed on silica gel using 90% hexane-10% benzene as eluent. Isolation after recrystallization gave 0.73 gram (1.56 mmoles, 65% yield) of (iodomethyl)diphenyl(4- trifluoromethylphenyl)silane (5aV. mp 67-68.5 °C; *H NMR (CDCI 3 )

7.37-7.74 (m, 14H, Si-Ar-H) , 2.72 (s, 2H, Si-CH 2 -I); IR (KBr) 3069(w) , 2929(w) . 2360(w) , 1961(w) , 1826(w) , 1607(w) , 1587(w) , 1486(w) , 1427(s) , 1369(w) , 1103(s) , 1059(s) , 1028(w) , 1017(m) , 997(w) , 961(w) , 855(w) , 832(s) , 781(w) , 742(s) , 730(s) , 717(s) , 703(s) , 665(w) , 600(w) cm’l; MS M+ 467.9978

(C2 0 H l 6 F3 lSi, 2.87%) , 327.0822 (Ci 9H i 4 F 3 Si, 100%). Anal. Calcd for

C20H l 6 F3 lSi: C, 51.29%; H, 3.44%. Found; C, 51.34%; H, 3.45%.

Preparation of M-ChlorophenyOnodomethyOdiphenvlsilane f5b!

A solution of 0.84 gram (2.4 mmoles) of (chloromethyl)(4- chlorophenyl)diphenylsilane and 1.10 grams (7.3 mmoles) of sodium iodide in 25 ml of anhydrous acetonitrile was heated at 82 °C for 48 hours. The mixture was cooled to room temperature, diluted with 109 excess ether, filtered and evaporated at reduced pressure. The remaining material was taken up in hexane and filtered. The solvent was removed at reduced pressure and the remaining solid was recrystallized from hexane to give 0.30 gram (0.69 mmole, 29%

yield) of (4-chlorophenyl)(iodomethyl)diphenylsilane ('5b'): mp 6 8 -

69 OC; lH NMR (CDCI 3 ) 7.35-7.59 (m, 14H, Si-Ar-H) , 2.70 (s, 2H, Si-

CH 2 -I); IR (KBr) 3067(w) , 2926(w) , 1577(w) , 1483(w) , 1427(m) ,

1381(w) , 1187(w) , 1113(m) , 1082(m) , 1014(w) , 997(w) , 813(w) ,

737(s) , 698(s) , 663(w) cnr*; MS M+ 433.9854 (Ci 9H i 6 ClISi, 2.15%)

, 293.0629 (C i 8 H i 4 ClSi, 100%). Anal. Calcd for C l 9 H i 6 ClISi: C, 52.49%; H, 3.71%. Found: C, 52.72%; H, 3.74% .

Preparation of (7odomethvn(4-methvlphenvOdiphenvlsilane (5d^

To 0.32 gram (1.0 mmole) of (chloromethyl)(4- methylphenyl)diphenylsilane in 10 ml of anhydrous acetonitrile was added 0.60 gram (4.0 mmoles) of sodium iodide. The homogeneous solution was then heated at 82 °C. Precipitation of sodium chloride was observed during the reaction, and heating was continued for 48 hours. The mixture was cooled to room temperature, diluted with excess ether, filtered and evaporated at reduced pressure. The residue was diluted with hexane and filtered from insoluble salts. After removal of solvent at reduced pressure, the residual oil was chromatographed on silica gel using 90% hexane-10% benzene as eluent. Isolation followed by recrystallization in hexane gave 0.20 gram (0.483 mmole, 49% yield) of (iodomethyl)(4- methylphenyl)diphenylsilane (5d): mp 75-76.5 °C; *H NMR (CDCI 3 ) 110 7.34-7.61 (m, 12H, Si-Ar-H) , 7.20-7.23 (d, 2H, H ortho to methyl) ,

2.7l(s, 2H, Si-CH 2 -I) , 2.38 (s, 3H, Si-Ar-CH3 ) ; IR (KBr) 3065(m) , 2927(w) ,1599(w) , 1487(w) , 1426(m) , 1393(w) ,1259(w) , 1191(w) , 1108(s) , 1028(w) , 997(w) , 803(m) , 739(s) , 710(m) , 697(s) ,

664(w) , 610(w); MS M+ 414.0295 (C 2 0 H l 9 lSi, 2.47%), 273.1180

( C i 9 H i 7 Si, 100%). Anal. Calcd for C 2 0 H l 9lSi: C, 57.97%; H, 4.62%.

Found C, 57.87%; H, 4.61%.

Preparation of flodomethvP^-methoxyphenvndiphenylsilane C5e)

To 0.82 gram (2.42 mmoles) of (chloromethyl)(4- methoxyphenyl)diphenylsilane in 25 ml of anhydrous acetonitrile was added 1.45 grams (9.7 mmoles) of sodium iodide. The homogeneous solution was then heated at 82 °C. Sodium chloride precipitated from the solution while heating was continued for 48 hours. The mixture was cooled to room temperature, diluted with ether, filtered and concentrated at reduced pressure. The remaining material was dissolved in hexane, filtered free of insolubles and concentrated at reduced pressure. Silica gel chromatography using 90% hexane-10% benzene as eluent, followed by isolation and recrystallization of the product from hexane, gave 0.41 gram (0.95 mmole, 39% yield) of (iodomethyl)(4-methoxyphenyl)diphenylsilane:

(5e) mp 59-61 oc; lH NMR (CDCI 3 ) 7.27-7.60 (m, 12H, Si-Ar-H) , 6.92-6.96 (d, 2H, H ortho to methoxy) , 3.83 (s, 3H, Si-Ar-CH^) ,

2.70(s, 2H, Si-CH 2 -I); IR (KBr) 3067(w) , 3021 (w) , 2928(w) , 2835(w) , 1654(w) , 1593(s) , 1563(w) , 1502(m) , 1457(w) , 111 1441(w) , 1427(m) , 1397(w) , 131 l(w) , 1280(s) , 1249(m) , 1183(m) , 111 3(s) , 1029(w) , 997(w) , 818(w) , 798(w) , 731(m) ,

699(s) , 667(w) , 616(w); MS M+ 430.0228 (C 2 0 H l 9 lOSi, 2.09%),

289.1068 (Ci 9 H i 7 0 Si, 71.63% major peak found). Anal. Calcd for

C2 0 H i 9lOSi: C, 55.82%; H, 4.45%. Found: C, 55.85%; 4.47%.

Preparation of (^-DimethvlaminophenvOnodomethyPdiphenvlsilane £ 5 0

To 0.40 gram (0.90 mmole) of (bromomethyl)(4- dimethylaminophenyl)diphenylsilane in 2 0 ml of anhydrous acetonitrile was added 2.0 grams (13 mmoles) of sodium iodide and the homogeneous solution was heated at 82 °C under argon. Sodium bromide precipitated from the reaction mixture and heating was continued for 18 hours. The mixture was cooled to room temperature, diluted with ether, filtered and concentrated at reduced pressure. The residue was diluted with hexane, filtered free of precipitated salts and concentrated at reduced pressure. Silica gel chromatography using 98% hexane-2% ethyl acetate as eluent followed by recrystallization of the product from hexane gave 0.25 gram (0.56 mmole, 55% yield) of (4-dimethylaminophenyl)(iodomethyl)diphenylsilane (50: mp 104-105.5 °C; NMR

(CDCI3 ) 7.33-7.62 (m, 12H, Si-Ar-H) > 6.72-6.75 (d, 2 H, H ortho to dimethylamino), 2.99 (s, 6 H, (CH 3 )2 N) , 2.70 (s, 2H, Si-CH 2 ~I); IR

(KBr) 3064(w) , 3049(w) , 3009(w) , 2922(w) , 2809(w) , 1594(s) , 1538(w) , 1515(m) , 1484(w) , 1441(w) , 1426(m) , 1363(m) , 112 1279(w) , 1228(w) , 1209(m) , 1112(s) , 1026(w) , 998(w) , 946(w) , 809(w) , 765(w) , 742(w) , 730(m) , 722(m) , 699(m) , 675(w) , 661(w) , 609(w) , 536(w) , 520(w) , 493(w) , 471(w) ; MS M+ 443.0598 (C2lH22lNSi, 53.00%) , 302.1424 (C20H20NSi, 88.19%

major peak found). Anal. Calcd for C 2 lH 2 2 lNSi: C, 56.89%; H, 5.02%.

Found: C, 56.75%; H, 5.03%.

Preparation of (Iodomethvl)triphenvlsilane (5c)

To 0.33 gram (1.07 mmoles) of (chloromethyl)triphenylsilane in 25 ml of anhydrous acetonitrile was added 0.64 gram (4.3 mmoles) of sodium iodide. The homogeneous solution was heated at 82 °C under argon. Sodium chloride precipitated from the reaction mixture, and heating was continued 48 hours. The mixture was cooled to room temperature, diluted with ether, filtered and concentrated at reduced pressure. The residue was diluted with hexane, filtered free of precipitated salts and the hexane was removed under vacuum. Chromatography on silica gel using 90% hexane- 10 % benzene as eluent followed by recrystallization from hexane gave 0.25 gram (0.64 mmole) of (iodomethyl)triphenylsilane

(5cl): mp 115-117 «C, lit.6 1 mp 117-119 <>C; lH NMR (CDCI 3 ) 2.73(s,

2H, SiCH 2 l) , 7.35-7.62 (m, 14H, aryl H); MS M+ 400.0150 (C l 9H l 7 lS i,

2.15%)., 259.0969 (Cl 8H i 5 Si, 100%). 113

REACTIONS OF ARYL(HALOMETHYL)DIPHENYLSILANES WITH FLUORIDE ION

The general conditions for reactions of aryl(bromomethyl)diphenylsilanes and aryl(iodomethyl)diphenylsilanes with tetrabutylammonium fluoride are as follows:

To a well stirred solution of 0.15 mmole of the silane in 0.2 ml of tetrahydrofuran at a specific temperature (23, 0 and -20 °C) was added dropwise over 2 minutes 0.35 ml (0.35 mmole) of 1M tetrabutylammonium fluoride in tetrahydrofuran. For the reactions at room temperature the solutions were stirred 18 hours. In experiments at lower temperatures the reaction mixtures were stirred for 30 minutes at the specific temperature and then placed in a refrigerator at 0 °C or a freezer at -20 °C for the duration of the reaction. Thin layer chromatography was used to determine when all of the starting material had been depleted. After the halosilane had reacted completely at the lower temperatures (10-15 days for 0 °C and 18-25 days for -20 °C) the reaction mixture was removed from the refrigerator or freezer and stirred at room temperature for 18 hours. The reaction mixtures were worked up by adding 2.5 ml of water and extracting four times with 0.30 ml of pentane. An internal standard, anisole, was added either at the beginning of a reaction or after work-up. The pentane fractions were combined and 114 analyzed on a capillary gas chromatograph. Typical results are as follows:

The products of reaction of (bromomethyl)(p - dimethylaminophenyl)diphenylsilane (0.0586 gram, 0.000148 mole) with 0.35 ml (0.35 mmole) of 1 M tetrabutylammonium fluoride at 23 °C were analyzed on the gas chromatograph under the following conditions: injector and detector port temperatures 225 °C, column temperature 60 for 1.40 minutes after which the temperature was increased 20 °C per minute until the column reached 140 °C. The analytical results are: ( 1) toluene (retention time 1 .0 0 minute, 0.086 mmole, 58%), (2) anisole (retention time 2.60 minutes, standard) and (3) p-dimethylaminotoluene (retention time 5.00 minutes, 0.0588 mmole, 40%).

The products from (iodomethyl)(/? - methoxyphenyl)diphenylsilane (0.0564 gram, 0.131 mmole) and 0.30 ml of 1 M tetrabutylammonium fluoride at 23 °C were analyzed gas chromatographically under the following conditions: injector and detector port temperatures 185 °C, column temperature 60 °C for 3.40 minutes, followed by an increase of 60 °C per minute until 100 °C. Analysis revealed: (1) toluene (retention time 1.00 minute, 0.0832 mmole, 63%), (2) anisole (retention time 3.28 minutes, standard), (3) p-methoxytoluene (retention time 4.5 minutes, 0.0448 mmole, 34%).

Gas chromatographic analysis (injector and detector port temperatures 185 °C, column temperature 60 °C for 3.4 minutes) of 115 the products of reaction of (iodomethy l)(p - methylphenyl)diphenylsilane (0.0644 gram, 0.000155 mole) with 0.36 ml (0.00036 mole) of 1 M tetrabutylammonium fluoride at 23 °C gave the following results: (1) toluene (retention time 1.00 minute, 0.101 mmole, 65%), (2) anisole (retention time 3.28 minutes, standard), and (3) p-methyltoluene (retention time 1.8 minutes, 0.0495 mmole, 32%).

The products from (bromomethyl)(p - chlorophenyl)diphenylsilane (0.0568 gram, 0.147 mmole) with 0.34 ml (0.34 mmole) of 1 M tetrabutylammonium fluoride at 0 °C as analyzed gas chromatographically (injector and detector port temperatures 185 °C, column temperature 60 °C for 4.00 minutes) are: (1) toluene (retention time 1.00 minute, 0.0737 mmole, 50%), (2) anisole (retention time 3.28 minutes, standard), and (3) p- chlorotoluene (retention time 3.65 minutes, 0.0718 mmole, 49%).

Analysis of the products from (bromomethyl)(p - trifluoromethylphenyl)diphenylsilane (0.0586 gram, 0.139 mmole) and 0.32 ml (0.00032 mole) of 1 M tetrabutylammonium fluoride at -20 °C (gas chromatograph: injector and detector port temperatures 185 °C, column temperature 60 °C for 3.5 minutes) gave the following results: ( 1) toluene (retention time 1 .0 0 minute, 0.0533 mmole, 38%), (2) anisole (retention time 3.28 minute, standard) and (3) p-trifluoromethyltoluene (retention time 1.15 minutes, 0.0804 mmole, 58%). 116

The products of reaction of bromomethyltriphenylsilane 0.815 gram, 0.204 mmole) with 0.47 ml (0.47 mmole) of 1 M tetrabutylammonium fluoride were analyzed on the gas chromatograph as follows: injector and detector port temperatures 185 °C, column temperature 60 °C for 3.5 minutes. Analysis gave the following results: (1) toluene (retention time 1.00 minute, 0.204 mmole, 100%) and (2) anisole (retention time 3.28 minutes, stan d a rd ).

REACTIONS OF ARYL(BROMOMETHYL)DIPHENYLSILANES WITH METHOXIDE ION

The general reaction conditions were as follows:

The silane, aryl(bromomethyl)diphenylsilane (0.00015 mole), was added to a large excess of sodium methoxide (generally 0 .1 1 gram, 0.0020 mole) in 0.40 ml of purified dioxane. The resulting mixture was vigorously stirred at room temperature for 2 days or until thin layer chromatography indicated no starting material remained. The mixture was then treated with 2.3 equivalents of tetrabutylammonium fluoride in tetrahydrofuran (commercially purchased as a 1M solution in tetrahydrofuran) and stirred at room temperature for 8 hours. The excess fluoride assured cleavage of the benzl groups from silicon because fluoride ion attacks silicon more efficiently than does methoxide. The mixture was worked up by adding 3 ml of water and extracting 4 times with 0.30 ml portions of 117 pentane. A known amount of the internal standard, anisole, was added to the combined pentane extracts and the solution was analyzed on a capillary gas chromatograph. Typical results are as follows:

The products of reactions of (bromomethyl)(p - dimethylaminophenyl)diphenylsilane (0.0689 gram, 0.174 mmole)

with 0.108 gram (0 .0 0 2 0 mole) of sodium methoxide were analyzed using conditions on the gas chromatograph as follows: injector and detector port temperatures 225 °C, column temperature 60 °C for 1.40 minutes increasing thereafter at a rate of 20 °C per minute until 140 °C. Analysis gave the following results: (1) toluene (retention time 1.00 minute, 0.109 mmole, 62%), (2) anisole (retention time 2.60 minutes, standard) and (3) p-dimethylaminotoluene (retention time 5.00 minutes, 0.0372 mmole 21.4%).

The products of reactions of (bromomethyl)(p - methoxyphenyl)diphenylsilane (0.0567 gram, 0.148 mmole) with

0 .1 2 2 gram (0.00226 mole) of sodium methoxide were analyzed using conditions on the gas chromatograph as follows: injector and detector port temperatures 185 °C, column temperature 60 °C for 3.40 minutes which were then increased 60 °C per minute until 100 °C. The analysis gave the following results: (1) toluene (retention time 1.00 minute, 0.0943 mmole, 64%), (2) anisole (retention time 3.28 minutes, standard), and (3) p-methoxytoluene (retention time 4.5 minutes, 0.0435 mmole, 29%) . 118

The products of reactions of (bromomethyl)(p - methylphenyl)diphenylsilane (0.0540 gram, 0.000147 mole) with 0.1161 gram (0.00215 mole) of sodium methoxide were analyzed on the gas chromatograph as follows: injector and detector port temperatures 185 °C, column temperature 60 °C for 3.40 minutes. The analysis gave the following results: (1) toluene (retention time 1.00 minute, 0.0895 mmole, 61%), (2) anisole (retention time 3.28 minutes, standard) and (3) p-methyltoluene (retention time 1.8 minutes, 0.0377 mmole, 26%) .

The products of reactions of (bromomethyl)(p- chlorophenyl)diphenylsilane (0.0667 gram, 0.172 mmole) with 0.0842 gram (0.00156 mole) of sodium methoxide were analyzed on the gas chromatograph as follows: injector and detector port temperatures 185 °C, column temperature 60 °C for 4.00 minutes. The analysis gave the following results: (1) toluene (retention time 1.00 minute, 0.886 mmole, 52%), (2) anisole (retention time 3.28 minutes, standard) and (3) p-chlorotoluene (retention time 3.65 minutes, 0.0723 mmole, 42%) .

The products of reactions of (bromomethyl)(p - trifluoromethylphenyl)diphenylsilane (0.0623 gram, 0.148 mmole) with 0.102 gram (0.00189 mole) of sodium methoxide were analyzed on the gas chromatograph as follows: injector and detector port temperatures 185 °C, column temperature 60 °C for 3.5 minutes. The analysis gave the following results: (1) toluene (retention time 1.00 minute, 0.0603 mmole, 41%), (2) anisole (retention time 3.28 119 minutes, standard) and (3) p-trifluoromethyltoluene (retention time 1.15 minutes, 0.0725 mmole, 49%).

The products of reaction of bromomethyltriphenylsilane (0.0838 gram, 0.235 mmole) with 0.0829 gram (1.5 mmole) of sodium methoxide were analyzed, on the gas chromatograph as follows: injector and detector port temperatures 185 °C, column temperature 60 °C for 3.5 minutes. The analysis gave the following results: (1) toluene (retention time 1.00 minute, 0.238 mmole, 101%) and (2) anisole (retention time 3.28 minutes, standard).

CALCULATION OF THE PRODUCT YIELDS

The product yields of the reactions were determined on the capillary gas chromatograph using an internal standard. Calibration curves for the products, toluene or substituted toluenes, versus the internal standard, anisole, were prepared and the slope of the line obtained determined the response factor of the products versus anisole. Authentic samples of the para-substituted-toluenes were commercially available except for p-trifluoromethyltoluene, which was prepared by the following method.

To 0.89 gram of magnesium in 20 ml of anhydrous ether was added dropwise 7.4 grams (0.033 mole) of 4-bromobenzotrifluoride in 15 ml of anhydrous ether. The resulting solution was refluxed for 1.5 hours and cooled to room temperature. The reaction medium was treated with 14.8 grams (0.104 mole) of methyl iodide in 25 ml of anhydrous ether and refluxed for 3 days. A 25 ml portion of 10% 120 sulfuric acid was added slowly and the ether layer was separated and the aqueous layer was extracted 3 times with 10 ml portions of ether. The organic layers were combined and washed with water, brine and dried over magnesium sulfate. The ether was filtered and removed at reduced pressure. Preparative gas chromatography gave 0.76 gram (0.00475 mole, 14%) 4-trifluoromethyltoluene. NMR

(CDCI3 , TMS -0.0003) 2.41 (2, 3H, Ar-CH3 ) , 7.2504-7.2851 (doublet 2H, H ortho to methyl) , 7.4847-7.5169 (doublet, 2H, H ortho to

trifluoromethyl). 35

Investigative Experiments

Reaction of fBromomethyOfp-dimethylaminophenvDdiphenvlsilane with Tetrabutylammonium Fluoride in Dioxane

To a stirred solution of 0.0581 gram (0.147 mmole) of (bromomethyl)(p-dimethylaminophenyl)diphenylsilane and 0.0135 gram of anisole in 0.2 ml of dioxane was added in 2 minutes 0.34 ml (0.34 mmole) of 1 M tetrabutylammonium fluoride in dioxane at 23 °C. The solution was stirred for 18 hours and worked-up by adding 2.5 ml of water and extracting 4 times with 0.30 ml of pentane. The pentane fractions were combined and analyzed gas chromatographically: injector and detector port temperatures 225 °C, column temperature 60 °C for 1.40 minutes after which the temperature was increased 20 °C per minute until the column reached 140 °C. The analytical results are: (1) toluene (retention time 1 .0 0 minute, 0.0886 mmole, 60%), ( 2 ) anisole (retention time 121 2.60 minutes, standard) and (3) p-dimethylaminotoluene (retention time 5.00 minutes, 0.0539 mmole, 37%).

Reaction of ('BromomethvPfp-dimethvlaminophenyPdiphenvlsilane with Sodium Methoxide in Tetrahydrofuran

To a solution of 0.0503 gram (0.127 mmole) of (bromomethyl)(p-dimethylaminophenyl)diphenylsilane in 0.40 ml of tetrahydrofuran was added 0.1100 gram (0.00204 mole) of sodium methoxide and the mixture was stirred for 48 hours. After thin layer chromatography indicated no starting material remained, 1.00 ml (0.001 mole) of 1 M tetrabutylammonium fluoride in tetrahydrofuran was added and the solution was stirred overnight. The reaction mixture was worked-up by adding 3 ml of water and extracting 4 times with 0.40 ml portions of pentane. The standard anisole, 0.0152 gram, was added and the solution was analyzed gas chromatographically to give: 1 () toluene (retention time 1 .0 0 minute,

0.0859 mmole, 6 8 %), (2) anisole (retention time 2.60 minutes, standard), and (3) p-dimethylaminotoluene (retention time 5.00 minutes, 0.029 mmole, 23%).

Reaction of (BromomethvPfp-dimethvlaminophenvPdiphenvlsilane with Tetrabutylammonium Fluoride in 96%Hexane- 4%Tetrahvdrofuran

(Bromomethyl)(p-dimethylaminophenyl)diphenylsilane (0.0517 gram, 0.1304 mmole) was added to 0.160 ml of 2.44 M tetrabutylammonium fluoride in tetrahydrofuran and 4 ml of hexane. Tetrabutylammonium fluoride was insoluble in the reaction medium. The solution was stirred for 2 weeks, and 0.0134 gram of 122 anisole was added. Gas chromatographic analysis gave: (1) toluene (retention time 1.00 minute, 0.0655 mmole, 50%), (2) anisole (retention time 2.60 minutes, standard), and (3) p - dimethylaminotoluene (retention time 5.00 minutes, 0.0543 mmole, 42%).

Reaction of fBromomethvDfp-dimethvlaminophenvDdiphenvlsilane with Tetrabutylammonium Fluoride in the Presence of Tri-n- b u tv la m in e

The silane, (bromomethyl)(p-dimethylaminophenyl)diphenylsilane (0.0520 gram, 0.131 mmole), was added to a solution of 0.0862 gram (0.465 mmole) of tri-n-butylamine, 0.0158 gram of anisole, 0.39 ml (0.39 mmole) of 1 M tetrabutylammonium fluoride in tetrahydrofuran and 0.62 ml of tetrahydrofuran. After the reactants had been stirred for 18 hours, gas chromatographic analysis gave: (1) toluene (retention time 1.00 minute, 0.0788 mmole, 60%), ( 2 ) anisole (retention time 2.60 minutes, standard), and (3) p-dimethylaminotoluene (retention time 5.00 minutes, 0.0539 mmole, 41%).

Reaction of ('BromomethvDCp-dimethvlaminophenvlldiphenvlsilane with Tetrabutylammonium Fluoride in the Presence of Sodium M ethoxide

The silane, (bromomethyl)(p-dimethylaminophenyl)diphenylsilane (0.0508 gram, 0.128 mmole), was added to a mixture of 0.111 gram of sodium methoxide (0.00205 mole), 0.40 ml (0.40 mmole) of 123 1 M tetrabutylammonium fluoride in dioxane and 0.50 ml of dioxane. The mixture was stirred 20 hours and worked up by adding 0.0171 gram of anisole and 3 ml of water and extracting 4 times with 0.40 ml portions of pentane. The combined pentane fractions were analyzed gas chromatographically to give: (1) toluene (retention time 1.00 minute, 0.0762 mmole, 59%), (2) anisole (retention time 2.60 minutes, standard), and (3) p-dimethylaminotoluene (retention time 5.00 minutes, 0.0452 mmole, 35%).

Reaction of (BromomethvlKp-dimethylaminophenvUdiphenvlsilane with Cesium Fluoride

A mixture of 0.1841 gram of cesium fluoride in 1 ml of tetrahydrofuran was treated with 0.0507 gram (0.128 mmole) of (bromomethyl)(p-dimethylaminophenyl)diphenylsilane and stirred for 60 hours. After thin layer chromatography indicated that no starting material remained, the mixture was treated with 0.39 ml of 1 M tetrabutylammonium fluoride in tetrahydrofuran and stirred for 1 day. Upon addition of 0.0151 gram of anisole the mixture was worked-up by adding 3 ml of water and extracting 4 times with 0.40 ml of pentane. The combined pentane fractions were analyzed gas chromatographically to give: 1) toluene (retention time 1 .0 0 minute, 0.0651 mmole, 51%), (2) anisole (retention time 2.60 minutes, standard), and (3) p-dimethylaminotoluene (retention time 5.00 minutes, 0.0532 mmole, 42%). 124 Reactions of (BromomethvlVp-dimethvlaminophenvDdiphenylsilane with Fluoride Ion in Varied Concentrations

These experiments were all conducted essentially identically in that only the amount of solvent used was varied. The silane, generally 0.0525 gram (0.132 mmole) of (bromomethyl)(p- dimethylaminophenyl)diphenylsilane was added to a solution of 3 equivalents of tetrabutylammonium fluoride in varied amounts of tetrahydrofuran (the amounts of solvent used varied from 0.16 ml to 100.4 ml). The solution was stirred for 18 hours and then worked- up after adding a known amount of anisole as standard. The reaction products were analyzed gas chromatographically and the yields determined as described in previous examples. In cases when large amounts of solvents were used, the reaction solutions were analyzed directly .

Preparation of Racemic (Methoxv^methvKl-naphthyDphenvlsilane (1051

To a stirred mixture of 75.04 grams (3.09 moles) of magnesium in 300 ml of benzene, 200 ml of ether and 100 ml of tetrahydrofuran was added 608.7 grams (2.94 moles) of 1-bromonaphthalene over 2 hours. The solution warmed as a result of formation of the Grignard reagent. After the stirred solution had been heated at 55 °C for an additional 60 minutes, 520.8 grams (2.86 moles) of dimethoxymethylphenylsilane (104) was added in 5 minutes. The mixture was heated at 55 °C for 12 hours, cooled to room 125 temperature, treated with saturated ammonium chloride solution, washed with water and brine, dried over sodium sulfate and filtered. The reaction mixture was fractionally distilled to give (methoxy)methyl(l-naphthyl)phenylsilane (1051. bp 154-160 °C, 0.30 torr. The product was recrystallized from hexane to give 484.9 grams (1.74 moles, 59% yield) of 105 as a white solid: mp 61-63 °C, lit.56 mp 62.5-63.5 »C; lH NMR (CDCI 3 ) 0.79 (s, 3H, Si-CH 3 ) , 3.57 (s,

3H, Si-OCH3 ) , 7.28-8.18 (m, 12H, aryl H).

Preparation of (-l-IY-lMenthoxylmethvKl-naphthvllphenvlsilanes OM)

To 305 ml of dry toluene was added 484.9 grams (1.74 moles) of l-(methoxy)methyl(l-naphthyl)phenylsilane (1051. 136.0 grams (0.87 mole) of (1R, 2S, 5R)-(-)-menthol, and 0.2 gram of potassium hydroxide. The solution was heated to 135-150 °C for 4 hours while removing the by-product methanol through a fractionating column (40 cm x 1 cm) packed with stainless steel staples. The pot was cooled to room temperature and the contents passed through a bed of silica gel. The solution was fractionally distilled to give a sirupy diastereomeric mixture of crude menthoxysilanes with a boiling point at 189-195 °C at 0.10 torr. The sirupy mixture was dissolved in twice its volume of pentane and stored overnight at -78 °C. The solid which crystallized was filtered and recrystallized twice from pentane to give 110 grams (0.27 mole) of (-)-[(-)- menthoxy]methyl(l-naphthyl)phenylsilane (1071 crystals: mp 81-83 OC, lit.56 mp 82-84 <>C. 126

Preparation of f+WMethyPd-naphthyPphenvlsilane (108^

To a mixture of 10 grams of lithium aluminum hydride in 110 ml of dry ethyl ether at 0 °G was added 84.70 grams (0.21 mole) of (-)-[(-)menthoxy]methyl(l-naphthyl)phenylsilane (1071 in 110 ml of dry di-n-butyl ether. The diethyl ether was distilled from the solution and the mixture was heated at 80 °C overnight. Excess lithium aluminum hydride was decomposed with acetone, and the mixture was poured over ice and treated with concentrated hydrochloric acid. The organic layer was separated, washed with water and brine, dried over sodium sulfate and filtered. The solvent was removed via distillation, and the (-)-menthol by-product was removed by vacuum distillation at 0.05 torr until a head temperature of 125 °C and pot temperature of 175 °C were reached. Two recrystallizations of the remaining oil from hexane gave 43.44 grams (0.175 mole, 84% yield) of 108. [a]23D +32.8°, (0.1050 gram in

2 ml cyclohexane), [lit .56 [a]23D +33.4°, 98% optical purity]; mp 61-63

°C, lit.56 mp 61.5-63 <>C; 1r NMR (CDCI3 ) 0.75-0.77 (d, 3H, Si-CH 3 ) , 5.33-5.37 (q, 1H, Si-H) , 7.34-7.93 (m, 12H, aryl H).

Preparation of (+WDibromomethvl'lmethvl(l-naphthvl,)phenvlsilane 0-0.9)

Into a flame dried round bottom flask under argon was added 8.36 grams (0.0336 mole) of (+)-methyl(l-naphthyl)phenylsilane (10 81. 17.6 grams (0.0333 mole) of phenylmercuric- 127 tribromomethane and 150 ml of dry benzene. The solution was refluxed for 4 hours. After cooling, the solution was filtered free of the precipitate of phenymercuric bromide, followed by removal of benzene at reduced pressure. The remaining material was taken up in pentane and the insolubles were filtered. The pentane was removed at reduced pressure and the remaining material was chromatographed on silica gel using 90% hexane-10% benzene as eluent. The product 109 was obtained as a light brown oil (7.14 grams, 0.017 mole, 51% yield) that did not crystallized using

standard techniques^ 1h NMR (CDCI 3 ) 1.06 (s, 3H, Si-CH 3 ) , 5.85 (s,

1H, Si-CHBr2 ) , 7.33-7.97 (m, 12H, aryl H).

Preparation of f+WBromomethyllmethvKT-naphthvllphenvlsilane m

A solution of 5.5 ml (2.5 M, 0.014 mole) of n-butyllithium in hexane was added dropwise in 5 minutes to 5.5 grams (0.013 mole) of (+)-(dibromomethyl)methyl(l-naphthyl)phenylsilane (1091 in 400 ml of dry ether at -78 °C under argon. The deep brown solution was stirred for 10 minutes at -78 °C, treated with hydrogen bromide, warmed to room temperature and then 300 ml of water was added. The organic layer was separated, washed with water and brine, dried over sodium sulfate and filtered. Removal of solvent at reduced pressure gave an oil that was chromatographed on silica gel using 90% hexane-10% benzene as eluent. Isolation and recrystallization from hexane gave 3.00 grams (0.0079 mole, 67% yield) of (+)- 128

(bromomethyl)methyl(l-naphthyl)phenylsilane (&): mp 62-63.5 °C, lit.58 mp 63.5-64.5 °C; optical rotation [a]23D +8.29° (0.0135 gram in

1 ml of cyclohexane), lit. [o c]23d +9.15°; JH NMR (CDCI3 ) 0.90 (s, 3H,

Si-C H 3 ) , 3.11 (s, 2H, Si-C&Z-Br) , 7.32-7.96 (m, 12H, aryl H). MS M+

340.0247 (Ci 8H i 7 BrSi, 16.17%) , 342.0188 (Ci 8H i 7 BrSi, 18.63%) , 247.0208 (CnH isSi, 100%).

Reaction of (+)-(Bromomethvl)methvl(l-naphthvl)phenvlsilane (81 with Sodium Methoxide

To a 10 ml round bottom flask equipped with a stir bar under argon was added 0.90 gram (0.00264 mole) of (+)-(bromomethyl)(l- naphthyl)phenylmethylsilane (&, [a ]23D +8.29°), 0.25 gram of sodium methoxide (0.046 mole) and 16 ml of dry dioxane. The contents were stirred for 2 hours using thin layer chromatography to follow the reaction (formation of 1-methylnaphthalene was observed via thin layer chromatography). The reaction mixture was diluted with a large excess of hexane and the resulting mixture was filtered. The solvent was removed at reduced pressure and the remaining oil was chromatographed on silica gel. An eluent solvent system of 85% hexane/15% benzene was used to elute unreacted starting material led to recovery of 0.39 gram (0.00114 mole, 43% recovered) of £., [

(+)-benzyl(methoxy)methyl(l-naphthyl)silane ( 1 1 0 1 . was isolated along with (methoxy)methyl(l-naphthylmethyl)phenylsilane ( 1 1 1 ) 129 in a 10.5/1 ratio (110/1 111 upon 1H NMR analysis. After further separation on silica gel, 0.112 gram (0.397 mmole, 15% yield) of the product of phenyl migration .110. was isolated, [a] 23D +39.5° (0.112 gram in 5 ml of cyclohexane); *H NMR (CDCl3;7.2605, CHCI 3 ) 0.47 (s,

3H, Si-CH3 ) , 2.51-2.66 (q, 2H, Si-CH 2 -Ph) , 3.45 (s, 3H, Si-OCH3 ) , 6.95-8.29 (m, 12H, aryl H) ; IR (neat) 3057(m) , 3025(m) , 2999(m) , 2957(m) , 2933(m) , 2898(m) , 2830(m) , 1940(w) , 1885(w) , 1810(w) , 1747(w) , 1599(m) , 1566(m) , 1504(s) , 1493(s) , 1452(s) , 1427(m) , 1403(m) , 1320(m) , 1254(s) , 1206(s) , 1186(s) , 1146(s) , 1080(s) , 1024(m) , 984(s) , 952(m) , 904(m) , 827(w) , 798(s) , 779(s) , 751(s) , 698(w) , 670(m) , 633(m) , 583(w) , 563(m) ,

531(m) , 517(m) , 480(w) ; MS M+ 292.1257 (Ci 9H 2 0 OSi, 8.69%) , 201.0741 (Cl2Hi30Si, 100%).

Preparation of Racemic BenzyKmethoxvlmethvlfl-naphthvllsilane (LI 4)

Benzylmagnesium chloride was prepared by adding dropwise 6.33 grams (0.05 mole) of benzyl chloride to 1.28 grams (0.055 mole) of magnesium in 12 ml of ether. The Grignard reagent was transfered to a solution of 16.33 grams (0.07 mole) of (dimethoxy)methyl(l-naphthyl)silane (1131 in 25 ml of dry ether. The reaction mixture was refluxed for 5 hours, cooled and filtered. Fractional vacuum distillation was used to isolate 9.0 grams (0.031 mole, 62% yield) of benzyl(methoxy)methyl(l-naphthyl)silane (1141 as an oil: bp 149-154 <>c 0.05 torr ; lH NMR (CDCI 3 , TMS 0.0582)

0.52 (s, 3H, Si-CH 3 ) , 2.55-2.71 (q, 2H, Si-CH2 -Ph) , 3.49 (s, 3H, Si- 130 OCH3) , 7.00-8.36 (m, 12H, aryl H) ; IR (neat) 3057(s) , 3024(s) ,

2999(m) , 2957(s) , 2933(s) , 2897(m) , 2830(s) , 1942(w) , 1884(w) , 1810(w) , 1747(w) , 1599(s) , 1566(m) , 1504(s) , 1493(s) , 1452(s) , 1427(m) , 1404(m) , 1319(m) , 1254(s) , 1206(s) , 1186(s) , 1146(s) , 1082(s) , 1024(m) , 984(s) , 952(m) , 904(m) , 827(w) , 798(w) , 779(w) , 751(w) , 699(s) , 670(m) , 633(m) , 583(w) , 563(m) ,

531(m) , 517(m) , 480(s); MS M+ 292.1276 (Ci 9H 2 0 OSi, 7.94%) ,

201.0756 (Ci 2 H i 3 0 Si, 100%). Anal. Calcd for Ci9H20OSi: 78.03%; H,

6.89% : Found C, 78.16%; H, 6.90%.

Preparation of DimethoxymethvlCl-naphthvnsilane (113)

To 4.90 grams (0.20 mole) of magnesium in 20 ml benzene, 10 ml of tetrahydrofuran and 30 ml of ether was added over 30 minutes 38.1 grams (0.184 mole) of 1-bromomethylnaphthalene in 20 ml of ether. The mixture was refluxed for 30 minutes and transferred to 75.1 grams (0.55 mole) of methyltrimethoxysilane (112.) in 80 ml of ether. The solution was stirred for 2 hours and filtered. The product, dimethoxymethyl(l-naphthyl)si1ane (113} (27.65 grams, 0.12 mole), was collected by vacuum distillation at 110 °C - 113 oc at 0.10 torr; *H NMR (CDC13, TMS 0.0686) 0.55 (s, 3H, Si-

CH 3 ) , 3.67 (s, 6 H, Si-OCH3 ) , 7.50-8.38 (s, 7H, aryl H). amPreparation of fMethoxylmethvin-naphthylmethyDphenvlsilane 131

To a mixture of 1.28 grams (0.53 mole) of magnesium in 12.5 ml of dry ether was added dropwise 8.83 grams (0.05 mole) of 1- chloromethylnaphthalene in 10 ml of ether and 25 ml of benzene. The mixture was stirred for 1 hour and then transferred dropwise to 9.12 grams (0.05 mole) of (dimethoxy)methylphenylsilane (104) in 25 ml of dry ether. The resulting mixture was heated at 55 °C for 3 hours, cooled, filtered and fractionally distilled to give 4.1 grams (0.014 mole, 28% yield) of (methoxy)methylphenyl(l- naphthylmethyl)silane (111): bp 145-149 °C 0.05 torr; lH NMR

(CDCI3 ; TMS 0.0653), 0.29 (s, 3H, Si-CH 3) , 2.83-3.03 (q, 2H, Si-CH2 - 1-Np) , 3.44 (s, 3H, Si-0CH3) 7.21-8.01 (m, 12H, aryl H) ; IR neat 3065(m) , 3044(m) , 2957(m) , 2898(w) , 283l(m) , 1592(m) , 1576(w) , 1509(w) , 1461(w) , 1427(m) , 1394(m) , 1347(w) , 1254(m) , 1173(m) , 1154(m) , 1116(s) , 1085(s) , 1009(m) , 998(w) , 870(m) , 793(s) , 774(s) , 738(s) , 699(s) , 646(w) , 623(w) , 583(w) ,

541(w) , 472(m) ; MS M+ 292.1259 (13.13%, C i 9H 2 0 OSi) , 151.0605

(100%, C8HnOSi). Anal. Calcd for Ci 9H 2 0 OSi: 78.03%; H, 6.89%. Found C, 78.04%; H, 6.93%.

Reaction of (+)-Benzvl(methoxy)methvl(l-naphthvl)silane (110) with Phenvllithium

Optically active (+)(methoxy)methyl(l-naphthyl)benzylsilane (110. 0.0580 gram, 0.198 mmole) was dissolved in 4 ml of ether and treated with 0.13 ml of phenyllithium (1.8M in ether/cyclohexane, 0.234 mmole) and stirred for 2 hours, diluted with hexane and 132 filtered. After removal of solvent at reduced pressure the remaining material was chromatographed on silica gel using 90% hexane/10% benzene to yield 0.0606 gram (0.179 mmole, 90% yield) of (-)- benzylmethyl(l-naphthyl)phenylsilane (1161. [a]23D -5.25° (0.0606 gram in 1 ml of cyclohexane); lH NMR (CDCI 3 ) 0.58 (s, 3H, Si-CKh) ,

2.77-2.90 (q, 2H, Si-CH 2 -Ph) , 6.80-7.93 (m, 17H, aryl H) ; IR neat 3052(m) , 3024(m) , 2958(w) , 2928(w) , 2896(w) , 2302(w) , 1952(w) , 1884(w) , 1812(w) , 1718(w) , 1654(w) , 1599(m) , 1565(m) , 1505(m) , 1493(s) , 1451(m) , 1427(s) , 1409(m) , 1318(m) , 1264(s) , 1252(s) , 1218(m) , 1205(s) , 1156(m) , 1145(m) , 1107(s) , 1058(m) , 1024(m) , 998(m) , 981(m) , 950(w) , 904(w) , 827(s) ,

797(s) , 777(s) , 736(s) , 699(s) , 668 (m) , 639(m) , 582(w) , 564(w) , 530(w) , 517(m) , 484(s) , 470(m) ; MS M+ 338.1498 (6.23%,

C2 4 H 2 2 SO , 247.0974 (100%, C n H is S i) .

Reaction of Racemic Benzvlfmethoxylmethvin-naphthvllsilane with Phenvllithium

Racemic benzyl(methoxy)methyl(l-naphthyl)silane (114. 1.52 gram, 0.0052 mole), in 10 ml of ether was added to a solution of 0.0052 mole of phenyllithium in ether [prepared by adding 0.82 gram (0.0052 mole) of bromobenzene to 0.0742 gram (0.0107 mole) of lithium in 10 ml of ether] and the mixture was then stirred overnight. The solution was diluted with hexane and filtered. The solvent was removed at reduced pressure and the remaining oil was 133 chromatographed on silica gel using 90% hexane/10% benzene eluent to isolate 1.02 grams (0.0030 mole, 58% yield) of racemic

benzylmethyl(l-naphthyl)phenylsilane (115. 116V. NMR (CDCI 3 )

0.58 (s, 3H, Si-Ctt3 ) , 2.77-2.90 (q, 2H, Si-CH 2 -Ph) , 6.81-7.89 (m,

17H, aryl H) ; IR neat 3054(m) , 3022(m) , 2959(w) , 2894(w) , 2302(w) , 1948(w) , 812(w) , 1654(w) , 1599(m) , 1504(m) , 1492(s) , 1451(m) , 1427(s) , 1407(m) , 1318(m) , 1252(s) , 1205(s) , 1145(m) , 1107(s) , 1057(m) , 1024(m) , 998(m) , 981(m) , 949(w) ,

904(w) , 826(s) , 796(s) , 777(s) , 732(m) , 698(s) , 668 (m) \ 639(m) , 563(w) , 530(m) , 517(s) , 483(m). MS M+ 338.1497 (6.52%, C24H22Si) , 247.0942 (100%, CnH isSi). Anal. Calcd for C24H22Si: C, 85.13%, H, 6.55%. Found C, 85.17%, H, 6.55%.

Reaction of (+l(Bromomethvllmethvl(l-naphthvPphenvlsilane (81 with Phenvlmagnesium Bromide

Phenylmagnesium bromide, (0.00179 mole) in tetrahydrofuran, was added to 0.55 gram (0.0016 mole) of (+)-

(bromomethyl)methyl(l-naphthyl)phenylsilane ( 8_) in 4 ml of tetrahydrofuran containing a small amount of copper iodide. The resulting mixture was refluxed 6 hours while being monitored by thin layer chromatography. The solution was cooled and the solvent removed at reduced pressure. The remaining material was chromatographed on silica gel using 90% hexane-10% benzene as eluent to give 0.4518 gram (0.00133 mole, 83% yield) of (+)- benzylmethyl(l-naphthyl)phenylsilane (1151. [a]23D +6.15° (0.3497 134 gram in 5 ml cyclohexane) : NMR (CDCI 3 ) 0.59 (s, 3H, Si-CH3 ) ,

2.79-2.91 (q, 2H, Si-CH2 -Ph) , 6.82-7.90 (m, 17H, aryl H) ; IR neat

3054(m) , 3023(m) , 2959(w) , 2928(w) , 2895(w) , 2362(w) , 2302(w) , 1812(w) , 1654(w) , 1599(m) , 1504(m) , 1492(s) , 1451(m) , 1427(s) , 1408(m) , 1318(m) , 1251(s) , 1218(w) ,1205(s) , 1156(m) ,1145(m) , 1107(s) , 1058(m) , 1024(m) , 998(m) , 981(m) ,

950(w) , 904(w) , 827(s) , 796(s) , 777(s) , 735(m) , 699(s) , 668 (m) , 639(m) , 619(w) , 564(w) , 531(m) , 517(s) , 483(m) , 470(m) ; MS M+

338.1492 (5.71%, C 2 4 H 2 2 SO , 247.0993 (100%, C nH isSi).

Reaction of ('+l(BromomethvPmethvKT-naphthvPphenvlsilane (81 with Sodium Ethoxide

Sodium ethoxide was prepared by adding 0.0608 gram (0.00264 mole) of sodium to 10 ml of anhydrous ethanol. After depletion of the sodium, ethanol was removed under high vacuum overnight. The contents were placed under argon and 10 ml of dry dioxane and 0.65 gram (0.0019 mole) of (+)(bromomethyl)methyl-(l- naphthyl)phenylsilane (SO were added. The mixture was stirred for 4 hours using thin layer chromatography to monitor the reaction. The mixture was diluted with hexane, filtered and concentrated at reduced pressure. The remaining oil, on chromatography on silica gel using 90% hexane-10% benzene eluent, yielded 0.3182 gram (0.9323 mmole, 49% recovered) of unreacted starting material (80. The eluent was changed to 97% hexane-3 % ethyl acetate to elute 0.0571 gram (0.186 mmole, 9.8% yield) of (+)-benzyl(ethoxy)methyl(l- 135 naphthyl)silane (IIS'). [a]23D 3 9.4°, (0.0571 gram in 3 ml of

cylclohexane); lH NMR (CDCI 3 , TMS 0.0017) 0.46 (s, 3H, Si-CH 3 ) ,

1.14-1.20 (t, 3H, Si-OCH2 CH3 ) , 2.52-2.64 (q, 2H, Si-CH 2 Ph) , 3.66-

3.69 (q, 2H, Si-OCH_2 CH 3 ) , 6.93-8.34 (m, 12H, aryl H) ; IR neat 3058(m) , 2972(s) , 2890(m) , 2360(w) , 1941(w) , 1600(m) , 1505(m) , 1493(s) , 1451(m) , 1427(m) , 1390(m) , 1319(m) , 1253(s) , 1206(m) , 1158(s) , 1100(s) , 1076(s) , 1024(m) , 984(m) , 946(s) ,

827(s) , 797(s) , 778(s) , 698(s) , 668 (m) , 637(m) , 564(w) , 531(w) ,

517(w) , 480(m) ; MS M+ 306.1434 (C 2 0 H 2 2 OSi, 14.38%) , 215.0856 (Cl3Hi50Si, 100%).

Preparation of Racemic Benzvlethoxy(methyl)(l-naphthvl)silane (1 1 9 )

To 3 ml of ethanol in 20 ml of toluene was added 0.62 gram

(0.0021 mole) of benzyl(methoxy)methyl(l-naphthyl)silane (114) and a catalytic amount of potassium hydroxide. The solution was heated at 80 °C for 4 hours, cooled to room temperature, filtered and the solvent was removed by distillation. Chromatography of the remaining oil on silica gel using 98% hexane-2% ethyl acetate as eluent gave 0.30 gram (0.98 mmole, 46% yield) of ethoxy(methyl)(l- naphthyl)benzylsilane (119): lH NMR (CDCI 3 , TMS 0.0011) 0.47 (s,

3H, Si-CH 3 ) , 1.15-1.21 (t, 3H, Si-OCH2 CH 3 ) , 2.51-2.66 (q, 2H, Si-

CH 2 Ph) , 3.67-3.70 (q, 2H, Si-OCH 2 CH 3) , 6.93-8.35 (m, 12H, aryl H) ;

IR neat 3079(w) , 3057(m) , 2971(s) , 2892(m) , 2360(w) , 1941(w) , 1600(m) ,1565(w) , 1505(m) , 1493(s) , 1451(m) , 1427(m) , 1390(m) , 1319(m) ,1291(w) , 1254(s) , 1206(m) , 1161(s) ,1146(s) , 136 1102(s) , 1078(s) , 1024(m) , 1001(w) , 984(m) , 947(s) , 903(w) , 828(s) , 798(s) , 780(s) , 752(m) , 698(s) , 670(m) , 636(m) , 564(w) ,

531(w) , 517(w) , 480(m) ; MS M+ 306.1453 (C 2 0 H 2 2 OSi, 10.35%) ,

215.0908 (Ci3H i 5 0 Si, 100%). Anal Calcd for C 2 0 H 2 2 OSi, 78.12%; H, 7.54%: Found C, 78.31%; H, 7.29%.

Reaction of (+)-Benzvlfethoxv')methvin-naphthyllsi1ane (1181 with Phenvllithium

Optically active (+)-benzyl(ethoxy)methyl(l-naphthyl)silane (1 18. 0.055 gram, 0.18 mmole), was dissolved in 5 ml of dry ether an treated with 0.11 ml (1.8 M in ether/ cyclohexane, 0.20 mmole) of phenyllithium. The mixture was monitored by thin layer chromatography while being stirred for 6 hours. The solvent was removed at reduced pressure and the crude product was chromatographed on silica gel using 90% hexane-10% benzene as eluent to give 0.0521 gram (0.159 mmole, 85% yield) of (-)- benzylmethyl(l-naphthyl)phenylsilane (116V [a]23D -5.5°, (0.040 gram in 1 ml of cyclohexane); *H NMR (CDCI 3 ) 0.58 (s, 3H, Si-CHA) ,

2.77-2.90 (q, 2H, Si-CH 2 -Ph) , 6.80-7.93 (m, 17H, aryl H).

Reaction of f+lfBromomethvllmethvlfl-naphthvDphenvlsilane (S') with Sodium Isopronoxide

Sodium isopropoxide was prepared by adding 0.0645 gram (0.00281 mole) of sodium to 2 ml of isopropyl alcohol. After depletion of the sodium, excess alcohol was removed at reduced pressure. The contents was placed under argon and combined with 15 ml of dry dioxane and 0.65 gram (0.0019 mole) of (+)- 137 (bromomethyl)methyl(l-naphthyl)phenylsilane (&) was added. After 3 hours of stirring the mixture was diluted with 100 ml of hexane, filtered, and concentrated at reduced pressure. The remaining oil was chromatographed on silica gel using 90% hexane- 10% benzene as eluent to give &, (0.36 gram, 0.00105 mole, 55% recovered). Use of 98% hexane-2% ethyl acetate as eluent yielded 0.031 gram (0.0967 mmole, 5.1%) of ( + )- benzyl(isopropoxy)methyl(l-naphthyl)silane (1201. [a]23D 28.1°,

(0.031 gram in 2 ml of cyclohexane); NMR (CDCI 3 ) 0.49 (s, 3H, Si-

CH 3 ) , 1.10-1.17 (q, 6 H, Si-CH(CH3 )2 ) , 2.51-2.64 (q, 2H, Si-CH2 Ph) ,

3.9-4.1 (septet, 1H, Si-CH(CH3)2 ) , 6.90-8.41 (m, 12H, aryl H).

Preparation of Racemic (Tsopropoxvlmethvin-naphthvOphenvlsilane 121)

To 0.62 gram (0.00212 mole) of benzyl(methoxy)methyl(l- naphthyl)silane (114.) in 25 ml of dry toluene was added 6 ml of isopropyl alcohol and a catalytic amount of potassium hydroxide. The solution was heated to 80 °C and stirred for 2 days. Thin layer chromatography gave evidence for 121 by comparison with 1 2 0 . Chromatography using 97% hexane-3 % ethyl acetate yielded 0.10. gram (0.31 mmole, 15%) of (isopropoxy)methyl(l- naphthyl)phenylsilane (121); lH NMR (CDCI 3 ) 0.49 (s, 3H, SiCH3 ,

1.11-1.17 (q, 6 H, Si-CH(CH 3 )2 ) , 2.52-2.64 (q, 2H, Si-CH2 Ph) , 4.00-

4.08 (septet, 1H, Si-CH(CH 3 )2 ) , 6.91-8.40 (m, 12H, aryl H).

Reaction of (+')('Isopropoxvlmethvin-naphthvl')benzvlsilane (1211 with Phenvllithium 138

Optically active ( + )-(isopropoxy)methyl( 1 - naphthyl)benzylsilane (121. 0.031 gram, 0,0967 mmole), was dissolved in 5 ml of ether and treated with 0.06 ml (1.8M in ether/cyclohexane, 0.108 mmole) of phenyllithium. After being

stirred for 2 hours the solution was diluted with hexane, filtered and the solvent was removed at reduced pressure. The remaining oil was chromatographed on silica gel using 90% hexane/10% benzene as eluent to isolate 0.0294 gram (0.0868 mmole, 90%) of (-)- benzylmethyl(l-naphthyl)phenylsilane (116). [a]23D -5.57°, (0.0294 gram in 1 ml of cyclohexane); lH NMR (CDCI 3) 0.58 (s, 3H, Si-CH3 ) ,

2.77-2.90 (q, 2H, Si-CH 2 -Ph) , 6.80-7.93 (m, 17H, aryl H).

Reaction of (+l-(Bromomethvllmethv1(l-napthyllphenvlsilane (81 with Sodium Methoxide at 0 °C

Silane (0.45 grams, 0.0013 mole) was treated with 0.1530 gram (0.0028 mole) of sodium methoxide in 16 ml of dioxane/tetrahydrofuran (88/12) at 0 °C with stirring for 6 hours. The solution was diluted in hexane and, filtered and the solvent was removed at reduced pressure. The remaining material was chromatographed on silica gel using 90% hexane/10% benzene to elute unreacted 8., followed by 97% hexane/3% ethyl acetate eluent to give 0.128 gram (0.44 mmol, 34% yield) of (+)- benzyl(methoxy)methyl(l-naphthyl)silane (1101: [a]23D +38.82°.

Reaction of (+l(Bromomethvllmethvl(l-naphthvllphenvlsilane (81 with Cesium Fluoride Followed by Phenvllithium 139

Silane £. (0.1122 gram, 0.3287 mmole) was added to 0.2208 gram (0.00151 mole) of cesium fluoride in 4 ml of dry ft tetrahydrofuran. The mixture was stirred at room temperature for 24 hours. The solution was diluted with hexane, filtered and the solvent removed at reduced pressure. The residue was dissolved in 4 ml of ether, treated with 0.30 ml of phenyllithium (1.8 M, 0.54 mmole) and stirred overnight. The solution was diluted with hexane, filtered and the solvent removed at reduced pressure. The remaining oil, upon chromatography on silica gel using 90% hexane- 10% benzene eluent, gave 0.031 gram (0.0916 mmole, 28% yield) benzyl(methyl)(l-naphthyl)phenylsilane ('130'). Optical rotational measurements of 130 in cyclohexane indicated no optical activity.

lH NMR (CDCI3 ) 0.58 (s, 3H, Si-CH3 ) , 2.77-2.89 (q, 2H, Si-CH 2 -Ph) , 6.78-7.92 (m, 17H, aryl H).

Reaction of (+'X'Bromomethvnmethvl(l-naphthvl>>phenvlsilane (81 with Cesium Fluoride

Silane &, (+)(bromomethyl)methyl(l-naphthyl)phenylsilane (0.112 gram, 0.328 mmole), was added to 0.228 gram (0.0015 mole) of cesium fluoride in 4 ml of dry tetrahydrofuran. The mixture was stirred overnight at room temperature and diluted with 50 ml of hexane. The solution was filtered free of cesium fluoride and the solvent was removed at reduced pressure. The remaining material was chromatographed on 5 grams of silica gel using 75% hexane-25% benzene as the eluent. Isolation gave 0.034 gram (0.1213 mmole, 140 37%) of benzyl(fluoro)methyl(l-naphthyl)silane ( 1 291. The product

.129. had no optical activity in cyclohexane; NMR (CDCI 3 ) 0.5712-

0.6015 (d, 3H, Si-CH 3 ) , 2.55-2.74 (octet, 2H, Si-CH 2 Ph) , 7.00-8.05 (m, 12H, aryl H); MS M+ 280.1051 (36.82%, C isH nFSi) , 189.0596 (100%, CnHioFSi).

Preparation of Benzvlffluorolmethvlfl-naphthvllsilane (1291

To a flame dried round bottom flask under argon was added 0.75 gram (0.00256 mole) of racemic benzyl(methoxy)methyl(l- naphthyl)silane 114. 10 ml of ether, and 0.5 ml of boron trifluoride ethereate. The mixture was stirred for 4 hours at which time the ether was removed at reduced pressure and the residue was placed under high vacuum overnight. Recrystallization of the remaining material from hexane gave 0.26 gram (0.928 mmole, 36% yield) of benzyl(fluoro)methyl(l-naphthyl)silane ( 129): mp 70.5-73 °C; NMR

(CDCI3 ) 0.57-0.60 (d, 3H, Si-CH 3 ) , 2.54-2.73 (octet, 2H, Si-CH 2 Ph) , 7.00-8.04 (m, 12H, aryl H) ; MS M+ 280.1079 (31.77%, C isH nFSi) , 189.0593 (100%, CllHioFSi). Anal. Calcd for CisH nFSi: C, 77.10%; H, 6.11%. Found C, 77.03%; H, 6.15%

Reactions of f+l-fBromomethvPrnethyin-naphthvPphenylsilane C81 with Varied Amounts of Tetrabutvlammonium Fluoride

Silane 8. was added to five separate flasks containing 0.20 ml of tetrahydrofuran; (A) 0.0627 gram (0.184 mmole), (B) 0.0634 gram (0.186 mmole), (C) 0.0622 gram (0.182 mmole), (D) 0.0629 gram (0.184 mmole) and (F) 0.334 gram (0.0979 mmole). Varied amounts 141 of tetrabutylammonium fluoride as a 1 M solution in tetrahydrofuran was added to A-D with stirring; (A) 0.184 ml (0.184 mmole), (B) 0.139 ml (0.139 mmole), (C) 0.091 ml (0.091 mmole) and (D) 0.046 ml (0.046 mmole). The solutions were stirred for 10 minutes and diluted to 1 ml with tetrahydrofuran. Optical rotational measurements (observed optical rotations) were then taken of each solution (A) +0.083°, (B) +0.102°, (C) +0.197°, (D) +0.320° and (F) +0.245°. Silica gel chromatography using 75% hexane-25% benzene solution gave 0.0184 gram of silanes £. and 129 isolated together (similar Rf values on silica gel) for reaction A in a ratio of 0.38/1 (8/1291. Similarly 0.0472 gram of silanes & and 129 were isolated together on silica gel in reaction D in a ratio of 5.69/1 (0.0413 grams £J 0.0059 grams JL2£). Ratios were calculated using NMR integration.

Reaction of (+)-('BromomethvPmethvin-naphthvPphenylsilane (81 with Tetrabutylammonium Fluoride

Silane £_ (0.1258 gram, 0.369 mmole) in 2 ml of tetrahydrofuran, was treated with a 1 M tetrabutylammonium fluoride solution (0.40 ml, 0.40 mmole) in tetrahydrofuran for 10 seconds at room temperature and immediately diluted in 100 ml of pentane at -78 °C. The solution was filtered cold and the solvent was removed at reduced pressure. The residue was chromatographed on silica gel using 75% hexane-25% benzene to obtain 0.0511 gram of a mixture of 8. and 129. isolated together. The mixture had an observed optical rotation of + 0 .100° in 1 ml of cyclohexane and 142 NMR integration indicated a 8/129 ratio of 1/4. The observed optical rotation is calculated to be due to unreact starting material 8. using integration of *H NMR.

Migratory Aptitude Study of Reactions of f+WBromomethvlV methvKT-naphthvllphenvlsilane f81 with Sodium Methoxide

Silane & (0.0630 gram, 0.185 mmole) and 0.119 gram (0.0022 mole) of sodium methoxide were added to 0.40 ml of dioxane. The mixture was stirred for 48 hours at which time thin layer chromatography indicate no 8. remained. A solution of 0.60 ml (0.60 mmole) of 1 M tetrabutylammonium fluoride in tetrahydrofuran was added and the mixture was stirred overnight. The standard, 0.0158 gram of anisole, was added and the solution was worked-up by adding 2 ml of water and extracting 4 times with 0.40 ml portions of pentane. Gas chromatographic analysis using internal standard methodology (injector temperature and detector temperature 260 °C, the oven temperature was 60 °C for 1.2 minutes and increased thereafter by 40 0 C/minute until 160 °C was reached) revealed: (1) toluene 1.02 min 0.149 mmole, 81% ; (2) anisole, 2.25 minutes, standard and (3) 1-methylnaphthalene, 4.41 minutes, 0.0157 mmole, 9% yield. In this reaction a small amount of naphthalene was observed in the GC trace of the reaction mixture before tetrabutylammonium fluoride was added. After the fluoride was added a large off scale presence of naphthalene was observed on the chromatographic trace. 143 Migratory Aptitude Study of Reactions of ('+WBromomethvlV methvin-naphthvDphenylsilane f 8)with Tetrabutylammonium F luoride

To silane £_ (0.0547 gram, 0.1603 mmole) in 0.20 ml of tetrahydrofuran was added 0.40 ml (0.40 mmole) of 1 M tetrabutylammonium fluoride in tetrahydrofuran and the solution was stirred overnight. The reaction mixture was worked-up by adding 2 ml of water and extracting 4 times with 0.40 ml portions of pentane followed by the addition of 0.0143 gram of anisole to the combined extracts. The solution was analyzed via gas chromatography using internal standard methodology (injector temperature and detector temperature 260 °C, oven temperature 60 °C for 1.2 minutes increasing thereafter by 40 °C/minute until 160 °C) revealing: (1) toluene 1.02 minutes 0.133 mmole, 83% ; (2) anisole, 2.25 minutes, standard and (3) 1-methylnaphthelene, 4.41 minutes, 0.012 mmole, 8% yield). These reactions show a large off scale presence of naphthalene on the gas chromatographic trace. The amount of naphthalene was not quantified.

Reaction of BenzvKfluorolmethyKT-naphthvllsilane 129 with Tetrabutylammonium Fluoride

Silane 129 (0.0403 gram, 0.144 mmole) in 0.20 ml of tetrahydrofuran, was treated with 0.30 ml (0.30 mmole) of 1 M tetrabutylammonium fluoride in tetrahydrofuran. The solution was stirred overnight and worked up by adding 2 ml of water and extracting 4 times with 0.40 ml of pentane. The standard, anisole (0.0160 gram), was added to the combined extracts and the solution 144 was analyzed on the gas chromatograph (injector temperature and detector temperature 260 °C, oven temperature 60 °C for 1.2 minutes increasing thereafter by 40 0 C/minute until 160 °C ) revealing: (1) toluene, 1.02 min 0.137 mmole, 95% and (2) anisole, 2.25 minutes, standard. A large off scale presence of naphthalene was also observed on the gas chromatographic trace. LIST OF REFERENCES

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