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11-1-1991 Hydroboration-oxidation of styrene, 2,3 dihydrofuran and quadricyclene dimethylester promoted by Wilkinson's catalyst Pingyun Feng
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Recommended Citation Feng, Pingyun, "Hydroboration-oxidation of styrene, 2,3 dihydrofuran and quadricyclene dimethylester promoted by Wilkinson's catalyst" (1991). Thesis. Rochester Institute of Technology. Accessed from
This Thesis is brought to you for free and open access by the Thesis/Dissertation Collections at RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. HYDROBORATION-OXIDATION OF STYRENE, 2,3-DIHYDROFURAN AND QUADRICYCLENE DIMETHYLESTER PROMOTED BY WILKINSON'S CATALYST
PINGYUN FENG
NOVEMBER,1991
THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
APPROVED:
Terence C. Morrill Project Adviser
Gerald A. Takaer Department Head
Library
Rochester Institute of Technology Rochester, New York 14623 Department of Chemistry Title of thesis
Hydroboration-oxidation of Styrene, 2,3-Dihydrofuran and Quadricyclene
Dimethylester Promoted by Wilkinson's Catalyst
I Pingyun Feng hereby grant permission to the Wallace Memorial Library of RIT to reproduce my thesis in whole orin part. Any reproduction will not be for conunercial use or profit.
Date: Nov. 25 , 1991
Pingyun Feng Table of Contents
Acknowledgments
Abstract
Introduction 1
Mechanism of Hydroboration-oxidation 2
Catecholborane 4
Wilkinson's Catalyst 7
Mechanism of Hydrogenation with Wilkinson's Catalyst 9
Hydroboration of Styrene 10
Hydroboration of Heterocyclic Olefins 12
Hydroboration of a Cyclopropane Ring in the Quadricyclene System 15
Experimental 19
Hydroboration-oxidation of Styrene 21
Hydroboration-oxidation 2,3-Dihydrofuran 31
Preparation of Quadricyclene Dimethylester 34
Preparation of Quadricyclene Dicarboxylic acid 39
Results and Discussion 42
Hydroboration of Styrene with BH3THF 42
Hydroboration of Styrene with Catecholborane 44
Hydroboration of Styrene Promoted by Wilkinson's Catalyst 44
Mechanism of Rhodium Catalyzed Hydroboration of Olefins 48
Hydroboration of 2,3-Dihydrofuran Promoted by Wilkinson's Catalyst.... 54
Hydroboration of Cyclopropane Ring in Quadricyclene System 57 Spectra 300 MHz !H NMR of Norbornadiene Dimethylester in CD3COCD3 6 1
200 MHz XH NMR of Norbornadiene Diacid in CD3COCD3 62
200 MHz lH NMR of Quadricyclene Diacid in DMSO 63
GC - Mass Spectrum of the Reaction of Styrene and BH3THF without Wilkinson's Catalyst 64
GC - Mass Spectrum of the Reaction of Styrene and BH3THF with Wilkinson's Catalyst 65
GC - Mass Spectrum of the Reaction of Styrene and Catecholborane without Wilkinson's Catalyst 66
GC - Mass Spectrum of the Reaction of Styrene and Catecholborane
with Wilkinson's Catalyst (reaction time 0.5 hr.) 67
GC - Mass Spectrum of the Reaction of 2,3-Dihydrofuran and BH3THF without Wilkinson's Catalyst 68
GC - Mass Spectrum of the Reaction of 2,3-Dihydrofuran and BH3THF with Wilkinson's Catalyst 69
Capillary GC Spectrum of Authentic a - Phenylethanol Sample 70
Capillary GC Spectrum of Authentic P - Phenylethanol Sample 7 1
Capillary GC Spectrum of the Reaction of Styrene and Catacholborane with Wilkinson's Catalyst (reaction time 1 hr. ) 72
Capillary GC Spectrum of the Reaction of Styrene and Catacholborane with Wilkinson's Catalyst (reaction time 0.5 hr. ) 73 Introduction
dienes2 The remarkable facile addition of diborane in ether solvents to olefins1,
acetylenes3 Brown.4 and at room temperature was discovered in 1956 by Herbert C.
The reaction, hydroboration, makes readily available a wide variety of organoboranes which are proving to be exceedingly useful in organic synthesis. A wide variety of olefins, amines, ketones and particularly, alcohols of desired structure and
sequence.5 stereochemistry have been prepared by the hydroboration - oxidation
Pretiminary observations indicated that the addition to an unsymmetrical olefin proceeds to place the boron atom on the less substituted of the two carbon atoms forming the double bond6. Since the organoborane is readily converted to the corresponding alcohol by oxidation with alkaline hydrogen peroxide, hydroboration provides a simple convenient synthetic route for the anti-Markovinikoff hydration of olefins.
Recently, several groups (RIT, Harvard, Rice, Germany) have applied transition metal catalysis to hydroboration resulting in rate enhancements for less reactive borane reagents as well as complementary or improved regio- and stereochemistry. The possibility has been raised that transition metal catalysis might
reaction.7 significantly extend the utility of the hydroboration
1 Brown, H. C.,and Zweifel, G., /. Org. Chem., I960, 82, 4708.
2 Brown, H. C.,and Zweifel, G., /. Org. Chem., 1959, 81, 5832.
3 Brown, H. C.,and Zweifel, G., /. Org. Chem., 1959, 81, 1512
4 Purdue University, Nobel Prize Laureate 1979.
5 Ruffing, C. J., Aldrichimica Acta, 1989, 22, 3, 80
6 Brown, H. C.,and Zweifel, G., J. Org. Chem., 1960, 82, 4708.
7 Chem. Soc. Evans, D. A. Fu, G. C. , and Hoveyda, A. H. , /. Am. 1988, 770, 6917. Borane, BH3, is an avid electron pair acceptor because only a sextet of valence electrons is present at boron in the monomelic molecule. The pure neat material exists
dimer.8 as a Diborane can be generated in situ from sodium borohydride and boron trifluoride. In aprotic solvents which act as electron pair donors such as ethers, tertiary amines, and sulfides, tetrahydrofuran,we have known that diborane forms stable Lewis acid-Lewis base complexes.
+ 2R20 ' B2H6 -2BH3 . 1 2R2Q BH3
Solutions of BH3-THF complex in tetrahydrofuran are commercially available.
An alternative commercially available borane reagent is the borane-dimethyl sulfide
complex. Both hydroboration reagents BH3THF and BH3-SMe2 react rapidly with
unsaturated carbon - carbon bonds and do not require metal or other catalysis.
Mechanism of Hvdroboration-Oxidation
Hydroboration is not only stereospecific ( syn addition ) but also regioselective;
steric and electronic factors control the regioselectivity: the boron atom binds to the less hindered ( less substituted ) carbon, and the hydrogen atom binds to the more
substituted carbon.
Because the k bond in a carbon - carbon double bond is electron rich and borane is electron poor, it is reasonable to formulate an initial Lewis acid base complex, requiring the participation of the empty p orbital on BH3, as in the borane -
8 Carey, F. A. and Sunderrg, R. J., Advanced Organic Chemistry, Plenum Press, New York 1983,
167. ether complex. Subsequently, one of the hydrogens is transferred by means of a four centered transition state to one of the alkene carbons. All three B-H bonds are reactive in the same way and therefore trialkylboranes are formed. Then the trialkylboranes are oxidized with basic aqueous hydrogen peroxide; the highly nucleophilic and electron - rich hydroperoxide ion attacks the electron - poor boron atom. The resulting intermediate undergoes a rearrangement in which an alkyl group migrates with its electron pair keeping the same configuration to the neighboring oxygen, displacing a hydroxide group in this process. Although the hydroxide ion is usually a poor leaving group, the reactive O-O bond and the simple intermolecular nature of this reaction allows it to leave. The initial product R2BOR undergoes further similar oxidations to a trialkyl borate (RO)3B which is hydrolyzed by the basic aqueous medium to the alcohol
(ROH) and sodium borate.9.
This mechanism is shown below:
R
I - - NaOH r^- O + :0-OH R B OH 777^H2U R R
R
HOO" HOO-
-? B ? aa* OH- R
OH" - - - OH OR
9 Vollhardt,K. C, Organic Chemistry, W. H. Freeman and Company, New York, 1987, 479. R
' NaOH - r~^.
+ - :0 OH TT ^ R B O OH H20
R
R
HOO" HOO"
-? R B ? a** - OH OH" OH - OR
In addition to borane reagent, there are other hydroboration reagents which are
available such as disiamylborane, 9 - BBN, catecholborane, and chloroborane. One of the more interesting is catecholborane (1,3,2-benzodioxaborole).
Catecholborane
Catecholborane (CB) is readily available from the reaction of catechol with borane complex in THF10:
10 Brown, H. C. and Gupta, S. K., /. Am. Chem. Soc. 1975, 97, 5249. OH THF
+ THF BH: 25" OC 0 - C OH
( CB )
In catecholborane, the boron atom is part of a planar five-membered ring. It has unique structural features and is only a mild hydroboration agent due to competing electron donation from the adjacent oxygen in the five-membered ring. It is a much weaker Lewis acid than the borane complex. Hydroboration with catecholborane is usually very slow at room temperature, while at high temperature the hydroboration
C.11 proceeds at much more satisfactory rate. It hydroborates olefins at 100 It reacts
C.12 with acetylenes at 70
CHR' RCH = CH-CH2R' B
100
B H
RC^CR'
70'
Several groups have now applied transition-metal catalysis to hydroboration resulting in rate enhancement for less reactive boron reagents, such as
1 1 Brown, H. C. and Gupta, S. K., /. Am. Chem. Soc. 1971, 93, 1816. 12 Brown, H. C. and Gupta, S. K., /. Am. Chem. Soc. 1972, 94, 4370. catecholborane13. For example, without a catalyst, two above reactions require temperature of 100C and 70C respectively; however, they can occur without difficulty at room temperature in the presence of a catalyst. Mannig and Noth have found that it is possible to activate the carbon-carbon double bonds of olefins so strongly that they are preferentially hydroborated even in the presence of the much more reactive keto group.14 For example, without a catalyst, 5-hexen-2-one reacts with
2-(l-methyl-4-pentenyloxy)-l,3,2- catecholborane (1) rapidly and quantitatively give
whereas presence of benzodioxaborole (2) , in the Wilkinson's catalyst, RhCl(PPh3)3, the ketone (3) is preferentially formed:
OC>--w Oc>- + ^Y< > 0 oa\ Q-\^^
In addition to Wilkinson's catalyst, the complexes [RhCl(CO){P(C6H5)3}2],
= [RhCl(CO){ As(C6H5)3h], and [RhCl(cod)]2 (cod 1,5 -cyclooctadiene) are also
suitable as catalysts for hydroboration with CB, but complexes of platium, palladium,
effects.14 iridium, and cobalt exhibit no or only minor catalytic We use Wilkinson's
catalyst in our experiments, the reagent that is convenient because it is stable in air and
yet exhibits high reactivity.
13 Ruffing, C. J. Aldrichimica Acta, 1989, 22, 80. 14 Mannig, D. and Noth, H., Angew. Chem. Int. Ed. Engl, 1985, 24, 878. Like the keto group, other function groups such as hydroxy-, cyano-, nitro-, chloro-, azo-. ether, ester, and carboxylic acid groups are also not effected by
Wilkinson's catalyst under these conditions.
Wilkinson's Catalyst
Two independent reports15 appeared in 1965 that the complex chlorotris(triphenylphosphine)rhodium(l), RhCl(PPh3)3, in organic solvents is an active catalyst for reduction of alkynes and alkenes at ambient temperature and atmospheric pressure. This compound has subsequently become known as Wilkinson's catalyst. Its X-ray structure16 is shown below ( Fig. 1 ).
15 Young, J. F., Osborne, J. A., Jardine, F. H., and Wilkinson, G. /. Chem. Soc. Chem.
Commun., 1965, 131; Coffey, R. S., ICI Ltd. Br. Pat., 1965, 1, 121. 16 Huheey, J. E., Inorganic Chemistry, Third edition, Harper & Row, Publishers, New York,
1983, 655. Figure 1. X - ray structure of Wilkinson's catalyst:
&.***!E5SS2ESS5F (*'p,'Rha *-> '- *-*.*~*-*-.
In this structure, RhCl(PPh3)3 has 16 electrons in Rh valence shell, the dimer or the 5-co-ordinate complex of RhOQ?Ph3)4 does not form during preparation due to the excess of triphenylphosphine in the solution and the steric factor (large phenyl groups). Actually, the dimer can be readily converted to RhOQ?Ph3)3 by heating with a
ethanol.17 10 molar excess of triphenylphosphine in
The tristriphenylphosphine halide dissociates in solution as shown:
Ethanol RhCl(PPh3)3- a** RhCl(PPh3)2 + PPh3
17 Osborn, J. A., Jardine, F. H., Young, J. F. and Wilkinson, G., J. Chem. Soc. (A) 1966, 1711 The essential point is that RhCl(PPh3)2 has vacant coordination sites which can be occupied either by weakly bound solvent molecules or by other ligand atoms. The existence of vacant sites is essential to the catalytic activity of RhClQ?Ph3)2 as we shall see below from the mechanism.18
Mechanism of Hvdrogenation with Wilkinson's Catalyst
The mechanism of hydrogenation includes three major steps: oxidative-addition, insertion, and reductive-elimination
Figure 2 : Mechanism of Hydrogenation with Wilkinson's Catalyst
H H
/H Ph3P H H2 \ I . Solvent !| - (Ph3P)3RhCl ^=^ \Rh/ 16e \^ ciPh3 Solvent ige 18e
18 J. A - Interscience Publication 1985 Pearson, Metallo-organic Chemistry , Wiley H H H H, C-C-H Ph3P. | Ph.P Insertion %/iA CI ^ / I ^Ph3P CI / Ph.P c" ^C = 18e 16e
- Alkane Ph3P Solvent Red.- Elimin. Rh (Ph3P)3RhCl a/ NPh^P 16e
16e
The mechanism of hydroboration promoted by Wilkinson's catalyst is not yet completely understood. A mechanism similar to hydrogenation has been suggested. We will discuss this in more detail in Results and Discussion section.
Hydroboration - Oxidation of Stvrene
The hydroboration of simple terminal alkenes such as 1-butene, 1-pentene and
1-hexene with diborane in THF proceeds in a highly regioselective manner to give predominant addition of the boron atom to the terminal carbon atom ( ~ 93 - 94 % ).
Only a minor amount of addition to give the secondary alkyl boron product is observed
( ~ 6 - 7 % )19. These results correspond to a predomination of anti-Markovnikov
I9 Brown, H. C. and Zweifel, G. /. Org. Chem., 1960, 82, 4708
10 addition. The hydroboration of terminal alkenes with an alkyl substituted at the 2- position, such as isobutylene, proceeds to give almost exclusively ( 99% ) the terminal hydroboration products20. On the other hand, the hydroboration of another terminal alkene, styrene, results in only 81% of the boron atom entering the terminal position, reflecting the significant non-steric directive influence of the phenyl substituted.21
It became of interest to investigate such directive effects in the hydroboration of alkenes with catecholborane. In 1975 H. C. Brown and S. K. Gupta investigated such directive effects in the hydroboration of styrene with catecholborane at 100C. The results indicated that catecholborane is more selective than borane in placing the boron atom preferentially at the less hindered carbon atom.21 For example, they used 1- decene, 1-diisobutylene, norbomene and styrene for their experiments. After the standard hydroboration with catecholborane ( 10 % excess ) at 100C, the product organoborane was then oxidized with alkaline hydrogen peroxide. The following results were obtained:
CH3 CH3 I I CH3(CH2)7CH=CH2 CH3C- CH2- C = CH2 I CH, t t 1% 99% 2% 98%
" 20 Brown, H. C. Hydroboration ", W. A. Benjamin, New York, 1962 21 Brown, H. C. and Gupta, S. K., /. Am. Chem. Soc. 1975 , 97, 5249.
11 99.5%
0.5%
The above results indicate that catacholborane is somewhat more selective than borane in placing the borane in less hindered carbon atom. Even the directive effect of the styrene changed from 80% with borane to 92% with catacholborane.
It was of greater interest to investigate hydroboration of styrene and other alkenes with Wilkinson's catalyst. Some very interesting results have been obtained and we will discuss them in more detail below.
Hydroboration of Heterocyclic Olefins
Heterocyclic derivatives introduce some major differences in hydroboration- organoborane reactions. First, the heterocyclic atom plays a major role in controlling the direction of hydroboration of double (and triple) bonds. Secondly, the presence of a
(3- opening:22 boron atom to the heteroatom can result in facile ring For example:
22 Brown, H. C. and Rangaishenvi, M. V. J. Heterocyclic Chem., 1990, 27, 13.
12 OH I / + .BR2 R2BH NaOH V Na r O o O /
/ +
R2BOH Na
O O I / HO-BR2
Ring opening can be thought of as a elirnination from the intermediate in the reaction below. The extent of ehmination depends upon a number of factors, such as leaving group (X), temperature and solvent.23
X B-H \ RCH= CHX RCHCH2X- RCH=CH2 + B-X I
If X is a good leaving group, such as CI, or OAc, the ehmination occurs rapidly.24'25'26 Elimination is minimized for poor leaving groups, such as OR and
OAr. It was observed that such hydroboration can proceed with a remarkable
23 Brown, H. C. Vara Prasad, J. V. N., and Zee, S. H., /. Org. Chem. 1985, 50, 1582.
24 Brown, H. C, Unni, M. K. /. Am. Chem. Soc. 1968, 90, 2902.
25 Brown, H. C, Gallivan, R. M, Jr. /. Am. Chem. Soc. 1968, 90, 2906.
26 Brown, H. C, Sharp, R. L. /. Am. Chem. Soc. 1968, 90, 2915.
13 regioselectivity, placing essentially all of the boron atom at the (3 - position27,28. For example, l-ethoxy-2-methyl-l-propene yields 88% l-ethoxy-2-methyl 2-propanol
p- upon hydroboration-oxidation, indicating the preference of the boron atom for a carbon atom even though it is tertiary.29
CH3 CH3 I ' '* n NaOH, H202 ^B-H L_i_i rH3r=rHor:H: , ch3cch2oc2h5
P a /Bx
CH3 I CH3CCH2OC2H5
OH
Although there have been individual reports on the hydroboration of
olefins oxygen,30 sulfur,31 and nitrogen32'33 clear heterocyclic containing , understanding of the optimum conditions required for clean and efficient hydroboration of heterocyclic olefins is still lacking.
27 Pasto, D. J. and Cumbo.C. C, /. Am. Chem. Soc. 1964, 86, 4343. 28 Zweifel, G., and Plamondon, J., /. Org. Chem. 1970, 35, 898. 29 Brown, H. C, and Sharp, R. L., /. Am. Chem. Soc. 1968, 90, 2915.
30 Still, C, Goldsmith, W. Jr., /. Org. Chem. 1970, 35, 2282.
3i Org. Chem. 95. Krug, R. C, Boswell, D. E. , /. 1962, 27,
32 Caron-Sigaut, C, Le Men-Oliver, L., Hugel, G., Levy, J., Le Men, J. Tetrahedron 1979, 35,
957.
33 Shono, T., Matsumura, Y., Tsubata, K., Sugihara, Y., Yamane, S., Kanazawa, T., Aoki, T. /.
Am. Chem. Soc. 1982, 704, 6697.
14 So it became of interest for us to study the hydroboration of heterocyclic olefins and hydroboration of heterocyclic olefins promoted by Wilkinson's catalyst. We chose
2,3 - dihydrofuran for our study.
Hydroboration of a Cyclopropane Ring in the Quadricyclene System
Many chemical reactions of quadricyclene system have been studied.34'35'36
Hydroboration-oxidation of the cyclopropane ring of this system is a very new area.
The cleavage of cyclopropane in norcarane by neat diborane has been reported by
Wood.37 Rickborn and The reaction is quite regioselective and the products were those
involving boron addition to the least-substituted carbon, and hydrogen to the most-
substituted carbon (Markovnikov addition). Some examples are given here.
34 Nikolai S. Zefirov, N. K. Sadovaya, T. N. Velikokhat'ko, L. A. Andreeva, and Terence C.
Morrill, /. Org. Chem. 1982, 8, 47.
35 Stanley J. C. and Robert L. S., /. Am. Chem. Soc. 1958, 80, 1950.
36 McCulloch, A. W., Mcinnes, A. G., Smith, D. G. and Walter, J. A. Can. J. Chem. 1976, 54,
2014
37 Rickborn, B. and Wood, S. E. /. Am. Chem. Soc. 1971, 93, 3940
15 OH
1. B2H6,107; OH" CH2OH 2.H202,
95% 5%
OH
0 %
This reaction is a highly regioselsctive cleavage process with only 5% of
cyclohexanol formed due to the cleavage of the internal bond.
1.B2H6>105,1 hr OH
2.H202OH" OH
95% 5%
We plan to use quadricyclene dimethyl ester for our study. Some chemical properties of this system have been studied. Early work clearly describes the
16 - propensity for C5 Q; or C1 -C7 ( shown in compound 4 ) bond cleavage in this
system.38
COOH
COOH
(4)
For example, addition of bromine to this system has been reported to give (6)
and (5),
COO]
(5) (6)
38 /. Org. Cristol, J., Harrington, J. K., Morrill ,T. C. and greenwald, B. E., Chem., 1971, 36,
2773
17 The C-3 carboxylic group was shown to be endo by the ready formation of lactone (6). Structure (5) with exo- Br at the secondary halide position appeared to be reasonable, as it permitted the formation of (6) by a stereochemically expected inversion
process.39
Other examples such as addition of benzenesulfenyl chloride to quadricyclene
- cleavage dicarboxylic acid and dimethyl ester also revealed the C5 -Q ( Ci C7 ) bond propensity in this system.40
39 Cristol, S.J., Harrington, J. K. and Singer, M. S., /. Am. Chem. Soc. 1966, 88, 1529
40 Morrill, T. C, Malasanta, S. Warren, K. M. and Greenwald, B. E., /. Org. Chem., 1975, 40,
3032
18 Experimental
Nuclear magnetic resonance spectra were obtained using either a Bruker
FT-NMR spectrometer (200 MHz ); or a G. E. QE (300 MHz). Tetramethylsilane
(TMS) was used as a reference standard, and all chemical shifts were recorded in 8 units (ppm) related to TMS (8 = 0.00 ppm). Multiplicity notations are: s, singlet; d, doublet; t, triplet.
The GC Mass Spectrometric Analyses were performed on a Hewlett Packard
5995 GC/MS with a Supeleco fused silica capillary SPB-1 non-polar column ( 30 m,
0.32 mm ID, 1.0 mm df ). Helium was used as the carrier gas.
Capillary Gas Chromatography spectra was performed on a Hewlett Packard
5890A with a 50m x 0.32mm x 0.25 (J.m HP-1 ( cross linked methyl silicone gum ) non-polar column. Helium was used as the carrier gas. Flame ionization detector was
used.
Mel-Temp Melting points were determined using a apparatus from Lab
Specialties Incorporation, and required no correction as per calibration by benzoic acid.
Pyrex Photochemical reactions were carried out using a 1 -liter photochemical reaction vessel and a 450-Watt high pressure mercury vapor lamp QZnglehard Hanovia,
Inc.) was placed in a quartz immersion well. The quartz immersion well was placed in
19 the reaction jacket. The diagram of the 1-liter Pyrex photochemical reaction vessel was shown in Figure 3.
Dry nitrogen was prepared by passing reagent grade nitrogen from Linde Air
Products through Fieser's reagent ( see experiment 3 ) followd by passage through concentrated sulfuric acid and anhydrous potassium hydroxide.
Chemicals and solvents were purchased from Aldrich Chemical Co., Sigma
Chemical Co., Fisher, and Baker.
20 Hydroboration-oxidation of Stvrene
1. Hydroboration-oxidation of Styrene with BH-yTHF
All glassware was predried in an oven at 150 overnight, assembled hot, and
dry,41 allowed to cool under a stream of deoxygenated nitrogen42. The nitrogen gas was purified by Fieser's solution43, NaOH, and H2SO4.
A dry three-necked 250 ml flask was equipped with a magnetic stirring bar, a
condenser, and a pressure-equalizing dropping funnel. After cooling down to room
temperature under a stream of nitrogen, the flask was charged with 2.08g ( 20 mmol )
of styrene by removing the condenser and adding the styrene as quickly as possible
under a blanket of nitrogen. The system was then reflushed with nitrogen for several
minutes, and 20 ml ( 20 mmol ) of BH3-THF ( 1.0 M THF solution ) was added to the
dropping funnel with a syringe.
Hydroboration was achieved by the slow dropwise addition of the BH3-THF
solution to the flask. Following the addition, the colorless reaction mixture was stirred
at the room temperature for 1 hour. The reaction mixture was then cooled in an ice bath
and 10 ml of a 30% H2O2 solution and 10 ml of 3M NaOH solution was added to the
reaction flask. Care was taken to maintain the solution slightly alkaline ( pH ~ 8 ). The
reaction was stirred for 3 hours and the reaction temperature was allowed to reach room
temperature.
4i Brown, Herbert C. Organic Syntheses Via Boranes, A Wiley-Interscience Publication, John Wiley
& Sons, 1975
42 See experiment 2
43 See experiment 3
21 Then anhydrous ethyl ether (3 x 20) ml was used to extract the alcohol products. The combined ether extracts were washed with a 20 ml of saturated sodium bicarbonate solution and then 2x20 ml of distilled water; the ether layer was subsequently separated and dried over anhydrous magnesium sulfate.
The product mixture was analyzed by GC/MS spectrometry and compared with authentic sample from Aldrich.
Mass spectrum of C6H5CHOHCH3 (9) : m/z 79 (100%), m/z 107 (84%), m/z
122 (28%), m/z 43 (42%), m/z 51 (30%), m/z 27 (11%). Retention time as shown on
GC/MS spectra was: 1.674 min .
Mass spectrum of C6H5CH2CH2OH (8) : m/z 91 (100%), m/z 122 (28%), m/z 65 (25%), m/z 31 (10%). Retention time as shown on GC/MS spectra was: 1.782 min.
OH OH
l.BH3-THF, RT, lh 2.H202, NaOH V
80.7% 19.3%
(7) (8) (9)
The total yield for this reaction was 78.9%. The yield was determined by
the of weight after evaporating solvent and multiplying by GC percentage products (8) and (9); GC identification was done by using authentic (Aldrich) samples of (8) and
(9).
22 2. Preparation of Dry. Deoxygenated Nitrogen
Bottled nitrogen was bubbled through a series of traps. The first one contained
solution44 Fieser's for the adsorption of oxygen. The second one was empty to prevent crossover. concentrated The third and fourth traps contained , respectively, sulfuric acid and sodium hydroxide pellets. Those last two traps were for removal of water vapor.
Solution44 3. Preparation of Fieser's
The solution was prepared by dissolving 20 g of potassium hydroxide in 100
ml of water and adding 2 g of sodium anthraquinone - p - sulfonate and 15 g of sodium
hyposulfite ( Na2S204 ) to the warm solution. The mixture was stirred until a clear,
blood-red solution results and this red solution was allowed to cool to room
temperature. Traces of oxygen in the nitrogen were removed by passage of the gas through a trap containing this solution.
The above procedure was applied to all of our hydroboration-oxidation
reactions.
44 Fieser, L. F., Fieser, M. Reagents For Organic Reactions, John Wiley and Sons: New York
1967; p 393.
23 4. Hydroboration-oxidation of Styrene using BHvTHF
with Wilkinson's Catalyst
All the set-up, nitrogen, and glassware went through the same procedures as
described in experiment 1.
A dry three-necked 250 ml flask was charged with 2.08 g ( 20 mmol ) styrene.
The system was then reflushed with nitrogen for several minutes, and 0.04 g ( ~ 0.2%
mol ) Wilkinson's catalyst was added to this reaction flask. Following that addition, 20
ml ( 20 mmol ) BH3-THF ( 1.0 M THF solution ) was added to the dropping funnel
with a syringe, then added dropwisely to the reaction flask. The reaction mixture was
stirred at the room temperature for 1 hour, cooled in an ice bath, and then 10 ml of a
30% H2O2 solution and 10 ml of 3M NaOH were added to the reaction mixture. Care
was taken to keep the solution slightly alkaline. The reaction mixture was stirred for 3
hours and the resulting product was allowed to reach room temperature.
Extraction of the alcohol products was carried out with 3 x 20 ml of anhydrous
ethyl ether. The combined ether extracts were washed with 20 ml of saturated sodium
bicarbonate solution and 2 x 20 ml of distilled water. Then the ether layer was
separated and dried over anhydrous magnesium sulfate.
The product mixture was analyzed by GC/MS spectrometry. Mass spectra of
C6H5CHOHCH3 and C6H5CH2CH2OH were same as the previous experiment. The retention times as shown on GC/MS spectra were 1.770 min for (9) and 1.902 min for
(8). The mass spectra were compared with those from authentic samples from Ardrich
company.
24 BH3-THF, RT, lh NaOH, H202 -a*- **~ tzt: Wilkinson's Cat. H,0
OH OH y
65.9% 34.1%
(8) (9)
The total yield of alcohol for this reaction was 67.1% . The yield was determined by total weight of product after evaporating solvent and multiplication by the GC percentage of products (8) and (9) in the total product mixture.
25 5. Hydroboration-oxidation of Styrene with Catecholborane
Nitrogen and glasswares was subjected to the same procedure as described in experiment 1.
A dry three-necked 250 ml flask was equipped with magnetic stirred bar and a
condenser. After cooling the system to room temperature under a nitrogen stream, 5 ml
of the fresh dry THF was added to the reaction flask, the system was then flushed
again with nitrogen for several minutes, and finally the flask was charged with 2.08 g
( 20 mmol ) styrene and 2.40 g ( 20 mmol ) of catechoborane as quickly as possible
under a blanket of nitrogen. The reaction mixture was stirred at room temperature for 1
hour, cooled in an ice bath, and to this was added dropwise 10 ml of a 30% H2O2
solution and 10 ml of 3M NaOH solution. Care was taken to maintain the solution at a
slightly alkaline pH ( ~ 8 ). The reaction mixture was stirred for 3 hours and the
reaction mixture was allowed to reach room temperature.
Anhydrous ethyl ether (3 x 20 ml) was used to extract the alcohol products. The
combined ether extracts were washed with 2 x 20 ml of saturated sodium bicarbonate
solution, and 20 ml of distilled water, and then the ether layer was separated and dried
over anhydrous magnesium sulfate.
The product mixture was analyzed by GC/MS spectrometry. Mass spectra of
C6H5CHOHCH3 and C6H5CH2CH2OH were same as the previous experiment. The retention times ( GC/MS ) were 1.982 min and 2.437 min respectively. And the Mass
spectra were compared with authentic sample from Aldrich company.
26 o \ RT,lh CT- W-
OH OH y NaOH, H202 y^V S^ v^
73.7% 26.3%
(8) (9)
Only 3.8% of the styrene was consumed. This result was measured by GC.
27 6. Hydroboration -oxidation of Styrene using Catechoborane
with Wilkinson's Catalyst
The setup, nitrogen, and all glassware went through the same procedures as described in experiment 1.
The 250 ml flask was charged with 5 ml of fresh THF and 2.08 g (20 mmol )
styrene was added under a stream of nitrogen, then 2.40 g ( 20 mmol ) of
catecholborane and 0.04 g ( ~ 0.2% mol ) Wilkinson's catalyst was added to the reaction flask. The reaction mixture was stirred at the room temperature for 1 hour,
cooled in an ice bath, and then 10 ml of a 30% H2O2 solution followed by 10 ml of 3M
NaOH were added to the flask. The reaction mixture was stirred for 3 hours with
cooling and the reagents was allowed to reach room temperature.
Anhydrous ethyl ether 3 x 20 ml was used to extract the alcohol products. The
combined ether extracts were washed with 20 ml of saturated sodium bicarbonate
solution and then 2 x 20 ml of distilled water; the ether layer was separated and dried
over anhydrous magnesium sulfate. The product mixture was analyzed by GC/MS
spectrometry. Mass spectra of C6H5CHOHCH3 and C6H5CH2CH2OH were same as
the previous experiment. The GC/MS retention times were respectively, 1.864 min and
2.026 min
The product mixture was also analyzed by gas chromatography ( HP 5890A )
The retention times for authentic samples of C6H5CHOHCH3 (9) and
C6H5CH2CH2OH (8) ( Aldrich company ) were 4.787 min and 5.084 min. The retention times for the reaction product mixture were respectively, 4.779 min and 5.078 min, clearly in good agreement with the authentic samples.
28 RT, 1 h B-H Wilkinson's Cata.
OH OH
NaOH, H,02^2 V
14.1% 85.8%
(8) (9)
The total yield of this reaction was 71.5%. The yield was determined by the same method as in experiment 1.
29 If the reaction time was reduced to half an hour different results were obtained.
0.5 h B-H RT, Wilkinson's Cata.
OH OH y NaOH, H202
3.1% 96.9%
(8) (9)
The product mixture was again analyzed by gas chromatography ( HP 5890A ).
The retention times for standard samples of C6H5CHOHCH3 and C6H5CH2CH2OH ( from Ardrich company ) were 4.787 min and 5.084 min. The retention times for reaction product mixture were respectively, 4.776 min and 5.075 min. The yield of this reaction was 59.1%. The work up and yield determination were same as in previous experiment.
30 Hvdroboration-oxidation of 2.3-Dihvdrofuran
Hydroboration-oxidation of 2. 3-Dihydrofuran with BHq-THF
All the glassware was predried in an oven at 150C for 24 hours, assembled hot, and allowed to cool under a stream of nitrogen ( purified by Fieser's solution,
NaOH, H2SO4 ).
A 250 ml flask was equipped with a magnetic stirring bar, a reflux condenser, and pressure-equalizing dropping funnel. After cooling to room temperature under a nitrogen stream, the reaction flask was charged with 10.5 g (150 mmol) or 3.5 g
(50 mmol) of 2,3-dihydrofuran by removing the condenser and adding the 2,3- dihydrofuran as quickly as possible under a blanket of nitrogen; the system was then flushed again with nitrogen for several minutes, then 50 ml ( 50 mmol ) of BH3THF complex ( 1.0 M THF solution ) was added to the dropping funnel with a syringe.
Hydroboration was achieved by the slow dropwise addition of the BH3THF solution to the flask. Following addition, the clear, colorless reaction mixture was stirred at room temperature for 2 hours to complete the reaction. At this point 50 ml of
3M aqueous sodium hydroxide was added to the reaction mixture. Then 25 ml of 30% aqueous hydrogen peroxide was introduced into the dropping funnel and added dropwise to the stirred reaction mixture at a rate such that the temperature of the reaction mixture did not exceed approximately 50C. The reaction mixture was stirred at room temperature overnight.
Anhydrous ethyl ether (3 x 50 ml) was used to extract the products, and the
combined ether ether was evaporated extracts were dried over anhydrous MgS04 , The
31 in 10.51 of resulting g crude product. GC/MS spectroscopy results are shown in tables
1 and 2 below.
3 BH3 THF H202, NaOH OH
HOCH2CH2CHCH3
( 12 )
+ CH^=CHCH?CH9OH2^n2v HOCH2CH2CH2CH2OH
( 13 )
( H )
Table 1 : Hydroboration-oxidation of 2,3-dihydrofuran
ratio of
reactants % 10 % 11 % 12 & 13 % yield 3:1
4.4 38.4 uncatalyzed 73.4 22.3
7.6 catalyzed 81.5 10.9 26.6
"catalyzed" Note : In Table 1, the ratio of 2,3-dihydrofuran to BH3-THF is 3: 1, and
means Wilkinson's catalyst was used in the reaction.
32 Table 2 : Hydroboration-oxidation of 2,3-dihydrofuran
ratio of reactants % 10 % 11 % 12 & 13 % yield 1:1
66.1 uncatalyzed 55.0 41.8 3.7
50.2 catalyzed 50.0 47.2 2.8
"catalyzed" Note : In Table 2, the ratio of 2,3-dihydrofuran to BH3-THF is 1:1, and
means Wilkinson's catalyst was used in the reaction.
33 Preparation of Dimpthvl Bievclor2.2.11hepra-2.5-diene-2.3-
Dicarboxylate
>0, 178UC 2
qooch3
CH2C12 -? COOC H
OOCH3 COOC H3
(14)
A fractional distillation apparatus was set up in the hood with a 200 ml round bottomed flask, to which was added 40.0 g ( 0.30 mol ) of dicyclopentadiene. A 400 ml receiving flask was attached and in this was placed 77 g ( 0.54 mol ) of dimethyl acetylenedicarboxylate dissolved in 250 ml CH2C12. The dicyclopentadiene was slowly heated to avoid the distillation of the dimer. And cyclopentadiene (b.p.45-47C) was distilled into the receiving flask in a dropwise fashion. The reaction mixture was allowed to stand overnight at room temperature.
34 evaporator 113.00 of pale yellow oil Upon evaporating the solvent ( rotary ) , g
-2,5- ( in quantitative yield and identified !H NMR to be dimethylbicyclo [2,2,l]-hepta diene-2,3-dicarboxylate ) was obtained.
*H NMR data : Solvent acetone - d6
5 2.2 5 2.1
5 3.7
8 6.9
5 3.85
35 Preparation of dimerhvl tetra-cvclor 2.2.1.0^.0 H]
heptane-2.3-dicarboxylate45
^rCOOCH3 hx> COOCH COOC H3 COOCH3
(14) (15)
Freshly prepared norbornadiene dimethylester (14) weighing 100 g ( 0.48 mol ) was dissolved in 1000 ml ethyl ether. The solution was placed in a 1-liter Pyrex photochemical reaction vessel ( see Figure 3 ) and stirred with a magnetic stir bar. Then
Hanovia this solution was irradiated using the 450 Watt high pressure mercury vapor lamp. The lamp was located in a quartz immersion well. The quartz immersion well
Pyrex was placed in the 1 -liter photochemical reaction vessel and cooled with water flowing around the jacket surrounding the lamp. The reaction vessel was equipped with a reflux condenser. The whole photochemical reaction vessel was covered with aluminum foil, and a N2 atmosphere was maintained during the entire reaction. The
reaction mixture was irradiated for 4.5 hours. Then evaporation of the solvent gave a
45 A. D. G. and J. A. McCulloch, A. W., Mclnnes, G., Smith, Walter, , Can. J. Chem. 1976, 54,
2013.
36 pale yellow oil. The *H NMR spectrum indicated that unreacted starting material as the only significant product. No successful results were obtained, even if the reaction time was increased from 4.5 hours to 8 hours, 24 hours, 48 hours or 72 hours. The amount of norbornadiene-dimethylester (14) was decreased from 100 g ( 0.48 mol ) to 50 g
( 0.24 mol ) and dissolved in 1000 ml ethyl ether and irradiated again for each of 8 hours, 24 hours and 48 hours. The !H NMR spectrum again indicated only unreacted
starting material.
37 Figure 3.: 1-liter Pyrex photochemical reaction apparatus:46
TO POWER SUPPLY
WATER
WATER
GROUND GLASS JOINT
SOLVENT LINE-
PYREX REACTION FLASK HIGH PRESSURE_ MERCURY
QUARTZ IMMERSION WELL
SOLVENT AND SUBSTRATE
STIRRING BAR
46Kevin Gillman, M.S. Thesis, Rochester Institute of Technology, 1991.
38 Preparation of Bicvclor2.2.11hepta-2.5-Dicarhoxvlic Acid474 8
COOH
OOH
(~ Freshly prepared cyclopentadiene 50 ml ) was slowly added to 50.0 g
( 0.44 mol ) of acetylene dicarboxylic acid which had been dissolved in 200 ml of anhydrous ether and cooled in an ice bath. The solution was vigorously stirred for four hours and the ice bath was allowed to reach the room temperature. The solution was
then heated for ten minutes on a steam bath and then cooled in an ice bath . After 30 minutes of stirring, a precipitate formed, and the mixture was stirred for another hour.
The solid was collected by filtration and more precipitate was obtained by evaporation of about one half of the ether layer. The combined solids were then dissolved in hot water, treated with charcoal, filtered, and allowed to crystallize ( in refrigerator ) overnight. After filtration, the resulting solid was dried in a desiccator for 3 days. In this way 47.30 g ( 59.7 % ) of norbornadiene dicarboxylic acid (16) was obtained of melting point : 165 - 167C
47 Organic Synthesis, collective vol. II, P 10.
48 Greenwald, B., M.S. Thesis, Rochester Institute of Technology, 1971.
39 H^.M.R data : Solvent, acetone - d6
5 2.2 5 2.3
5 5.7
OH 5 7.0 OH / 5 4.15
40 Preparation of tetracvclor2.2.1.Q2A0 Ml
heptane-2.3-Dicarhoxylic Acid
( 16 ) (17)
Pyrex The same 1-liter photochemical reaction vessel was used in this experiment. First 45.52 g of dried norbornadiene dicarboxylic acid was dissolved in
1000ml ethyl ether. The solution was irradiated for 10 hours using the 450 Watt
Hanovia high pressure mercury vapor lamp, while being stirred under an N2 atmosphere. Evaporation of the solvent gave a tight yellow precipitate. The precipitate was recrystallized from anhydrous acetone. At the end of this period, 35.69 g
(78.41%) of quadricyclene dicarboxylic acid (17) was obtained.
The product gave the characteristic complex melting behavior ( similar to that recorded49); at 235C it began to melt, at 240C it began to foam and turned brown, at
255C it stopped foaming and a brown powder was left which did not melt until
280C.
*H NMR. data : Solvent DMSO - de,
m - 5 1.9 to 5 2.8 integrates for 8H
49 Cristol, S. J. and Snell, R. L. J. Am. Chem. Soc. 1958, 80, 1975.
41 HvdrohoraHon-oxidation of Quadricyclene Dicarboxylic Acid with
BHvTHF Promoted hv Wilkinson's Catalyst
The setup, nitrogen, and all glassware went through the same procedures as described in experiment 1.
The 250 ml flask was charged with 20 ml of methanol and 1.80 g (10 mmol ) quadricyclene dicarboxylic acid was added under a stream of nitrogen, then 15 ml ( 15 mmol ) of BH3THF and 0.02 g ( ~ 0.2% mol ) Wilkinson's catalyst was added to the reaction flask. The reaction mixture was stirred at the room temperature for 24 hour, cooled in an ice bath, and then 10 ml of 95% ethanol and 10 ml of a 30% H2Q2
solution followed by 10 ml of 3M NaOH were added to the flask. The reaction mixture was stirred for 24 hours with cooling and the reagents was allowed to reach room temperature.
At the end of this experiment, a light yellow precipate ( 0.56 g ) was obtained.
This precipate did not dissolve in THF, methanol, and DMSO and thus could not be analyzed.
42 Results and Discussion
Hydroboration of Stvrene with BH^THF
As already mentioned in the introduction, unlike other terminal olefins such as
1- 1- butene, and pentene, hydroboration of styrene with sodium borohydride and boron trifluoride etherate in diglyme gave only 80% addition of the boron to the terminal carbon position, and 20% to the secondary carbon50. Similar results have been observed in our lab when we used BH3THF as a hydroboration reagent instead of
sodium borohydride and boron trifluoride etherate (B2H6). Our results were 80.7%
addition of the boron to the terminal position and 19.3% to the secondary carbon. Thus electronic effects play an important role in influencing the direction of addition of the
boron-hydrogen moiety to the carbon-carbon double bond.
All available evidence indicates that the addition of the boron-hydrogen moiety to olefins involves a four-centered transition state51. The boron-hydrogen bond in hydroboration agent is presumably polarized, with the hydrogen having some hydridic character. In styrene, as a result of conjugation, the required unshared pair of electrons can be brought to the terminal carbon atom by means of the polarization shown in structure 18 52,
50 Brown, H. C. and Zweifel, G. /. Am. Chem, Soc. 1960, 82, 4708.
51 Brown, H. C. and Zweifel, G., /. Am. Chem, Soc. 1961, 83, 2544.
W.," Chemistry" 52 Wheland, G. Resonance in organic John Wiley & sons, Inc., NY 1955.
43 NV CH=^CH2
1 ' H----B//
5- (18) 5+
As a result, electronic shifts can be applied to explain the preferred addition of the boron atom to the terminal position. Steric effects also contribute to this anti-
Markovnikov addition.
It is known that the phenyl group can also stabilize a negative charge in the a - position, and thus electrons can also be brought to the cc-carbon atom by means of the polarization shown in structure (19). This is the reason for the enhanced addition of boron atom at oc-carbon position.
CH, 'B~H. / >
(19)
- This mechanism would place the boron at the a position. The transition state
electron- such as and would be stabilized by an withdrawing substituent, p-chloro-,
such asp-methoxy- made less stable by an electron supplying substituent, group.
The first (18) of these two polarizations is apparently more important and this is why
the to the terminal position. the reaction gives more addition of boron
44 Hydroboration of Stvrene with Catecholborane
The hydroboration of styrene using catecholborane at room temperature over 1 hour gave 73.7% addition of the boron to the terminal position and 26.3% addition of the boron to the secondary carbon. Only 3.8% of styrene was consumed. Thus anti-
Markovnikov addition still dominates the addition. These results are reasonable because, as mentioned in the introduction section, electron donation from the adjacent oxygen makes catecholborane a much weaker Lewis acid. This means that catecholborane is a much weaker hydroboration agent than borane agent. As a result, the hydroboration with catecholborane is very slow at room temperature.
Hydroboration of Stvrene promoted by
Wilkinson's Catalyst
hydroboration53 Mannig and Noth first reported Wilkinson's reagent catalyzed and thus a new facet of hydroboration was revealed. We have used the Wilkinson's catalyst to promote hydroboration of styrene using catecholborane and BH3THF . Our
with catechoborane and results showed predominant Markovnikov selectivity increased
the presence of catalyst. In the Markovnikov selectivity with BH3THF in Wilkinson's
reagents afforded the anti-Markovnikov absence of Wilkinson's catalyst, however both
predominant products. The results are summarized in Table 3.
Int. Ed. Engl. 878. 53 Mannig D.; Noth H., Angew. Chem., 1985, 24,
45 Table 3 Hydroboration of Stvrene promoted with
Wilkinson's Catalyst
Reagent Catalyst % Anti-Ma % Mb % Yield Time
CBC No 73.7 % 26.3% 3.8% 1 h
CB Yesd 14.2% 85.8% 71.5% 1 h
CB Yes 3.1% 96.9 % 59.1 % 0.5 h
BH3THF No 80.7% 19.3% 78.9% 1 h
67.1% BH3THF Yes 65.9%) 34.1% 1 h
a. % of Anti-Markovnikov product (C6H5CH2CH2OH)
b. % of Markovnikov product (C6H5CH2OHCH3)
c. CB means catecholborane
d. 0.2% mol of Wilkinson's catalyst was used.
In Hayashi 's paper54, they claimed that high regioselectivity ( Markovnikov
with rhodium complexes that have phosphine addition ) was only observed tertiary ligands and a positive charge on the rhodium atom. For example they found that the
25 hydroboration reaction of styrene with catecholborane in THF at C for 30 mins in
catalyst prepared in situ Rh the presence of 1% mol of rhodium by mixing [ (COD)2]
-bis(diphenylphosphino)butane followed oxidation gave 99% BF4 and 1,4 (dppb) by
and /. Am. Chem. Soc. 54 Haysshi, T., Matsumoto, Y. Ito Y. , 1989, 111, 3426-3428.
46 of ct-phenylethanol regiospecifically (C6H5CHOHCH3 / C6H5CH2CH2OH ~ 99/ 1).
In this case, Markovnikov addition product was the major product. But when
Wilkinson's catalyst was used, the anti - Markovnikov product was the major product.
According to their results, hydroboration of styrene with catecholborane in the presence of 1 mol % of Wilkinson's catalyst gave the following ratio: C6H5CHOHCH3 /
C6H5CH2CH2OH = 10 / 90. The yield was 79%.
Evans' David A. research group55 have studied the hydroboration of styrene
with deuteriocatecholborane promoted by Wilkinson's catalyst. They observed that the
reaction of excess olefin with deuteriocatecholborane under standared conditions
afforded only one deuterium-containing product, 1 -phenyl-:deuterioethanol (100%,
C6H5CHOHCH2D).
Evans' Our reactions and observations were more similar to observations.
Hydroboration of styrene with catecholborane in the presence of 0.2 mol % of
Wilkinson's catalyst at room temperature for half an hour provided 96% of a-phenyl
ethanol Markovnikov product. Also from our results, it seems that in the presence of
Wilkinson's catalyst with less reaction time, more Markovnikov product
( C6H5CHOHCH3 ) was formed. Hydroboration of styrene with catecholborane for
one hour gave 85.8% of Markovnikov product, whereas hydroboration of styrene with catecholborane for half an hour gave 96.9% of Markovnikov product. Even though the
mechanism of hydroboration of styrene with catecholborane without Wilkinson's
catalyst offerded the anti - Markovnikov product as major product, this process
( without Wilkinson's catalyst ) is much slower than the catalytic process ( with
Wilkinson's reagent ), and the result of these two competing processes was largely
Markovnikov addition product.
55 Evans D. A. and Fu, G. C., /. Org. Chem. 1990, 55, 2280-2282.
47 We also hydroborated styrene with BH3THF in the presence of Wilkinson's catalyst. Compared to catecholborane, BH3THF is a much stronger hydroboration reagent. Our results indicated that without Wilkinson's catalyst, borane ( BH3THF ) reagent can hydroborate styrene rapidly and provide mainly anti-Markovnikov addition product. When we applied Wilkinson's catalyst to the hydroboration of styrene with
BH3THF, we found that more Markovnikov addition product was obtained. It should be noted that unlike the hydroboration with catecholborane, the hydroboration using BH3THF gave anti-Markovnikov addition as major product both with and without Wilkinson's catalyst.
The effect of using Wilkinson's catalyst was an increased percentage of
Markovnikov addition. These facts suggested that hydroboration of styrene controlled by the catalytic mechanism provides Markovnikov addition product, whereas conventional hydroboration mechanism (without Wilkinson's catalyst) provides anti-
Markovnikov addition product.
The difference between using BH3THF and catecholborane can be explained by the hydroboration rate. Since BH3THF is a much more reactive agent than
rate of hydroboration of styrene BH3THF through the catecholborane , the using conventional mechanism (without Wilkinson's catalyst) is apparently faster than the rate by the catalytic mechanism. This is why the anti-Markovnikov addition products were major products even when Wilkinson's catalyst was used. However, the catalyzed
process was fast enough to cause an increased percentage of Markovnikov addition
product to be obtained. On the other hand, the hydroboration using catecholborane without Wilkinson's catalyst is very slow as demonstrated by only a 3.8% conversion
catalyst was the of styrene. Thus when Wilkinson's used, catalytic process heavily dominated the hydroboration reaction and gave Markovnikov addition product as major
48 product. The very slow hydroboration process through the conventional hydroboration mechanism may still be present and this could give mainly anti-Markovnikov product.
The percentage of anti-Markovnikov product increased with reaction time as shown in
Table 3. This suggests that the rate of the non-catalytic process becomes more significant compared to the catalytic process as the reaction proceeds. For better understanding, let us look the proposed mechanism of the hydroboration catalyzed by
Wilkinson's catalyst.
Mechanism of Rhodium Catalyzed Hydroboration of Olefins
Noth56 Mannig and have suggested a mechanism for catalyzed hydroboration of olefins, which is analogous to that proposed for the much more thoroughly investigated rhodium - catalyzed hydrometalation reactions such as hydrogenation, hydrosilation and hydroformylation57. The mechanism is illustrated as in Figure 4:
56 Mannig, D., and Noth, H., Angew. Chem. Int. Ed. Engl., 1985, 10, 878.
57 Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G., Principles and Applications of
Organotransition Metal Chemistry ; University Science Books : Mill Valley, CA 1987.
49 Figure 4: Proposed Reaction Mechanism for a Wilkinson's Reagent
Catalyzed Hydroboration Reaction
RhL3Cl
reductive -L
elimination
RhL2Cl
H
> ( \-Rh rV,( B-Rh VL \()/ V | | VL CI CI
L = PPh3 olefin hydride binding migration
(alkene insertion)
According to the above mechanism, only the regiospecific incorporation of
deuterium at C2 of the product alcohol should be expected. After isotope labeling
studies carried out on the rhodium catalyzed olefin hydroboration reaction by Evans and
of Fu55, it was found that the mechanism these reactions is not as straightforward as
Figure 4 above suggested. When they used Wilkinson's catalyst to catalyze
- hydroboration of 1 decene with deuteriocatecholborane ( 2 mol % catalyst, THF,
50 20C) followed by oxidation, they did not find simple regiospecific incorporation of deuterium at C-2 of the isolated 1-decanol as the mechanism in Figure 4 suggests.
Instead, a significant proportion of the deuterium in the product alcohol was found at the hydroxyl-bearing carbon. But when they used Wilkinson's catalyst to catalyze the hydroboration of styrene with deuteriocatecholborane, they found deuterium corporation exclusively in the terminal carbon position of the Markovnikov product.
These results indicated that the mechanisms of the hydroborations of the 1-decene and
styrene are not completely the same. The different hydroboration results are rationalized
in Figure 5.
In the case of 1-decene, the regioselectivity determining step is reductive
ehmination step. To explain the incorporation of deuterium at C-l, the hydride
reversible step. In the case of the migration step should be considered to be a styrene,
an irreversible hydride migration step. Since these regioselectivity determining step is
and different two reactions have different regioselectivity deterrnining steps
different results. reversibility, the labeling study showed
51 Figure 5: Regioselectivity Determining Step of Styrene and 1-Decene in the Mechanism of Hydroboration Promoted by Wilkinson's Catalyst
(RO)2B-H
Rh(PPh3)3Cl
<*^n Oct
.n-Oct Ph y I (RO)2B-Rh (RO)2BRh / H/ H I regioselectivity- determining step !
Ph H H 'n-Oct (RO)2B -Rh
(RO)2B-Rh
regioselectivity- determining step
H Ph
H -Oct (RO)2B
(RO)2-B
Recently, Zhang et al. also proposed the mechanism of hydroboration for styrene promoted by Wilkinson's catalyst. It is shown in the Figure
6. In this proposed mechanism, the insersion of an olefin to M-H bond or (M-Bbond)
52 mechanism, the insersion of an olefin to M-H bond or (M-Bbond) may occur in two different ways: primary insertion and secondary insertion.
Our observations led us to believe that the secondary insertion ( to form the secondary system, ArCH(CH3)MB was the predominant step, since hydroboration- oxidation of styrene with catecholborane promoted by Wilkinson's catalyst ( for half an
hour ), gave 96.9% Markovnikov product and only 3.1% anti-Markovnikov product.
The domination of the insertion on the secondary carbon can be explained by the
formation of tj3- benzyl complex as illustrated in Figure 7.
53 Figure 6: Proposed Mechanism for Hydroboration of Styrene Promoted by Wilkinson's Catalyst:
ArCH-CH ArCH=CH22 ArLH-CH2 , CB ArCH=CH2 ArCH=CH2
M
ArCH2CH2 ArCHCH3^ ArCHCH3 ArCH2CH2 I I B M B M B B
secondary insertion primary insertion
54 rj3 Figure 7 - Benzylrhodium Intermediate
Ph3P B^ \ / Rh
Ph3P CI
K^Pnh
T|3 - The enhanced stability of benzyl complex makes the secondary
T|3 - insertion a preferred step . Such complexs have been reported. This mechanism explains why the hydroboration of styrene mainly gave the Markovnikov addition product as observed in our experiments.
Hydroboration of 2.3 - Dihvdrofuran Promoted
bv Wilkinson's Catalyst
The main purpose of this part of the project is to study the effect of Wilkinson's catalyst on hydroboration of heterocyclic olefins in an attempt to find the optimum
conditions for these systems.
In 1985, Brown's research group studied the hydroboration of 2,3 - dihydrofuran with BH3-SMe2. They found that the hydroboration of 2,3 - dihydrofuran with BH3-SMe2 ( 3: 1 molar ratio ) at 0C for 2 hours proceeded to give a
Oxidation afforded a mixture of 3- mixture of trialkylborane and borinate ( 14 ).
1,3- 1,4- hydroxytetrahydrofuran ( 10, 88% ) 3-buten-l-ol ( 11, 4% ) and and
of can butanediols ( 12 and 13, 6% ) . The formation these products be rationalized in
55 the following Figure 8 ( the mechanism has been outlined on p. 13 of the introduction section ):
Figure 8 : Hydroboration-oxidation of 2,3-dihydrofurane
+ CHi=CHCH2CH2OH
11
H202 NaOH
^oA^ BH, THF
2h
H202 NaOH
HOCH2CH2CHCH3 12 +
HOCH2CH2CH2CH2OH
13
56 We applied Wilkinson's catalyst to 2,3-dihydrofuran and the results are summarized in Table 2 and Table 3 of the experimental section.
These results indicate that Wilkinson's catalyst caused different effects when the ratio of reactant to hydroboration reagent was changed from 3:1 to 1:1. When the ratio of 2,3-dihydrofuran to BH3THF was 3:1, the ratio of main product ( 3- hydroxytetrahydrofuran, 10 ) in the product mixture was 73.4% in the absence of the
Wilkinson's catalyst. In the presence of Wilkinson's catalyst, the ratio was 81.5%.
However, when the ratio of 2,3-dihydrofuran to BH3THF was changed from 3:1 to
1:1, the ratio of 3-hydroxytetrahydrofuran in the product mixture was 55.0% in the absence of Wilkinson's catalyst. It was changed to 50.0% in the presence of
Wilkinson's catalyst. Since the mechanism of hydroboration-oxidation of heterocyclic olefins is not yet known, we are still unable to explain these results.
The product yield was lower with Wilkinson's catalyst than without
Wilkinson's catalyst. The possible reason for this may be the following: since 2,3 - dihydrofuran has an electron rich oxygen and Wilkinson's catalyst has a vacant site, the electron rich oxygen might bind to the Wilkinson's catalyst such that further reaction
other the Wilkinson's catalyst might be deactivated may be suppressed. In words, by
2,3-dihydrofuran. Further evidence is needed to test the above suggestion. Evans has
also printed out that Wilkinson's reagent is subject to oxidation which can affect the
product ratios.
These results also showed that in the presence of excess hydroboration reagent,
the total the ratio of the main product (3-hydroxytetrahydrofuran, 10 ) in product
the presence of excess hydride cause mixture was much lower. This is because ring
which to side products. cleavage of the alkylboranes, leads
57 Hydroboration of the Cyclopropane Ring in a Quadricyclene System
promoted hv Wilkinson's Catalvat
Other research workers in our group were studying Wilkinson's catalyst promoted hydroboration of a cyclopropane ring in quadricyclene. One of my research projects was to hydroborate a cyclopropane ring in quadricyclene dimethylester or
quadricyclene dicarboxylic acid. The new reaction that we plan to perform is:
1) BH3,THF or CB, WILK. Cat. -*? COOCH 3 2) H202, NaOH, H20
COOCH 3
COOCH 3
COOCH 3
OH H
as a substrate for this We prefer to use diester rather than diacid reaction,
might susceptible to because the hydroborated diacid intermediate be protonolysis by
58 the rest of the diacid58. One typical example to illustrate the above point is shown below.
RSCH 2CH= CH 2_ RSCH 2CH2CH2 Jg2^RSCH 2CH 2CH3
/B\
Therefore, we may not be able to use the diacid for the hydroboration experiment because the following reaction may happen.
COOH
COOH Ao/ \
We first attempted to prepare the quadricyclene dimethylester as the starting material for the hydroboration reaction. In principle, the synthesis can be achieved through the (2+2) addition of norbornadiene dimethylester.
Norbornadiene dimethylester was successfully prepared by reaction of
Diels- cyclopentadiene with dimethyl acetylenedicarboxylate. The Alder addition (2+4) of two reactants gave us norbornadiene dimethylester. The product was verified by
200 MHz *H NMR spectra.
58 Pure and Appl. Brown , H. C.and Singaram, B., Chem., 1978, 59, 879.
59 Norbornadiene dimethylester synthesized in the previous experiment was placed
Pyrex in 1 -liter photochemical reaction apparatus and irradiated for 4.5 hours. The
*H NMR spetra indicated that the expected (2+2) addition had not happened. To study whether the reaction time had an effect on the addition, we performed our experiments with the different irradiation time ranging from 4.5 hours to 8 hours, 24 hours, 48 hours and 72 hours. The *H NMR analysis still indicated that the (2+2) addition product was not present in the mixture. We also experimented with different (more dilute) concentrations of norboranadiene dimethylester to avoid polymer formation.
The amount of starting norbornadiene dimethylester decreased from 100 g (0.48 M) to
50 g (0.24 M), and then the solution was irradiated for 8 hours, 24 hours and 48 hours respectively. An analysis of the product mixture using 200 MHz *H NMR still
showed none of the desired 2+2 addition product.
The above results suggested that we may not be able to use norbornadiene dimethylester directly to synthesize quadricyclene dimethylester. One possible reason is
that norbornadiene dimethylester may form polymer under irradiation, although the
concentration study did not show this.
Because of the difficulty in synthesizing quadricyclene dimethylester from
norbornadiene dimethylester, we decided to use quadricyclene dicarboxylic acid for the
hydroboration study despite the possible problem mentioned above.
norbornadiene dicarboxylic acid a 2+4 First, we successfully prepared by
Diels-Alder addition of cyclopentadiene and acetylene dicarboxylic acid. The product
was verified by !H NMR spectrum.
Norbornadiene dicarboxylic acid prepared in the above experiment was
irradiated for 10 hours. The reaction product was analyzed by *H NMR. The *H
NMR indicated that there was no norbornadiene dicarboxylic acid present. The olefin
60 proton signal at 8 7.0 had disappeared which proved only quadricyclene dicarboxylic
acid was present.
Hydroboration-oxidation of Quadricyclene diearhoxvlic acid with
BH3 THF promoted by Wilkinson's catalyst
The precipitate from reaction mixture could not dissolve in THF, methanol, and
DMSO. Good reaction and workup procedures are needed for the study
Furture work : first someone can hydroborate quadricyclene dicarboxylic acid
directly using hydroboration reagent BH3THF ,catecholborane or other reagents to
study the hydroboration of cyclopropane ring with and without the presence of
Wilkinson's catalyst. Secondly, we can synthesize quadricyclene dimethylester from
quadricyclene dicarboxylic acid and then hydroborate quadricyclene dimethylester.
61 00- u m L ^ w 62 l\> aa S RS -CCM^. -M bocoicn ova w a. ru l* 3 O (M ^ IP IT o "* o&ou A a C\ t o Gicnotn-c/:x &B 63 aa l*- OO O&ruX C eotooottto O) -* * ni- e am | O K OtClCM ooboic* oca Pff.lN W -" . i oirmr.fn W ff Ory 'itDo ry -r^irjin ft ryJ t*D*f, *riTlTW op 1010 ? oac-iu r. t- ^L vi 5* o Rnon*-cnz Esax- Cos j3uuku.ZD.vi \3 ZTTT 8 64 GC - Mass spectrum of the reaction of styrene and BH3THF without Wilkinson's catalyst Scan BB (1 .674 nm) Of ORTR:PINS 0 2. BETS- c / 107 u 79 c 1. SCS-5 tt 3 31 122 ' a 1 ers^ 16 c es / BB \ j 3. BC4- / a \ a .,tl, ! ., lmJ , ,1. B Jill. U . , , .1.1 2B 4B ED BB IBB 12B Matt ,'Ch arga TI C Of ORTF): FINC.D 3. BC7- I 2.BE7- C 1. BE7 : X1 ll * B^ \ , Tim Cn 1 n . 1 Scan 71 (1 . 7B2 bd j n 3 of DRTfi: PIN 3.0 at \ 1. SEE "i a 91 c It BEB- 1 . 122 B 19 B3 C / 77 X 5. 31 BE3: ie / a / a. J B J.... "'1 ' 1. 2B 4B EQ BB IBB 1B Matt Charp TIC of ORTR:PINC.O 3.BE7- u c 2 BE7- C i.BE7: 0 A __ 1 1 13 T (ii. 1 Mn oTofb:Pii;.& Peakl Ret Tiee Type Width Area Start Tine End Tine 1 1.276 PV O.We 1B1R4831B4 1.1S2 l.4?5 2 1.462 W 6.076 15321058 1.425 1.M8 3 1.676 W 0.D35 2339S&73 . 1.631 1.732 4 1.783 *B G.W7 97?386>7 MY 1.732 1.914 65 GC - Mass spectrum of the reaction of styrene and BH3THF with Wilkinson's catalyst Scan 71 C1.77B nm) of DfiTR:5TrRENE2.D l-3EB: ^ 1B7 ~~^ u 3 ; 9 c BEt- 13 1. / 122 "B 39 C if S. BE3: XI E3 . CC ' ' , ,1. a .....I II. i.ili II 2B 4B EB BB IBB 12B Mi8t/Chrgi TIC of DRTR: STVRENE2. O t or 7 o c * 2.BE7: a c l.BE/ *! a CC B LLJUi, Tin Coin.) Scan 7? U.9B2 mm) of DRTR: 5TVRENE2 . 0 rt 9 S3 C 31 / X> 13 CC I I | -* 4L Ma. H'Nl) B 4B BB EB IBB 1B rm /Chap; e TIC of DRTR:STVREME2.D g. Br7- u c 2. A be?: TJ C l.BE/: JO ec B: Tin* (inn.) Pe&kt Ret Tine Type Width Area Start TiM End Tiee t 1.294 VH 6.fi88 17nS51?fl?1 i.rno 1.480 2 1.514 VH 6.053 8D3UQf3 1.190 1.668 3 1.771 VH 6.635 173323161 1.726 1.843 4 1.996 PV 6.638 345196495 1.848 2.149 c 3.556 W 6.634 3736291 3.512 3.61R 66 Bean 9* CI. 9*7 ttm) af OUT*.: PINCCB. D 4.BCB- u " c l.BEE- 3 a i.bes- - c S X IBS .g .__ 5 a i.bcb- \ I J / IBS i - '5 N 1 j. J '\ / ta 4a aa bb ibb ibb it e IBB TIC I tf OP.TP.: PINCCB. O | 1.BE7 1.SC7 1 1 t.ut? 1 I o I a. act f^wj . t CA Bean TB CI. BBS rm) of OP.TP,: PINCCB. O . "5 s \ IB? S.BC4- f} c CQ o s "2.BE4- C B4B 1 2 ji..yI'Y f . l. r 1 SB IBB 198 BBB i H>ll /CMrtl la o TIC Bf ORTHi PINCCB. 0 E 2 I.BE7 u I ? c I.9E7 at a i o 00 c I.BE7 3 a 9.8E6 tt 1 1 B 1 4 Ti *ii Cat 1 n. > u o Bean BE (S.SB9 aiinl of OP.TP.: PINCCB. O t.BES* i 1 i - I.9CS' I.BES- BBB 9.BE4- T '/"/'a. i \v 7 . 1 \ SB IBB I9B BBB Maaa/Charaa i. TIC Of OP.T P.! PINCCB. D t t.BCr t i t.azr 1 - i t.ac? I 9.BEB ^JL 1 i> k 4 - 19 9 i Tla Coin.) P**k Rat Tim Ar" St.rt Tiw 1W ' End Tiaia i i:i.i W 1:83 .\mili\ \:\n 9 1.983 W 0.060 6060061 1.907 2.135 4 2.197 5'S5 22614697- fy. 2.135 2.26V 5 2.471 W 0.044 46820719$ 2.321 2.6BE( 67 GC - Mass spectrum of the reaction of styrene and catecholborane with Wilkinson's catalyst (reaction time 0.5 hr.) Scan B2 C1.B64 nm) of DRTR: PXNGC82. 0 1.3EB- y ^ i 79 1B7 l.BEB- 43 SI 122 3.BE3- 27 i \ 91 BJ M. ...i 1 Jill _~l , J. 4B EB BB IBB 12B Miti/Chargi TIC Of DRTR: PINCCB2. D 2. BE7 1. 3E7 1.BE7 3. BEE B 2 a 4 Ti w>m (ill n. J Scan 9B C2.B26 ntn) of CRTR: PINGCB2. 0 y\ u 1.BE31 91 c 122 5.BE41 28 / c 131 a 1B3 o / il ! I .' 1 * 1 B iUt.,..Ji il >> i. 1 1 4B EB BB IBB 12B MB IBB TIC Of DRTR: P1NCCB2. D 2. BE7: 1.SE7-; 1 . BE7 3.BEB- B I 1 -4 * S Ti na ttii n. > Peak* Ret Time Type Width Area Start Time End Time 1 1.252 UH 0.070 1089329085 1.155 1.481 2 1.509 UH 0.026 6609628 1.481 1.520 3 1.553 PB 0.042 236675122 . 1.520 1.740 * 4 1.860 BU 0.042 189123895 1.769 1.965 **.% 5 2.023 uu 0.039 9734965 1.965 2.095 6 2.162 PU 0.043 173367086 2.095 2.368 68 GC - Mass spectrum of the reaction of 2,3-dihydrofuran and BH3THF without Wilkinson's catalyst . Baiatn 7B (a .BOB mlma mt ORTS.PIMQ.O 4.BEB" u >o ^1 |29 37 c 3.BEB- m 2.BEB" c a 7B BB 93 142 0 ' CC < y ,..|| Ii. ..Lull, 4B BB BB 1BC 1EB 14B Mitt/Chirst TIC of DRTR: PING. 0 3.BE7- 1 ' ti c 2.BE7: m a c a 1.BE7- CC nj J 2 4 B Tt na (nin. ) Scan 91 CI 721 mini of DRTRsPING.O B.BEB-j ^ a 'i 1 A 2 c 4.BEB- M -B . 37 71 C 1B1 a 2.BEB-; | / / a. 117 0 / / CC .ll 1 nil 1 4B BB BB IBB 12B MasB/Charoa rTIC Of DRTR:PING.D 3.BE7- c u ' c * 2.BE7"; ' -B C , a 1.BE7- X CC K 2 4 B T1 na Cm n. ) Peekt Ret Tiae Type Width Area Start Tiae End Tiae 1 1.265 PV 6.683 357958165 1.126 1.463 Z 1.533 W 6.653 896524266 1.463 1.655 3 1.718 W 8.666 682618936 1.655 1.919 4 2.619 BY 6.834 7288137 2.758 2.838 5 2.857 W 8.636 7683686 2.838 2.904 6 2.965 W 8.629 3516984 2.931 3.664 7 3.657 PV 6.838 2649J732> 3.664 3.186 8 3.269 W 6.824 19673863 3.233 3.313 9 3.351 w__ 8.63$ 34217593 3.313 3.426 69 - GC Mass spectrum of the reaction of 23-dihydrofuran and BH3THF with Wilkinson's catalyst Bean 77 CI. 302 mn) of DRTR : PXNC.O 2.5EBJ u * 4 9 ! 7 c 2. BEEj 43 B 1.5EBJ 32 C 1. \ 4/ a / |/ S3 61 7B ?3 BB s> / CC S.BE51 L ...l.llll. \ ../ li 1 [ / 1 SB 4B SB BB 7B BB 9B Matt /Charoa ;XC of DRTR: PING. D 1.3E7 u c * 1.BE7 C \\ a 0 3. BEB CC 1 B 1 2 3 4 3 Ti na Cm n. ) Scan 63 (1.62B mn) of ORTR:PING.D 44 2.3cm 2. BE3J 1. 3E3i 71 1. BE3l 77 91 134 3. BE4~i y y i. ""*9r"""""l""""""f in ii ! in.' ''xi..iii1 1. 1 1, . . B *m 'i '"I 4B EB BB IBB 12B 14B Mas* /ChirQi Peak! Ret Tiae Type Width free Start Tiae End Tiae 1 1.192 PH 8.622 2561289 1.167 1.214 2 1.241 PV 6.666 878855121 1.214 1.438 3 1.451 W 8.624 2274285 1.438 1.464 4 1.563 w 8.629 .286194343 1.464 1.582 5 1.629 w 6.831 < 26211559 1.582 1.769 6 1.852 w 6.621 3838661 1.789 1.897 7 2.452 w 8.644 4699129 2.418 2.486 8 2.517 w 6.642 1498$248i 2.486 2.617 9 2.806 BY 6.623 .22224535J 2.735 2.847 70 1 * 26928' ' 986* dd 9*C1 2SCS s i we* 5ua f^W'CC 8d 2869t2 ^8^** 62220* tee* I Ad ecu S2' E98* ei6e2*99 8d .111192* Zft XW38W Hxam 3dAi WSdW 1 rA X?3*V L J -- v^ 12ICCICI 1661 MC nnr fit #Hna dOlS f a 2SCS 5 E t.*l'* u o a ?62** 82^*e 71 Capillary GC spectrum of authentic P - phenylethanol sample H OH r\-c- c-h \=/ 1 H A 3.783 4.428 4.797 5.884 5.438 1344I34 JUL 31. auHt 44 AREA* AREA* TYPE 610THIOTH T AREA 3.4742 6 .662 3. 763 4469314 .61316 6 .669 4.426 1547 .62616 66 .672 4.767 2466 36.47742 6 .674 9.664 3717666 .66161 164 6P .667 9.456 72 apillary GC spectrum of the reaction of styrene and catacholborane with Wilkinson's catalyst (reaction time 1 hr. ) 3.781 _j 3.881 4.776 5.362 STOP RUNt 47 JUL 31. 1991 141 13142 AREA* RT AREA TYPE WIDTH AREA*: 95.36314 3.761 8586675 BV .662 3.661 125131 VV .645 1.48299 4.167 46929 VV .667 .45883 4.228 23478 VV .657 .28562 4.422 2785 VP .673 .63832 PB .672 1.63218 . 4.776 145568 BB .676 .26918 .5.675 24812 ee .684 .55786 .5.362 49763 73 GC spectrum Capillary of the reaction of stvrene and catacholborane with Wilkinson's catalyst (reaction time 0.5 hr. ) 3.784 ><- 234 4.788 3.876 > 366 STOP UNI 48 JUL 31. 1991 14I2H53 tlX RT AREA TYPE yiDTH AREA* 96.39917 1.784 3916826 PB .665 1.22791 4.234 73367 PP .671 1.67959 4.766 113366 VB .869 1.678 3696 6P .674 .86348 6.666 26364 PB .685 .42986 74