Boranes in Organic Chemistry 2. Β-Aminoalkyl- and Β-Sulfanylalkylboranes in Organic Synthesis V.M

Eurasian ChemTech Journal 4 (2002) 153-167

Boranes in Organic Chemistry 2. β-Aminoalkyl- and β-sulfanylalkylboranes in organic synthesis V.M. Dembitsky1, G.A. Tolstikov2*, M. Srebnik1 1Department of Pharmaceutical Chemistry and Natural Products, School of Pharmacy, P.O. Box 12065, The Hebrew University of Jerusalem, Jerusalem 91120, Israel 2Novosibirsk Institute of Organic Chemistry SB RAS, 9, Lavrentieva Ave., Novosibirsk, 630090, Russia

Abstract Problems on using of β-aminoalkyl- and β-sulfanylalkylboranes in organic synthesis are considered in this review. The synthesis of boron containing α-aminoacids by Curtius rearrangement draws attention. The use of β-aminoalkylboranes available by enamine hydroboration are described. Examples of enamine desamination with the formation of alkenes, aminoalcohols and their transfor- mations into allylic alcohol are presented. These conversions have been carried out on steroids and nitrogen containing heterocyclic compounds. The dihydroboration of N-vinyl-carbamate and N-vinyl-urea have been described. Examples using nitrogen and oxygen containing boron derivatives for introduction of boron functions were presented. The route to borylhydrazones by hydroboration of enehydrazones was envisaged. The possibility of trialkylamine hydroboration was shown on indole alkaloids and 11-azatricyclo- [6.2.11,802,7]2,4,6,9-undecatetraene examples. The synthesis of β-sulfanyl-alkylboranes by various routes was described. The synthesis of boronic thioaminoacids was carried out by free radical thiilation of dialkyl-vinylboronates. Ethoxyacetylene has been shown smoothly added 1-ethylthioboracyclopentane. Derivatives of 1,4-thiaborinane were readily obtained by divinylboronate hydroboration. Dialkylvinylboronates react with mercaptoethanol with the formation of 1,5,2-oxathioborepane derivatives. Stereochemistry of thiavinyl esters hydroboration leading to stereoisomeric β-sulfanylalkylboranes are discussed. Examples of radical thiilation of various structural types vinylboronates were presented. In particular, 1,3,2-dioxaborinanes and 1,3,2-dioxaborolanes, containing by boron atom vinyl-, propenyl-, isopropenyl- or isopropylidene substituents have been used. Thiilation has been achieved by use of alkylmercaptanes, as well as mercaptamine derivatives. Alkylmercaptanes were able to replace the bromine substituent in tris-(2- bromoctyl)-borane. Dialkylvinylborates have been added hydrosulfite with the formation of 2-boronoethane sulfuric acids. A lot of examples of radical thiilation of vinylboronic acid dialkyl esters with mercaptoacids are presented. Under the azaisobutyric acid dinitryle conditions thioglycolic, β-mercaptopropionic, 2- mercaptoamberic acids and their esters as well as cysteine were added. Vinyl-, propenyl- and isopropenyl- dioxaborolanes were also participated in the thiilation with the formation of acetic, propionic or amberic acid thioethanoboronates. The high reactivity of B,B,B-trivinyl-N,N,N-triphenylborazine in the reaction with thiophenol, leading to B-tris-(phenylmercaptoethyl)-N-phenylborazine was shown. The problems of asymmetric hydroboration leading to chiral β-sulfanylalkylboranes were discussed briefly. In particular, an example, including dihydro-thiophene hydroboration, leading to (+)-R-thiofan-3- yl-diisopinocamphenylborane, and the interaction with acetaldehyde with the formation of (+)-R-3- thiophanyl-diethoxyborane was implemented. The reaction with 3,4-dihydrothiapyrane proceeds analo- gously. A synthetic route to sulfono-norbornen-boronic acid esters by Diels-Alder reaction of cyclopentadiene with arylsulfanyl-vinylboronic acid esters has been discussed.

Introduction groups of synthetic compounds and structurally similar groups with the corresponding structures B-C-C-

β-Aminoalkyl-and β-sulfanylalkylboranes are rare NR2 and B-C-C-SR. These compounds have been *corresponding authors. E-mail: [email protected] partially reviewed [1-6].

 2002 al-Farabi Kazakh National University 154 Boranes in Organic Chemistry (2)

β-Aminoalkylboranes (B – C – C – NR2) to give intermediate complexes which in boiling diglyme lead to 2-pentene and 3-heptene, respectively. Synthesis of boron containing analogue of amino On the other hand, if R and R1 are ethyl and butyl, for acids instance in 2-ethyl-1-N-pyrrolidyl-heptane, 2-ethyl- hexene was formed in 42% (Scheme 2), where 2 and In certain cases, β-aminoalkylboranes could be iso- 3 are β-aminoalkylboranes. lated. For example in the synthesis of boron-containing The enamines of cyclic ketones were hydroborated amino acids. Curtius rearrangement gave the β-boryl in the β-position in all cases. 1-N-piperidylcyclohexene alkyl amine, which is an analogue of aspartic acid 1 4 reacted with diborane to give trans-2-N-piperidyl- (Scheme 1) [7]. cyclohexyl-borane 5, which under acidic conditions converted to cyclohexene 6 with yields of 88-98% Hydroboration of enamines (Scheme 3) [8,9]. 4-tert-Butyl-1-N-pyrrolidylcyclohexene 7 reacted Aliphatic enamines easy react with diborane to with diborane to form an equimolar mixture of the form intermediate β-boryl alkyl amines. Thus, Lewis isomeric β-aminoorganoboranes 8 and 9 which were and Pearce [8,9] showed that pyrrolidine enamines of smoothly converted to 4-tert-butylcyclohexene 10 by 3-pentanone and 4-heptanone reacted with diborane protolysis (Scheme 4) [9].

O NaCH(COOEt)2 COOEt OH- O O COOEt B Cl O B COOEt B COOH O O

1. (C6H5O)2-PO-N3 NHZ HN(CH CH OH) O NHZ 2. Et3N O 2 2 2 H N B β COOEt B COOEt O O

1. KOH 2. H+ β COOH 3. H2 (HO)2B NH2 1 Scheme 1

B2H6 C2H5COOH NC=CHR NCHCHR RCH = CHR1

R1 R1 B 2

C H C H 2 5 B H 2 5 H+ 2 6 C2H5 NHC=C NCH2C B H9C4 C=CH2 C H C4H9 4 9 3 Scheme 2

B H6 N 2 N N RCOOH + N B2H6 RCOOH THF BH2 BH2 N H2O, to THF B H2O, to 6 10 4 5 7 8 9 Scheme 3 Scheme 4

Eurasian ChemTech Journal 4 (2002) 153-167 V.M. Dembitsky et al. 155

The hydroboration of the enamines of α-substi- 12 and oxidation leads to stereoisomeric amino tuted cyclohexanone 11 formed β-aminoalkylborane alcohols 13 and 14 (Scheme 5) [10].

N B2H6 N H C B H3C THF 3

11 [O] 12

[O]

N N + H3C OH H3C OH

1340% 14 24% Scheme 5

Alkyl-substituted amino alcohols 16 can possible to the asymmetrically substituted compound 17 via to convert symmetrically substituted cyclohexanones β-aminoalkylborane 15 (Scheme 6) [11-13].

O N N B2H6 B

N 1. [O] 1. CrO3 OH to OH O 2. H2O O 2. H2 /PtO2

16 17 Scheme 6

A keto group in an adjacent position could also be cyclic ketones via β-aminoalkylborane 18 (Scheme obtained on a series of asymmetrically substituted 7) [11,13].

O N N

H3C H3C H3C B B2H6 β

H3C OH H3C O [O]; to [O]; H2

Scheme 7

Eurasian ChemTech Journal 4 (2002) 153-167 156 Boranes in Organic Chemistry (2)

An analogous conversion has been carried out in aminoalkylborane 23 with a trans-diequatorial the steroids series. Thus, 3-N-pyrrolidyl-2-cholestene location of the substituents, which is converted to 3- 19 was converted to 2-cholestene 21 via 3-β-N- cholestene 24 by protonolysis [9]. 3-N-Pyrrolidyl-3,5- pyrrolidyl-2-α-cholestanylborane 22 [9] (Scheme 8). cholestadiene 25 was converted to 3-β-N-pyrrolidyl- Also 3-β-N-pyrrolidyl-4-cholestene 22 formed a β- 5-cholestene 27 via β-aminoalkylborane 26 [14].

B B2H6 H+ THF N N H H H 19 20 21

+ B2H6 H THF N N H H 22 B 23 24

B2H6 H+ THF N N N 25 B 26 27 Scheme 8

Hydroboration of 1-N-methyl-1,2,3,6-tetrahydro- aminoalkylborane 35 (Scheme 10) [18]. pyridine 28 gave a mixture of 1-N-methyl-3- piperidinol 31 and 1-N-methyl-4-piperidinol 32 via C H C H β γ 6 5 6 5 the corresponding -aminoalkylborane 29 and - B H3C N aminoalkylborane 30 (Scheme 9) [15-17]. H C H N N OH 6 5 BH2 OH CH H 3 CH3 35 33 34 N N Scheme 10 CH3 CH BH3 [O] 3 31 71% 29 The reaction of 4-alkyl-substituted 1-N-methyl- N BH2 OH 1,2,3,6-tetrahydropyridines 36 with diborane pro- CH3 ceeded in a similar manner [19] and gave a 50% mix- 28 ture of isomeric alcohols 39 - 41 [84]. The reaction N N undergoes via the corresponding β-aminoalkylborane

CH3 CH3 37 and γ- aminoalkylborane 38 (Scheme 11) [19,20]. 30 32 29% The hydroboration of N-carbobenzyloxy-3,4- Scheme 9 dehydro-DL-proline methyl ester 42 proceeded to give 10% trans-hydroxy-DL-proline 45 and 70% cis-hy- The hydroboration-oxidation of 1-N-methyl-4-phe- droxy-DL-proline 46 via the corresponding β-amino- nyl-1,2,3,6-tetrahydropyridine 33 provided trans-1- alkylborane derivatives 43 and 44 (Scheme 12) [21]. N-methyl-4-phenyl-3-piperidinol 35 via the β- 2,3-Dicarbomethoxy-2,3-diazabicyclo[2.2.1]hept-

Eurasian ChemTech Journal 4 (2002) 153-167 V.M. Dembitsky et al. 157

B B B2H6 β + γ N R N R N R

CH3 37 CH3 38 CH3 36

OH OH R=CH3 HO R=C2H5 R= n-C3H7 R= iso-C3H7 N R N R N R

CH3 CH3 CH3 39 40 41 Scheme 11

B COOCH B 3 COOCH3 COOCH3 H H + N N N H CBZ 43 CBZ 44 CBZ 42 OH- OH-

OH HO COOH COOH H N N H H H 45 10%46 70% Scheme 12

5-ene 47 reacted with diborane followed by oxidation Synthesis of alkenes from enamines with hydrogen peroxide in alkaline medium where β- elimination from 48 leads to 4-(N,N’-dicarbometho- β-Aminoborane intermediates 51, 52 and 54 xyhydrazo)-cyclopentene 49 (Scheme 13) [21-23]. formed isomerically pure enamines under hydrobor-

N COOCH3 COOCH N 3 N COOCH3 B2H6 [O] N B β HO N N COOCH3 47 48 COOCH3 COOCH3

OH-

COOCH3 N NCOOCH3 H+ NCOOCH3 N COOCH3 49 Scheme 13

Eurasian ChemTech Journal 4 (2002) 153-167 158 Boranes in Organic Chemistry (2) ation reactions [24]. Morpholine enamine of propio- O 1. Me2S-BH3 OB(OMe) 2 H2O2 phenone 50 reacted with dimethylsulfoboron hydride N N H 2. MeOH to give derivatives of boronic acid which could be H neutral 50 Ph Ph 51 converted to the amine oxide without affecting the OB(OMe)- boronic ester [25] and than eliminated to (E)-1-phenyl- O 2 syn elimination propene 53. If the hydroboration was carried out with +N H Ph β Ph 9-BBN, an intermediate -aminoalkylborane 54 was H 53 75% formed which β-eliminated in an anti manner to give 52 O H B OH (Z)-1-phenylpropene 55 (Scheme 14) [26,27]. B N N Synthesis of β-aminoalkylboranes from urea H 50 Ph Ph 54 derivatives anti elimination Lewis and Pearce [8] reported that when diborane Ph 55 81% in tetrahydrofuran was treated with N-cyclohex-1- MeOH enylpiperidine and the resulting organoborane hydro- Scheme 14 lyzed, there was obtained an almost quantitative yield of trans-2-N-piperidylcyclohexylboronic acid 57. corresponding β-aminoalkylboranes 60 and 61. The Similarly, Butler and Soloway [28] hydroborated N- cyclohex-1-enyl-urea 62 reacted with diborane in vinylurea 56 and realized an 80% yield of dimethyl β- tetrahydrofuran to form β-aminoalkylborane 63. Ben- ureidoethylboronate 58 after treating the intermediate zyl-vinylcarbamate 64 with diborane gave the benzyl with excess methanol (Scheme 15). Derivatives of ester of (2-dihydroxyboranyl-ethyl)-carbamic acid 65 propenylurea 59 reacted with diborane to give the [28].

H O O O N B2H6 HN NH2 β CH3OH B O THF H2NN O H B H 58 56 H 57 H H B2H6 O N O N O MeOH B O O O 56 60

H H B H O N 2 6 O N O MeOH B O O O 59 61 H H NNH2 NNH2 B2H6 O THF O B O O 62 63

O O O H B2H6 ON B MeOH ON O 64 H 65

Scheme15

Eurasian ChemTech Journal 4 (2002) 153-167 V.M. Dembitsky et al. 159

Reactions of boranediamines with ketene boration of ketene 66 with HalB(NR2)2 67 – 70 leads to β-aminoalkylboranes 71 - 74 with common struc-

Paetzold and Kosma [29,30] have studied the prod- ture [(R2N)HalB-CH2-CONR2]2 (Scheme 16). For ucts formed by aminoboration of ketene. The amino- details of this reaction see our review [31].

O NR2 R N B 2 + - + [R2N]2BX - + O B NR2 R N 66 2 X O

67. R=Me; X=CI 71. R=Me; X=CI 68. R=Et; X=CI 72. R=Et; X=CI 69. R=Me; X=I 73. R=Me; X=I 70. R+Me; X=Br 74. R=Me; X=Br Scheme 16

Synthesis of derivatized porphyrins a protected β-aminoethyl group into arenes and alkenes was reported by Kamatani and Overman [33]. It In studies of modified porphyrin complexes, β- was shown that benzyl-vinylcarbamate 64 reacted with aminoalkylborane was obtained [32]. The authors used [9,9']bi[9-bora-bicyclo[3.3.1]nonyl] 77 in tetrahydro- 4,4,5,5,4',4',5',5'-octamethyl-[2,2']bi[[1,3,2]dioxa- furan to form the benzyl ester of [2-(9-bora-bi- borolanyl] 75 for reaction with bromo Zn+2 complex cyclo[3.3.1]non-9-yl)-ethyl]carbamic acid 78 (Scheme and obtained compound 76 (Scheme 17). 18).

A Suzuki coupling method Synthesis of isonitrile-triphenylboranes

A Suzuki coupling method for direct introducing Bittner et al. [34] by the reactions of triphenyl-

O O N N B B N N Zn O O Zn 75 β N N 80 oC, 2 h, DMF N N O Br B O

76 Scheme 17

O B THF B O + N B -10-20oC, 4 hrs H HN O 64 O 77 78 Scheme 18

Eurasian ChemTech Journal 4 (2002) 153-167 160 Boranes in Organic Chemistry (2) boranes 80 with isonitriles 79 obtained 81. When phenyl-1,3-diaza-4-bora-spiro[5.5]undec-1-en-2-yl)- heated 81 was transformed to (3-cyclohexyl-4,5,5-tri- triphenylborate 82 (Scheme 19).

- + H B N R R β B(C6H5)3 R - (H5C6) - + BNR + NC (H5C6) + N 79 (H5C6) - B R=CH3 80 R=-(CH2)5 - 50% H2SO4

140oC C6H11 -NH2 10 min 81 +

(OB - C6H5)3 H + - N B β

N 82 B

Scheme 19

Synthesis of borylhydrazones to form the dimethyl ester of 2-(N’-benzylidene-N- methyl-hydrazino)-3-boranyl-succinic acid 85 (Sche- Hydroboration of enehydrazones 83 and 84 under me 20). Similarly, the dimethyl ester of 2-(N’-ben- different conditions gave a series of stable boranes zylidene-N-methylhydrazino)-but-2-enedioic acid 84 85 - 88 [35]. Thus, the dimethyl ester of 2-(N’-ben- containing different substituents in the 4-position of zylidene-N-methylhydrazino)-but-2-enedioic acid 83 phenyl, reacted with diborane to form β-aminoalkyl- reacted with diborane in bis-(2-methoxy-ethyl)ether boranes 86 – 88.

O HH B O B H (E) 2 6 H O O N N β N N O O O O 83 85 O HH B O (E) BH3 N H O N O N N O O O O R 84

R 86.R=Br,87.R=OMe,88.R=NO2 Scheme 20

Eurasian ChemTech Journal 4 (2002) 153-167 V.M. Dembitsky et al. 161

In cases when the crotyl or acrylic acids were used ethers, were formed 89 and 90 from the corresponding for reactions with diborane bis-(2-methoxyethyl)- esters respectively (Scheme 21).

O (E) HH B H B N 2 6 N N N O O N O O 89 N O O O O HH (E) B N B2H6 N N O N O N O O 90 N O O Scheme 21

Hydroboration of trialkylamines 100 after oxidation. Intermediates were β-aminoalkylboranes 97 and 98 (Scheme 23) [15,36]. Amine groups complex strongly reacted with borane and β-hydroborate with formation of β- β-Sulfanylalkylboranes (B – C – C – SR) aminoalkylborane 92 [15,36], for instance of alkaloids 91 (Scheme 22), followed by oxidation to form two Synthesis of boryl thioamino acid alcohol isomers 93 and 94. Complexation of amine groups with borane has β-sulfanylalkylborane 101 was obtained by addi- also been found for some tetrafluoro derivatives 95 tion of cysteine to dibutyl vinylboronate (Scheme 24) and 96 providing the corresponding alcohols 99 and [37].

BH2 H3B N N β BH3

COOMe COOMe N N H 91 H 92

[O] OH OH

N N

COOMe COOMe N N H 93 H 94 Scheme 22

Eurasian ChemTech Journal 4 (2002) 153-167 162 Boranes in Organic Chemistry (2)

CH BH3 3 CH3 H3C N N F F N F

BH3 [O] F F F

BH2 OH F F F F F F 95 97 99 COOEt BH3 COOEt N EtOOC F N F N F [O] F BH3 F BH2 F OH

F F F F F F 96 98 100 Scheme 23

COOH AIBN COOH B(OBu)2 + (HO)2B HS NH2 S NH2 Scheme 24 101

Thioboration of acetylenic compounds with ethoxyacetylene 103 to form stereospecifically cis-addition product β-boryl alkyl thioether 104 in 3-Methyl-1-ethylthioboracyclopentane 102 reacted good yield (83%) (Scheme 25) [38].

H C 3 H3C 20oC SC2H5 BSC2H5 +HC COC2H5 B CC H OC2H5 102 103 104 83% Scheme 25

Synthesis of heterocyclic compounds O H2S B SBO Butyl divinylboronate 105 added to hydrogen sul- fide in the presence of azobisisobutyronitrile to form 106 12% 105 4-butoxy-1,4-thiaborinane 106. Also divinylborinic acid 2-dimethylamino-ethyl ester 107 reacted with H S 2 O B H2S to form dimethyl-(2-[1,4]thiaborinan-4-yloxy-ethyl)- N SBO amine 108 (Scheme 26)[39]. N 107 Dibutyl ester of vinylboronic acid 109 reacted with 108 64-66% 2-mercaptoethanol 110 to form heterocyclic compound Scheme 26 of 2-butoxy-[1,5,2]oxathiaborepane 111 (Scheme 27) [40]. Bu O B +HS S B OBu β OH Synthesis and stereochemistry -S-substituted Bu O O olefins 109 110 111 Pasto and Snyder [41] prepared β-substituted Scheme 27

Eurasian ChemTech Journal 4 (2002) 153-167 V.M. Dembitsky et al. 163 organoboranes by deuteroboration. Addition of deu- group being strongly electron withdrawing, and hence teroborane (n-Pr)2BD to cis-β-phenylmercaptosterene reducing the electron density on the sulfur (Scheme 112 and trans-β-benzylmercaptostyrene 116 produced 28) [41,42]. the corresponding cis- and trans- β-sulfanylalkyl- bo- Reactions of thiols with ethylene boron compounds ranes 113 and 117. The interaction between the boron and sulfur was not sufficient to lead to cis elimination Woods and Bengelsdorf [43] obtained β-sulfanyl- 114. The inability to affect an acid catalyzed elimina- alkylborane 120 by addition of 1-hexanethiol 119 to tion with was also probably due to too weak interac- 2-vinyl-4,4,6-trimethyl-1,3,2-dioxaborinane 118 tions between the sulfur and BF3. β-Boryl alkyl (Scheme 29). The lower reactivity of 118 in this reac- thioether intermediate 113 underwent a facile trans tion indicated a reduced stability of intermediate 120 elimination in the presence of n-butyllithium 115 and compared with di-n-butyl ethyleneboranate 109 which 118. Deuterioboration of 116 gave also β-boryl alkyl reacted also with 1-hexanethiol to give dibutoxy-(2- thioether as intermediate 117 which did not undergo hexylmercaptoethyl)borane 121. This compound has an uncatalized elimination. Treatment 117 with BF3 also been obtained by other researchers [44,45]. produced trans-β-deuteriostyrene via a trans elimin- Mikhailov and Nikolaeva [46] reported that tris- ation. The difference in the reactivity 113 and 117 (2-brom-octyl)boran 122 reacted with butane-1-thiol must be due to the difference in the electronic effects to form the butyl ester of bis-(2-butylmercapto- of the groups bonded to the sulfur atom, the phenyl octyl)borin 123 (Scheme 30).

R RR BD BD H5C6 H H5C6 SC6H5 R cis C=C C=C H5C6 SC6H5 H D H H C C trans 114 112 H H 113 H5C6 D C=C H H 115 RR R BD BD H5C6 SCH2C6H5 R C=C H5C6 H trans C C H5C6 D H H C=C 116 H SCH2C6H5 117 H H

R=C3H7 Scheme 28

S O B hν O O B + HS (C6H13)2S O -70oC 119 118 120 Bu O S ν B HS h B + O O Bu O -70oC Bu Bu 109 121 Scheme 29

SC4H9 B(CH2CHBrC6H13)3 +n-C4H9SH B(CH2CHC6H13)3

122 123 Scheme 30

Eurasian ChemTech Journal 4 (2002) 153-167 164 Boranes in Organic Chemistry (2)

− Reactions of ethanethiol with dioxaborolanes have Reaction of boronic acid with NaSO3 been studied by Braun [47] and obtained some β-sulfur derivatives 124 - 126. The author showed that 2- According to Matteson et al. [40] the dibutyl ester − propenyl-[1,3,2]dioxaborolane reacted with ethane- of vinylboronic acid reacted with NaSO3 on an ion- thiol to give 2-(2-ethylsulfanyl-propyl)-[1,3,2]dioxa- exchange resin (H+ form) to give 2-boronoethane- borolane 124. Also 2-isopropenyl-[1,3,2]dioxa- sulfuric acid 129 (Scheme 34). borolane reacted with ethanethiol to form 2-(2- ethylsulfanyl-1-methyl-ethyl)-[1,3,2]dioxaborolane Bu O - Bu O NaSO3 125, and 2-(2-methyl-propenyl)-[1,3,2]dioxaborolane B B O reacted with ethanethiol to form 2-(2-ethylsulfanyl- Bu O Bu O SOH 2-methyl-propyl)-[1,3,2]dioxaborolane 126 (Scheme O 31). 129 Scheme 34

Reactions of thiocarboxylic acids

o O SH + 150 C S B B The thioacetic acid 130 reacted with dibutyl ester O 2-5 hrs O O of vinylboronic acid to form dibutyl-2-acetylthio- ethaneboronate 131. Similarly 3-mercaptopropionic 124 acid 132 reacted with the dibutyl ester of vinylboronic O 150oC S acid to form 3-(2-boronethylthio)-propionic acid 133 SH + B O B (Scheme 35). Also the dibutyl ester of isopropenyl- O 2-5 hrs O boronic acid reacted with 3-mercaptopropionic acid 125 132 to form 3-(2-boron-1-propylthio)propionic acid 134 [40].

O 150oC S SH + B O O B HO O 2-5 hrs OH O HS AIBN + B O O H2O S O Bu 126 O B Bu 131 Scheme 31 130 Bu O Bu

AIBN O S O Bu Reaction between the dibutyl ester of vinylboronic HS OH + B B O H2O acid with ethanethiol formed dibutyl-(2-ethylmercapto- O HO 133 O Bu O Bu ethylboronate) 127 (Scheme 32) [39]. Bu 132

S Bu O AIBN O O Bu irradiation O Bu HS OH + B B B + HS S O H2O B O HO O Bu Bu O O Bu 134 127 O Bu Bu Scheme 32 Scheme 35

Also β-sulfanylalkylboranes 128 could be obtained in the reaction of 2-amino-ethanethiol with the dibu- Braun and coworkers [47] have also been studied tyl ester of vinylboronic acid (Scheme 33) [40]. reactions of the ethyl ester of mercaptoacetic acid 135 with different dioxaborolanes 136 - 138. Thus, 2-vinyl-[1,3,2]dioxaborolane reacted with mercaptoacetic S acid ethyl ester to form the ethyl ester of (2-[1,3,2]di- O H2N B HCl oxaborolan-2-yl-ethylsulfanyl)-acetic acid 136, and 2- H2N SH O + O B 1. AIBN propenyl-[1,3,2] dioxaborolane reacted with ethyl es- 2. H2O 128 O ter of mercaptoacetic acid to form the ethyl ester of Scheme 33 (2-[1,3,2]dioxaborolan-2-yl-1-methyl-ethylsulfanyl)-

Eurasian ChemTech Journal 4 (2002) 153-167 V.M. Dembitsky et al. 165 acetic acid 137. 2-Isopropenyl-[1,3,2]dioxaborolane give the ethyl ester of (2-[1,3,2]dioxaborolan-2-yl- reacted with the ethyl ester of mercaptoacetic acid to propylsulfanyl)-acetic acid 138 (Scheme 36).

O O HS 150oC O + B S O O O O B 136 136 O

O O o HS 150 C O + B S O O O O B O 137

O O o HS 150 C O + B S O O O O B O 138 Scheme 36

Matteson et al. [40] have also been studied the (phenylmercaptoethyl)-N-triphenylborazine 145 reactions of vinylboronic acids with thiodicaboxylic (Scheme 38) [48]. and thioamino acids. Thus, mercaptosuccinic acid 139 reacted with the dibutyl ester of vinylboronic acid to Asymmetric hydroboration give (2-boron-ethylthio)bernstein acid 140. And cysteine 141 reacted with the dibutyl ester of vinylboronic Brown and Vara Prasad [49] studied hydroboration acid to form S-(2-boron-ethylthio)cysteine 142 (Sche- of 2,3-dihydrothiophene with diisopinocampheyl- me 37). borane. The authors showed that β-boryl alkyl thio- ethers 146 and 147 were intermediates. 147 was Synthesis of borazin derivatives converted to (+)-(R)-3-hydroxytetrahydro-thiophene 148 (Scheme 39). In a similar fashion 3,4-dihydrothia- B,B,B-Trivinyl-N,N,N-triphenylborazine 143 re- pyran was transformed to (R)-3-hydroxytetrahydro- acted with benzenethiol 144 in toluene to form B-tris- thiapyran 151 via β-sulfanylalkylboranes 149 and 150.

O HO HO S SH + O AIBN B Bu O O H2O HO O B Bu OH O O Bu O 140 Bu 139

O HS S HO O methanol H2N + B Bu heating NH2 O O B Bu OH Bu O 142 O 141 Bu Scheme 37

Eurasian ChemTech Journal 4 (2002) 153-167 166 Boranes in Organic Chemistry (2)

SH S N PhC O3H B B N + B B tol uene N N B N N B

144 145 S 143

Scheme 38

OH BIpc2 B(OEt)2 BIpc2 CH3CHO S S S S 146 147 148

BIpc2 B(OEt)2 OH BIpc2 CH3CHO

S S S S

149 150 151 Scheme 39

Diels-Alder reactions to be good dienophiles that reacted with cyclopentadiene to form β-sulfanylalkylboranes 153 and 154 Boronic esters such as the sulfone 152 were found [50,51] (Scheme 40).

O O O Ar B S B O O O SAr + O O OOS B 152 O Ar O

153 154 Scheme 40

References Organoborans. Springer-Verlag Berlin & Heidel- berg, 1995, p. 122. 4. Morin, C., Tetrahedron 50:12251 (1994). 1. V.M. Dembitsky and M. Srebnik, in M. Regitz 5. B.M. Mikhailov and Y.N Bubnov. Organoboron and D. Kaufmann (eds), Science of Synthesis, Compounds in Organic Synthesis. Bell & Bain, Houben-Weyl Methods of Molecular Transfor- Ltd., Glasgow, 1984. mation. Georg Thieme Verlag, Stuttgart, Ger- 6. H.C Brown. Boranes in Organic Chemistry. many, Chap. 32, 2003, in press. Cornell Univ. Press, Ithaca & London, 1972. 2. Wilkinson, J.S. Reviews of Boron Chemistry. 7. Kinder, D.H., and Ames, M.M., J. Org. Chem. Acad. Press, New York, 1997, p.148. 52:2452 (1987). 3. Matteson, D.S. Stereodirected Synthesis with 8. Lewis, J.W., and Pearce, A.A., Tetrahedron Lett.

Eurasian ChemTech Journal 4 (2002) 153-167 V.M. Dembitsky et al. 167

5:2039 (1964). and D. Kaufmann (eds), Science of Synthesis, 9. Lewis, J.W., and Pearce, A.A., J. Chem. Soc. 863 Houben-Weyl Methods of Molecular Transform- (1969). atio, Georg Thieme Verlag, Stuttgart, Germany, 10. Borowiyz, I.J., and Williams, G.J., J. Org. Chem. Chap. 30, 2002, in press. 32:4157 (1967). 32. Deng, Y., Chang, C.K., and Nocera, D.G., 11. Gore, J., Drouct, J.P., and Barieux, J.J., Tetrahe- Angew. Chem. Int. Ed. Engl. 39:1066 (2000). dron Lett. 1:9 (1969). 33. Kamatani, A., and Overman, L.E., J. Org. Chem. 12. Barieux, J.J., and Gore, J., Bull. Soc. Chim. 64:8743 (1999). France 1649 (1971). 34. Bittner, G., Witte, H., and Hesse, G., Justus 13. Barieux, J.J., and Gore, J., Bull. Soc. Chim. Liebigs Ann. Chem. 713:1 (1968). France 3978 (1971). 35. Sucrow, W., Zuhlke, L., and Slopianka, M., 14. Marshall, J.A., and Johnson, W.S., J. Org. Chem. Chem. Ber. 110:2818 (1977). 28:421 (1963). 36. Caron-Sigaut, C., Le Men-Oliver, L., Hugel, G., 15. Lyle, R.E., Carle, K.R., Ellefson, C.R., and Levy J., and Le Men, J., Tetrahedron 35:957 Spieer, C.K., J. Org. Chem. 35:802 (1970). (1979). 16. Lyle, R.E., and Spieer, C.K., Tetrahedron Lett. 37. Matteson, D.S., Soloway, A.H., Tomlinson, 11:1133 (1970). D.W., Campbell, J.D., and Nixon, G.A., J. Med. 17. Polivka, Z., and Ferles, M., Coll. Czech. Chem. Chem. 7:311 (1964). Comm. 36:4099 (1971). 38. Mikhailov, B.M., Shchegoleva, T.A., and 18. Lyle, R.E., McMahon, D.H., Krueger, W.E., and Shashkova, E.M., Zh. Obshch. Khim. 44:2193 Spieer, C.K., J. Org. Chem. 31:4164 (1966). (1974). 19. Ferles, M., Hauer, J., Kalar, J., Polivka, Z., and 39. Matteson, D.S., J. Org. Chem. 27:275 (1962). Stern, P., Coll. Czech. Chem.Comm., 37:2464 40. Matteson, D.S., Soloway, A.H., Tomlinson, (1972). D.W., Campbell, J.D., Nixon, G.A., J. Med. 20. Stern, P., Trska, P., and Ferles, M., Coll. Czech. Chem. 7:640 (1964). Chem.Comm. 39:2267 (1974). 41. Pasto, D.J., and Snyder, R., J. Org. Chem. 21. Fujita, Y., Irreverre, F., and Witkop, B., J. Amer. 31:2777 (1966). Chem. Soc. 86:1844 (1964). 42. Pasto, D.J., Cumbo, C.C., and Balasubramanu- 22. Allred, E.L., Anderson, C.L., and Smith, R.L., yan, P., J. Amer. Chem. Soc. 88:2187 (1966). Tetrahedron Lett. 7:951 (1966). 43. Woods, W.G., and Bengelsdorf, I.S., J. Org. 23. Allred, E.L., Anderson, C.L., and Smith, R.L., Chem. 31:2769 (1966). J. Org. Chem. 31:3493 (1966). 44. Matteson, D.S., J. Amer. Chem. Soc. 81:5004 24. Allred, E.L., and Smith, R.L., J. Org. Chem. (1959). 31:3498 (1966). 45. Matteson, D.S., J. Amer. Chem. Soc. 82:4228 25. Goranski, C.T., Singaram, B., and Brown, H.C., (1960). J. Org. Chem. 52:4014 (1987). 46. Mikhailov, B.M., and Nikolaeva, M.E., Izv. 26. Singaram, B., Rangaishenvi, M.V., Brown, H.C., Akad. Nauk SSSR Ser. Khim. 1368 (1963). Goranski, C.T., and Hasha, D.L., J. Amer. Chem. 47. Braun, J., C.R. Hebd. Seances Acad. Sci. 260:218 Soc. 111:384 (1989). (1965). 27. Singaram, B., Goranski, C.T., Rangaishenvi, 48. Seyferth, D., and Takamizawa, M., J. Org. Chem. M.V., and Brown, H.C., J. Org. Chem. 56:1543 28:1142 (1963). (1991). 49. Brown, H.C., and Vara Prasad, J.V.N., J. Amer. 28. Butler, D.N., and Soloway, A.H., J. Amer. Chem. Chem. Soc. 108:2049 (1986). Soc. 88:484 (1966). 50. Martinez-Fresneda, P., and Vaultier, M., Tetra- 29. Paetzold, P., and Kosma, S., Chem. Ber. 112:654 hedron Lett. 30:2929 (1989). (1979). 51. Rasset, C., and Vaultier, M., Tetrahedron 32:3397 30. Paetzold, P.I., and Grundke, H., Synthesis 635 (1994). (1973). 31. V.M. Dembitsky, and M. Srebnik, in M. Regitz Received 29 March 2002.

Eurasian ChemTech Journal 4 (2002) 153-167