Enantioselective radical-chain hydrosilylation of alkenes using homochiral thiols as polarity-reversal catalysts

被引:71
作者
Haque, MB [1 ]
Roberts, BP [1 ]
Tocher, DA [1 ]
机构
[1] Univ London Univ Coll, Dept Chem, Christopher Ingold Labs, London WC1H 0AJ, England
来源
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1 | 1998年 / 17期
关键词
D O I
10.1039/a803280g
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The thiol-catalysed radical-chain additions of triphenylsilane and of tris(trimethylsilyl)silane to a number of cyclic prochiral terminal alkenes have been carried out at 60 degrees C in the presence of di-tert-butyl hyponitrite as initiator. The function of the thiol catalyst is to promote the overall abstraction of hydrogen from the silane by the nucleophilic carbon-centred radical intermediate, formed by addition of the silyl radical to the alkene, and the stereogenic centre in the final adduct is set by hydrogen-atom transfer from the thiol to this beta-silylalkyl radical. When the thiol is homochiral the transfer of hydrogen becomes enantioselective and an optically active adduct results. A number of homochiral thiols were investigated and the highest enantiomeric excesses (up to 95%) were achieved using the tetra-O-acetyl derivatives of 1-thio-beta-D-glucopyranose and 1-thio-beta-D-mannopyranose. The absolute configuration of an enantiopure triphenylsilane adduct (upgraded by recrystallisation) was determined by X-ray crystallography and it was shown that this adduct could be oxidatively desilylated to the corresponding alcohol and acetate with no loss of enantiomeric purity.
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收藏
页码:2881 / 2889
页数:9
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