Carbohydrate-derived thiols as protic polarity-reversal catalysts for enantioselective radical-chain reactions
A variety of novel homochiral carbohydrate-derived thiols, in which the SH group is attached to the anomeric carbon atom, have been prepared and characterised. These thiols have been evaluated as protic polarity-reversal catalysts to mediate the enantiose
Cai, Yudong,Roberts, Brian P.,Tocher, Derek A.
p. 1376 - 1386
(2007/10/03)
Enantioselective radical-chain hydrosilylation of alkenes using homochiral thiols as polarity-reversal catalysts
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°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 β-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-β-D-glucopyranose and 1-thio-β-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.
Haque, M. Bodrul,Roberts, Brian P.,Tocher, Derek A.
p. 2881 - 2889
(2007/10/03)
More Articles about upstream products of 214768-77-1