Synthesis of enantiopure beta- and gamma-amino alcohols from homochiral alpha- and beta-aminoacylsilanes as stable synthetic equivalents of alpha- and beta-amino aldehydes

A practical route is described for the synthesis of enantiopure beta- and g amma-amino alcohols with two stereocenters, starting from homochiral alpha- (1 and 5) and beta- (13 and 16) -aminoacylsilanes, and involving stereosel ective addition of allylmetal compounds and subsequent stereospecific proti odesilylation of the adducts. The degree of diastereoselectivity achieved i n the nucleophilic addition step depends on both the nitrogen-protecting gr oup and the reagents used. Diastereomeric excess (de) values equal to or hi gher than 98% were obtained in the TiCl4-promoted allylation of the N-Pht-a minoacylsilanes 1 and 13 and of the N-Ts-aminoacylsilane 5 with allyltrimet hylsilane. Lower de values were obtained in the Sc(OTf)(3)-catalyzed allyla tion of 5 with tetraallyltin and in the additions of both allyltrimethylsil ane and tetraallyltin to the N-Ts-beta-aminoacylsilane 16. Protiodesilylati on of the adducts, leading to the beta- and gamma-amino alcohols, was accom plished with TBAF, except in the case of the adducts obtained from 5. For t hese, a preliminary removal of the tosyl group was necessary. which was acc omplished with simultaneous desilylation by treatment with Na in Liquid amm onia.