Chemistry of silylketenes: a simple preparation of α-silyl-α-stannylacetic esters and their stereoselective Reformatsky-type reaction with aldehydes or aldimines

Abstract

Silylketenes 1a, b reacted smoothly with alkoxystannanes 3 to give the corresponding α-silyl-α-stannylacetates 4 almost quantitatively. Treatment of 4 with TiCl₄ caused selective cleavage of the C–Sn bond to bring about Reformatsky-type reaction with aldehydes 6 giving β-hydroxy-α-silyl esters 7. These two steps were carried out by one-pot operation, and variously substituted compounds 7 were obtained with high syn-selectivity (52–96% d.e.) in 41–89% yields. A similar one-pot procedure starting from 1a–c, 3, and aldimines 11 also provided the corresponding β-amino-α-silyl esters 12 with excellent syn-selectivity (96% d.e.) in 64–94% yields. Stereocontrolled preparation of both (E)- and (Z)-α,β-unsaturated esters 8 and a syn-amino diol derivative 17 from syn-7 and syn-12, respectively, is also described.