The chemistry of trichlorosilyl enolates. Aldol addition reactions of methyl ketones

Article abstract of DOI:10.1021/ja001023g

Investigations on the aldol addition chemistry of trichlorosilyl enolates derived from methyl ketones are presented in full. These trichlorosilyl enolates are competent aldol reagents in the absence of additives, reacting with aldehydes at ambient temperature to provide high yields of aldol adducts. When either enol or aldehyde partner bears a stereogenic center, low diastereoselectivity is observed in this uncatalyzed aldol process. The aldol additions are dramatically accelerated by the addition of catalytic quantities of chiral phosphoramides, particularly one derived from N,N'-dimethylstilbene-1,2-diamine. In this catalyzed mode, good to high enantioselectivities are obtained with a variety of achiral trichlorosilyl enolates and aldehydes. When either partner bears a stereogenic center, high diastereoselectivities are obtained with one enantiomer of the catalyst (matched case), while the other enantiomer provides low diastereoselectivity (mismatched case). The reaction scope, optimization of conditions, and stereoselection events are also discussed.