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

Investigations on the aldol addition chemistry of trichlorosilyl enolates d erived from methyl ketones are presented in full. These trichlorosilyl enol ates are competent aldol reagents in the absence of additives, reacting wit h aldehydes at ambient temperature to provide high yields of aldol adducts. When either enol or aldehyde partner bears a stereogenic center, low diast ereoselectivity is observed in this uncatalyzed aldol process. The aldol ad ditions are dramatically accelerated by the addition of catalytic quantitie s of chiral phosphoramides, particularly one derived from N,N'-dimethylstil bene-1,2-diamine. In this catalyzed mode, good to high enantioselectivities are obtained with a variety of achiral trichlorosilyl enolates and aldehyd es. When either partner bears a stereogenic center, high diastereoselectivi ties 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.