Phosphine‐oxide‐catalyzed Enantioselective Cross‐aldol Reactions of Aldehydes with Trichlorosilane as Lewis Acid Promoter

A hypervalent silicon complex between trichlorosilane and a chiral phosphine oxide acts as an effective Lewis acid mediator that successfully promotes highly enantioselective cross‐aldol reactions between two aldehydes. The high yielding transformation is realized with the assistance of triisobutylamine, which does not decompose trichlorosilane but rather converts the aldol donor into the silyl enol ether that undergoes the enantioselective cross‐aldol reaction with a second aldehyde in combination with the chiral phosphine oxide catalyst. Phosphine oxide catalysis with trichlorosilane. A hypervalent silicon complex formed between trichlorosilane and a chiral phosphine oxide acts as an effective Lewis acid mediator that successfully promotes the cross‐aldol reaction between two aldehydes with good‐to‐high enantioselectivity. The high yielding transformation is realized by the assistance of triisobutylamine, which effectively promotes the silyl enolization of an aldol donor, resulting in the cross‐aldol reaction with an aldol acceptor.