Highly Enantioselective Piers-Type Hydrosilylation of Structurally Diverse Ketones Catalyzed by Chiral Frustrated Lewis Pairs

Enantioselective reduction of ketones is a powerful and straightforward methodology for the synthesis of chiral secondary alcohols. However, various ketone substrates, including aryl/long-chain-alkyl, diaryl, dialkyl ketones, and diketones, remain challenging, and very few chiral catalysts are capable of addressing all these substrates. Notably, the ketone scope for asymmetric Piers-type hydrosilylation is even narrower. In this work, a biphenyl-based chiral diene-derived borane was developed, which coupled with phosphine as a frustrated Lewis pair catalyst for the asymmetric Piers-type hydrosilylation. In contrast to the binaphthyl-based catalyst, the present FLP catalyst exhibits unexpectedly high effectiveness toward aryl/long-chain-alkyl, diaryl, and dialkyl ketones, affording the corresponding optically active alcohols with high levels of enantioselectivities. For 1,n-diketones, the target alcohol products were obtained with both high diastereoselectivities and enantioselectivities. The mild reaction conditions and broad substrate scope make this protocol a promising approach for the synthesis of highly enantioenriched secondary alcohols.