Silver-Catalyzed Allenylation and Enantioselective Propargylation Reactions of Ketones

摘要

Homopropargylic alcohols have garnered significant interest as useful building blocks for complex molecule synthesis. This structural motif is frequently formed through the addition of propargylic nucleophiles to the corresponding aldehyde or ketone. Early advances focused on the development of stoichiometric addition reactions of chiral allenylboron reagents to aldehydes. In the early 1990s, the first catalytic asymmetric methods to form chiral secondary alcohols were reported, spurring renewed interest in the field. Additions to aldehydes have been extensively studied and new asymmetric catalysts have recently been identified for enantioselective propargylation reactions of ketones, which employ propargyl- or allenylboron reagents or prop-argyl bromide as starting materials, to form the corresponding tertiary alcohols. Several of these catalyst systems provide high enantioselectivity in additions to methyl ketones. Enantioselective propargylation reactions of prochiral diaryl ketones have not been reported, however. Herein, we report silver-catalyzed allenylation and propargylation reactions on a wide range of ketones (Scheme 1).