Enol Acetates: Versatile Substrates for the Enantioselective Intermolecular Tsuji Allylation.

Abstract

A highly versatile enantioselective intermolecular Tsuji allylation that generates alpha-quaternary stereocenters is reported. The methodology utilizes a prochiral enol acetate as a substrate, which is the last class of the original Tsuji substrates to be successfully employed in an enantioselective variant of the venerable reaction. This development enables a highly convergent approach that lends itself to rapid diversification and analogue synthesis by facilitating the incorporation of the allyl moiety from an allylic alkoxide, obviating the need for the preparation of allylic enol carbonates. The reaction is operationally simple and employs the readily available PHOX ligand class. More than 30 examples are reported that proceed with enantiomeric excess (ee) values of up to 96% and a scope that tolerates a wide range of functional groups on the allylic component. The enol acetate substrates are readily prepared from both aryl and aliphatic ketones, where the regioselective preparation has long been known utilizing a variety of methods. The power of this methodology lies in its ability to quickly produce a diverse set of single enantiomer products using different allylic alcohols with a common prochiral enol acetate. This is demonstrated here by two rapid formal syntheses of hamigeran B that utilize a common intermediate to intercept both Clive and Stoltz intermediates, and also to prepare novel intermediate analogues.