Synthesis of highly substituted allylic alcohols by a regio- and stereo-defined CuCl-mediated carbometallation reaction of 3-aryl-substituted secondary propargylic alcohols with Grignard reagents.

A highly regio- and stereoselective CuCl-mediated carbometallation reaction of 3-aryl-substituted secondary propargylic alcohols with alkyl, aryl, vinyl or allyl Grignard reagents for the synthesis of fully-substituted allylic alcohols was developed. The R(2) group from the Grignard reagent was successfully introduced to the 2-position of the propargylic alcohols due to the chelation of metal atom with the hydroxyl oxygen atom forming 5-membered metallacyclic intermediates, which smoothly react with various electrophiles to afford stereodefined polysubstituted allylic alcohols. By this method, optically active allylic alcohols can be prepared from readily available optically active propargylic alcohols without obvious racemization. Five-membered lactones can also be synthesized by Pd-catalyzed carbonylation with iodoallylic alcohols.