Rhodium-catalyzed enantioselective conjugate addition of organoboronic acids to alpha,beta-unsaturated sulfones

reaction: see text] A general method for the enantioselective catalytic conjugate addition to acyclic alpha,beta-unsaturated sulfones is described. Using metal-chelating alpha,beta-unsaturated pyridyl sulfones as substrates, the rhodium-catalyzed chiraphos-mediated addition of organoboric acids takes place in excellent yield and high enantioselectivity. The subsequent elimination of the pyridylsulfonyl group by Julia-Kociensky olefination provides a novel approach to the enantioselective synthesis of allylic substituted alkenes.