Highly Enantioselective Hydrogenation of β‐Acyloxy and β‐Acylamino α,β‐Unsaturated Phosphonates Catalyzed by Rhodium Phosphane‐Phosphite Complexes

Abstract

AbstractThe enantioselective hydrogenation of β‐(acyloxy)‐ and β‐(acylamino)vinylphosphonates with rhodium catalysts based on chiral phosphane‐phosphite ligands has been studied. In the case of the β‐(acyloxy)vinylphosphonates, the reaction also produces an achiral phosphonate resulting from the elimination of the benzoate group. High ligand modularity has led to a highly chemo‐ and enantioselective catalyst for both types of substrates, which afford a good range of β‐acyloxy‐ and β‐acylaminophosphonates with enantioselectivities between 90 and 99% ee. Most interestingly, the configuration of the hydrogenation products indicates the same stereochemical sense for the reduction of both types of substrates, which is opposite to that observed before for α‐(acyloxy)vinylphosphonates. This observation has been rationalized by assuming the formation of a β‐alkyl intermediate during the catalytic cycle, which also explains the formation of the elimination product in the hydrogenation of the β‐(acyloxy)‐vinylphosphonates.