Highly enantioselective hydrogenation of β-acyloxy and β-acylamino α,β-unsaturated phosphonates catalyzed by rhodium phosphane-phosphite complexes

摘要

The 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. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.