One‐Pot Two‐Step Synthesis of Optically Active α‐Amino Phosphonates by Palladium‐Catalyzed Hydrogenation/Hydrogenolysis of α‐Hydrazono Phosphonates

Abstract

AbstractAn efficient and convenient one‐pot procedure for the stereoselective catalytic synthesis of ring‐substituted [amino(phenyl)methyl]phosphonates has been developed. The enantioselective hydrogenation of easily available diisopropyl (Z)‐[aryl(phenylhydrazono)methyl]phosphonates using palladium(II) acetate as a precatalyst, (R)‐2,2′‐bis(diphenylphosphino)‐5,5′‐dichloro‐6,6′‐dimethoxy‐1,1′‐biphenyl [(R)‐Cl–MeO‐BIPHEP] as a ligand, and (1S)‐(+)‐10‐camphorsulfonic acid as an activator in a mixture of 2,2,2‐trifluoroethanol and methylene chloride at ambient temperature results in the formation of corresponding [aryl(2‐phenylhydrazino)methyl]phosphonates. The subsequent cleavage of the N−N bond has been accomplished with molecular hydrogen after the addition of palladium on carbon and methanol into crude reaction mixture to afford the optically active [amino(aryl)methyl]phosphonates. The method is operationally simple and provides an appreciable enantioselectivity up to 98 % ee.magnified image