Enantioselective synthesis of α-aryl α-hydrazino phosphonates.

Catalysts generated in situ by the combination of pyridine-hydrazone N , N -ligands and Pd(TFA) 2 have been applied to the addition of arylboronic acids to formylphosphonate-derived hydrazones, yielding α-aryl α-hydrazino phosphonates in excellent enantioselectivities (96 → 99% ee). Subsequent removal of the benzyloxycarbonyl (Cbz) N -protecting group afforded key building blocks en route to appealing artificial peptides, herbicides and antitumoral derivatives. Experimental and computational data support a stereochemical model based on aryl-palladium intermediates in which the phosphono hydrazone coordinates in its Z -configuration, maximizing the interactions between the substrate and the pyridine-hydrazone ligand.