Highly Enantioselective Synthesis of (2-Pyridyl)phosphine Based C-Chiral Unsymmetrical P,N-Ligands Using a Chiral Palladium Complex

The organopalladium complex containing ortho-metalated (R)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary has been used to promote the asymmetric hydrophosphination reactions of diphenylphosphine with (E)-1-phenyl-3-pyridin-2-yl-2-propenone and (E)-1-methyl-3-pyridin-2-yl-2- propenoate in high regio- and stereoselectivities under mild conditions. Hydrophosphination of (E)-1-phenyl-3-pyridin-2-yl-2-propenone with diphenylphosphine generated two stereoisomeric products in a ratio of 8:1 as five-membered 2-pyridylphosphine P−N bidentate chelates on the chiral naphthylamine palladium template. Using the same chiral metal template, the corresponding hydrophosphination reaction of (E)-1-methyl-3-pyridin-2-yl-2-propenoate gave only one product as a six-membered P−N bidentate chelate. The naphthylamine auxiliary could be removed chemoselectively from the template product by treatment with concentrated hydrochloric acid to form the corresponding optically pure neutral complexes. Subsequent ligand disp...