Synthesis of Optically Active Piperidines by Enantioselective Addition Reaction

Almqvist et al. have reported the synthesis of optically active piperidines by enantioselective addition of aryl Grignard reagents to pyridine N-oxides followed by reduction. According to their results, the addition reactions proceed enantioselectively to give N-hydroxytetrahydropyridines by using Li-(+)-BINOL-ate, which is generated from (R)-(+)-BINOL and phenyl lithium, as a chiral ligand. Subsequent reduction affords optically active piperidines in high yields with high optical purities. BINOL is both easily removed and recovered from the crude reaction mixture.