Chiral Indolizidine Synthesis through the Ir-Catalyzed Asymmetric Hydrogenation of Cyclic Pyridinium Salts.

The Ir-catalyzed asymmetric hydrogenation of cyclic pyridinium salts is presented as a new strategy for the convenient and efficient synthesis of chiral indolizidines. The asymmetric hydrogenation of cyclic pyridinium salts derived from 2-(2-acylphenyl)pyridines proceeded smoothly in the presence of [Ir(cod)Cl]2 and (R)-DM-SegPhos to provide the desired chiral 7,8-benzoindolizidines 6 in high to excellent yields with moderate enantioselectivity (up to 86:14 er) and excellent diastereoselectivity (>20:1 dr). The enantiomeric purity of 6j was increased to 92:8 through recrystallization.