Conjugate Addition-Enantioselective Protonation of N-Aryl Glycines to alpha-Branched 2-Vinylazaarenes via Cooperative Photoredox and Asymmetric Catalysis

An enantioselective protonation strategy has been successfully applied to the synthesis of chiral a-tertiary azaarenes. With a dual catalytic system involving a chiral phosphoric acid and a dicyanopyrazine-derived chromophore (DPZ) photosensitizer that is mediated by visible light, a variety of a-branched 2-vinylpyridines and 2-vinylquinolines with N-aryl glycines underwent a redox-neutral, radical conjugate addition-protonation process and provided valuable chiral 3-(2-pyridine/quinoline)-3-substituted amines in high yields with good to excellent enantioselectivities (up to >99% ee). An application of this methodology to a two-step synthesis of the enantiomerically pure medicinal compound pheniramine (Avil) is also presented.