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Conjugate Addition–Enantioselective Protonation of N‑Aryl Glycines to α‑Branched 2‑Vinylazaarenes via Cooperative Photoredox and Asymmetric Catalysis

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posted on 2018-04-10, 00:00 authored by Yanli Yin, Yating Dai, Hongshao Jia, Jiangtao Li, Liwei Bu, Baokun Qiao, Xiaowei Zhao, Zhiyong Jiang
An enantioselective protonation strategy has been successfully applied to the synthesis of chiral α-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 α-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.

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