Radical Cross Coupling and Enantioselective Protonation through Asymmetric Photoredox Catalysis

An unprecedented enantioselective protonation reaction enabled by photoredox catalytic radical coupling is developed. Under cooperative dicynopyrazine‐derived chromophore (DPZ) as a photosensitizer and a chiral phosphoric acid catalyst, and Hantzsch ester as a sacrificial reductant, the transformations between α‐substituted enones and cyanoazaarenes or 2‐(chloromethyl)azaaren‐1‐iums can proceed a tandem reduction, radical coupling, and enantioselective protonation process efficiently. Two classes of pharmaceutically important enantioenriched azaarene variants, which contain a synthetically versatile ketone‐substituted tertiary carbon stereocenter at the β‐ or γ‐position of the azaarenes, are synthesized with high yields and ees. The first radical coupling and enantioselective protonation is developed. Under cooperative photoredox and chiral hydrogen‐bonding catalysis, the transformations of α‐substituted enones with cyanoazaarenes or 2‐(chloromethyl)azaaren‐1‐iums could render two classes of valuable azaarene variants with high yields and ees, which contain a synthetically useful ketone‐substituted tertiary carbon stereocenter at the β‐ or γ‐position of the azaarenes.