Cooperative Catalysis: Radical Addition to Olefins and Asymmetric Protonation
Conjugate Addition–Enantioselective Protonation of N-Aryl Glycines to α-Branched 2-Vinylazaarenes via Cooperative Photoredox and Asymmetric Catalysis.
J. Am. Chem. Soc. 2018;
18 June 2018 (online)
Jiang and co-workers report the enantioselective radical conjugate addition–protonation of N-aryl glycines to α-branched vinylazaarenes using a metal-free dual catalytic system (a photosensitizer and a chiral phosphoric acid). The corresponding products are obtained in high yields with good to excellent enantioselectivities, and the methodology is applied to the synthesis of the medicinal compound pheniramine.
Because α-amino acids are abundant, their use as starting materials for organic synthesis is desirable. In this report, N-aryl α-glycines undergo photooxidative decarboxylation and react further with highly activated olefins in a radical pathway followed by enantioselective protonation. While many examples are shown, the presented substrate scope is still limited to pyridine- and quinoline-containing substances.