Cooperative Catalysis: Radical Addition to Olefins and Asymmetric Protonation

Key words

enantioselective protonation - conjugate addition - cooperative catalysis - azaarenes

Significance

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.

Comment

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.