A hydrazine-free photoredox catalytic synthesis of azines by reductive activation of readily available oxime esters

Abstract

Herein, we present a novel, hydrazine-free photoredox catalyzed platform for azine synthesis using mild, simple reaction conditions. While previous energy transfer activations of oxime esters lead to decarboxylation of the O-auxiliary and radical combination with the iminyl radical, the reductive electron transfer strategy herein affords high yields of azines using only a triarylamine organophotocatalyst and no additives. Scale up was readily achieved by means of a continuous flow reactor. Mechanistic studies indicate a preassembly of photocatalyst and substrate is key to achieving efficient and selective N–N iminyl radical coupling.