Photoredox copper-catalyzed regioselective syntheses of allenols via HAT-mediated propargyl radical generation

Abstract

Selectivity control of the reactions of propargylic and/or allenylic radicals remains particularly elusive. Here, a visible light-mediated Cu-catalyzed protocol for the highly selective syntheses of tri- and tetra-substituted allenols from alkynol derivatives has been developed. Synthetic potentials of the products have been demonstrated. The control experiments, Stern-Volmer quenching, and cyclic voltammetry studies support a reaction pathway involving the generation of allenyl radicals via photo-mediated N-O bond scission, intramolecular 1,5-HAT process, the resonance to propargylic radicals, and coupling. Non-common intramolecular 1,6-HAT process has also been observed.