Photo and copper dual catalysis for allene syntheses from propargylic derivatives via one-electron process

Abstract

Different from the traditional two-electron oxidative addition-transmetalation-reductive elimination coupling strategy, visible light has been successfully integrated into transition metal-catalyzed coupling reaction of propargylic alcohol derivatives highly selectively forming allenenitriles: specifically speaking, visible light-mediated Cu-catalyzed cyanation of propargylic oxalates has been realized for the general, efficient, and exclusive syntheses of di-, tri, and tetra-substituted allenenitriles bearing various synthetically versatile functional groups. A set of mechanistic studies, including fluorescence quenching experiments, cyclic voltammetric measurements, radical trapping experiments, control experiments with different photocatalyst, and DFT calculation studies have proven that the current reaction proceeds via visible light-induced redox-neutral reductive quenching radical mechanism, which is a completely different approach as compared to the traditional transition metal-catalyzed two-electron oxidative addition processes.

Transition-metal-catalyzed couplings of propargylic alcohol derivatives with organometallic reagents proceeds via two-electron transformations, which present limitations in scope and selectivity. Here, the authors present visible-light-mediated copper-catalyzed cyanation of propargylic oxalates to form allenenitriles via a one-electron pathway