Bisphosphonium-catalyzed ring-opening of cycloalkenes under visible-light irradiation†

Abstract

The selective cleavage of CC double bonds to form carbonyl groups is a fundamental maneuver in retrosynthetic analysis, empowering swift alterations to molecular structures and efficient synthesis of sophisticated, multifunctional molecules. Traditional methods like ozonolysis are effective but come with safety, environmental, and economic challenges. To address these concerns, photochemical methods have recently emerged as ideal platforms for alkene oxidative cleavage through the utilization of photons as energy sources and open-shell radicals as reactive intermediates. Herein, we disclose an oxidant-free, operationally simple, and environmentally friendly protocol for the oxidative cleavage of cyclic alkenes via in situ-generated secondary alcohol intermediates. Facilitated by a bisphosphonium catalyst, the selective integration of alkoxy radical-mediated C–C bond scission with anti-Markovnikov alkene hydrofunctionalization led to the selective cleavage of cyclic alkenes and the formation of distal phenyl-substituted aldehydes with outstanding regioselectivity. This photocatalytic process accommodates both activated and unactivated cycloalkenes and operates under mild, redox-neutral conditions. Furthermore, the use of continuous-flow reactors has significantly improved photocatalytic efficiency, providing a robust and scalable solution for large-scale applications.