Metal-free photoredox-catalyzed reductive dimerization of allenes enabled by heterolytic cleavage of α-bromo esters: Access to functionalized 1,5-dienes

Abstract

Selective functionalization of allenes is an actively researched area in synthetic chemistry yet faces challenges, including regio- and stereoselectivity. Herein, we report a metal-free photoredox catalyzed reductive dimerization of allenes with α-bromoesters under blue light irradiation. The reaction proceeds with wide range of 1,1-di substituted symmetrical and unsymmetrical allenes along with α-bromoesters to generate a novel series of di-alkyl substituted 1,5-diene molecules. Mechanistic studies, including photo physical studies, radical trapping experiments, intermediate capture experiments, Stern-Volmer experiments, and DFT studies confirm that the reaction was initiated by selective radical addition of in-situ generated alkyl ester radical to allene, followed by allyl-allyl radical pairing. The transformation proceeds under mild, environmentally benign conditions, highlighting the potential of organophotoredox catalysis as a green and efficient strategy for constructing complex diene frameworks.