DABCO‐Mediated Photoelectrochemical Three‐Component Sulfonocyclization of 3‐Aza‐1,5‐dienes.

Comprehensive Summary Herein, we report a rare example of three‐component net‐oxidative sulfonylation of a SO2 surrogate with an oxidatively activated radical precursor under mild and metal‐ and external‐oxidant‐free conditions. The mildness and sustainability of the reaction are enabled by photoelectrocatalysis, and 3‐aza‐1,5‐dienes, organotrifluoroborates and 1,4‐diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO) undergo sulfonylative cyclization to afford sulfono 4‐pyrrolin‐2‐ones in an atom‐economical manner with a broad substrate scope and good functional‐group tolerance. The protocol is amenable to the late‐stage diversification of complex molecular architectures as well as the gram‐scale synthesis. Sunlight could be used as the light source, and the reaction could be conducted in an all‐solar mode using a commercially available photovoltaic panel to generate electricity in situ. Mechanistic studies reveal that the in situ generated 1,4‐diazabicyclo[2.2.2]octane (DABCO), which was generally innocent in previous reactions, functions as an electron shuttle between the photocatalytic cycle and the reactants. [ABSTRACT FROM AUTHOR]