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

Abstract

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.