Four-component radical-polar crossover cyclization involving double insertion of SO2 to β-sulfonyl sultines

Abstract

Sulfur oxides are widespread and gaining increasing attention in pharmaceutical and biotechnology discoveries owing to their heightened activities, despite the fact that sulfur dioxide (SO₂) is one of the most harmful gaseous air pollutants. Considerable research efforts have been devoted to dealing with sulfur oxides in a greener and sustainable way. Herein, we report a visible-light-promoted four-component radical-polar crossover tandem cyclization involving twofold insertion of SO₂ and the formation of S(IV) and S(VI) centers in one procedure. Various types of functionalized β-sulfonyl sultines were afforded from easy-to-access C(sp²)–H and C(sp³)–H building blocks with high group compatibility under mild and operationally simple conditions. Gram-scale preparation and late-stage transformations demonstrate opportunities to rapidly construct molecular complexity. Mechanistic studies supported a SO₂ bi-inserted radical-polar crossover cyclization relay sequence, which allows for a more efficient utilization of SO₂ and is also more environmentally friendly.