Visible-Light Mediated Divergent Synthesis of Sulfonylated Dihydropyrrole-3-Carboxaldehydes and Tricyclic Sulfones via Sulfonyl Radical Source Modulation.

In this study, we present a green and efficient photocatalytic strategy, where sulfonyl radical-triggered cyclization of 1,6-enynes enables the selective formation of the sulfonylated dihydropyrrole-3-carboxaldehydes and tricyclic benzofused seven-membered sulfones. The switchable nature of the strategy relies on the selective control between radical cyclization and radical cascade cyclization, dictated by the choice of sulfonyl radical source. Under the photocatalytic conditions, selenosulfonates yielded sulfonylated heterocyclic carboxaldehydes, while sodium aryl sulfinates led to the formation of tricyclic benzo-fused seven-membered sulfones. Under blue LED irradiation, selenosulfonates generate sulfonyl and phenylselenyl radicals. The sulfonyl radical adds chemoselectively to the alkene, triggering a 5-exo-dig cyclization to form a vinyl radical, which is trapped by the phenylselenyl radical. Oxygen and EY-Na₂ facilitate the conversion of selenosulfonylated intermediates into sulfonylated 4,5-dihydropyrrole-3-carboxaldehydes. A range of 4,5-dihydropyrrole-3-carboxaldehydes was synthesized using the developed method. Sodium aryl sulfinates, under blue LED irradiation and in the presence of 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP)1,1-Diphenylethylene, react with 1,6-enynes to afford tricyclic benzo-fused seven-membered sulfones. Additionally, the tricyclic sulfone can be readily transformed into a unique bicyclic seven-membered sulfone bearing an exocyclic double bond. A variety of control experiments was performed, providing important mechanistic understanding of both steps in the transformation.