Visible‐Light‐Induced Radical Sulfonylative‐Cyclization Cascade of 1,6‐Enynol Derivatives with Sulfinic Acids: A Sustainable Approach for the Synthesis of 2,3‐Disubstituted Benzoheteroles

Abstract

AbstractBenzoheteroles are promising structural scaffolds in the realm of medicinal chemistry, but sustainable synthesis of 2,3‐difunctionalized benzoheterole derivatives is still in high demand. Indeed, we have conceptually rationalized the intrinsic reactivity of propargylic‐enyne systems for the flexible construction of 2,3‐disubstituted benzoheteroles through radical sulfonylative‐cyclization cascade under organophotoredox catalysis. We hereby report an efficient visible‐light‐induced sulfonyl radical‐triggered cyclization of 1,6‐enynols with sulfinic acids under the dual catalytic influence of 4CzIPN and NiBr2⋅DME, which led to the formation of 2,3‐disubstituted benzoheteroles in good to high yields. Additionally, the Rose Bengal (RB)‐catalyzed radical sulfonylative‐cycloannulation of acetyl‐derived 1,6‐enynols with sulfinic acids under blue LED irradiation allowed to access 3‐(E‐styryl)‐derived benzofurans and benzothiophenes in moderate to good yields. The scope and limitations of the present strategies were successfully established using different classes of 1,6‐enynols and sulfinic acids bearing various sensitive functional groups, yielding the desired products in a highly stereoselective fashion. Plausible mechanistic pathways were also proposed based on the current experimental and control experiments.