Photosensitizer-Free Synthesis of Arylsulfonated 4,5-Fused Polycyclic Coumarin Derivatives via Photoinduced Cascade Sulfonylation/Cyclization of 4-(N-Alkyl-N-acrylamido)coumarins.

Abstract

A practical visible-light-induced cascade sulfonylation/cyclization of 4-(N-alkyl-N-acrylamido)coumarins bearing unactivated alkenes with arylsulfonyl chlorides has been developed for the synthesis of arylsulfonylated 4,5-fused polycyclic coumarin derivatives. The reaction proceeds at room temperature under external photosensitizer-, base-, and oxidant-free conditions. This protocol features mild conditions, a broad substrate scope, good functional group tolerance, and moderate to excellent yields. Synthetic utility was further demonstrated by a gram-scale reaction and successful irradiation with natural sunlight. Additionally, preliminary mechanistic studies support a radical cascade pathway initiated by energy transfer (EnT) from the photoexcited 4-(N-alkyl-N-acrylamido)coumarin framework to arylsulfonyl chlorides, followed by S-Cl bond hemolysis and intramolecular cyclization.