Photocatalytic Sulfonylcarbocyclization of Alkynes Using SEt as a Traceless Directing Group: Access to Cyclopentenes and Indenes

Abstract Cyclopentenes and indenes are important structural scaffolds in synthetic, medical, and material chemistry. Cyclization of alkynes via remote C−H functionalization is an appealing approach to construct these motifs due to its high efficiency and step‐economy. Herein, a traceless directing group strategy was designed to reverse the regioselectivity of radical addition which enabled an unprecedented photocatalytic sulfonylcarbocyclization of terminal alkynes by forming C−C bond on inert C(sp 3 )−H bond. It offers a facile access to decorated cyclopentenes and indenes under mild conditions. The resultant products could be converted into a set of valuable molecular scaffolds, including a key intermediate of AM‐6226. Mechanistic experiments suggest a radical cascade pathway comprising a Markovnikov‐type sulfonylation, 1,5‐hydrogen atom transfer, 5‐endo‐trig cyclization, and β‐elimination. This study lays further groundwork for the use of anti‐Baldwin 5‐endo‐trig radical cyclization in rapidly assembling five‐membered carbocycles.