Cu-Mediated Sulfonyl Radical-Enabled 5-<i>exo-trig</i> Cyclization of Alkenyl Aldehydes: Access to Sulfonylmethyl 1<i>H</i>‑Indenes

An efficient method for the construction of sulfonylmethyl 1H-indenes via Cu­(I)-mediated sulfonyl radical-enabled 5-exo-trig cyclization of alkenyl aldehydes has been developed for the first time. Mechanistic studies indicated that a radical addition–cyclization–elimination (RACE) process might be involved. The reaction features a relatively broad substrate scope, good annulation efficiency, and varying functional group tolerance.