Cu-Mediated Sulfonyl Radical-Enabled 5- exo-trig Cyclization of Alkenyl Aldehydes: Access to Sulfonylmethyl 1 H-Indenes.

An efficient method for the construction of sulfonylmethyl 1 H-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.