Access to 3a-Benzoylmethyl Pyrrolidino[2,3- b]indolines via CuII-Catalyzed Radical Annulation/C3-Functionalization Sequence.

A CuII-catalyzed radical annulation/C3-functionalization cascade of tryptamine derivatives with aryl ethylene is reported. The mild catalytic system enables the facile construction of 3a-benzoylmethylpyrrolidino[2,3- b]indolines with excellent chemo- and regioselectivities. Remarkably, this novel method utilizes earth-abundant and inexpensive cupric salt as the catalyst and air as the co-oxidant, rendering the process highly environmentally friendly and atom economic. Presumably, the reaction proceeds through CuII-initiated formation of pyrrolidino[2,3- b]indolines radical intermediate I, which is successively trapped by aryl ethylene and O2 to form the product. An 18O2-labeling experiment and several control experiments were designed to support the mechanistic proposal.