Access to 3a-Benzoylmethyl Pyrrolidino[2,3-<i>b</i>]indolines via Cu^II-Catalyzed Radical Annulation/C3-Functionalization Sequence

Abstract

A Cu^II-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 Cu^II-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.