Copper/Diboron-Mediated Intramolecular Oxygenation and Allylation/Benzylation of Nitroalkynes for the Synthesis of C2-Quaternary Indolin-3-ones.

A direct strategy for intramolecular transfer oxygenation of alkynes and cycloisomerization of 2-nitroalkynes to synthesize a wide range of C2-quaternary indolin-3-ones was developed by a copper/diboron system. The desired allylation, benzylation and propargylation products were obtained in moderate to excellent yields with good functional group tolerance. The mechanism study indicated that this protocol involved a radical process.