Vanadium-catalyzed regioselective oxidative coupling of 2-hydroxycarbazoles

Abstract

The first regioselective oxidative coupling of 2-hydroxycarbazoles is described. With a vanadium catalyst and oxygen as the terminal oxidant, dimers with an ortho-ortho′ coupling pattern were obtained with high selectivity. Further oxidation led to ortho′-ortho′ coupling to generate a tetramer, which provided insight that the atropisomerization barriers of the unsymmetrical biaryl bonds are much lower than expected.