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Vanadium-Catalyzed Regioselective Oxidative Coupling of 2‑Hydroxycarbazoles

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posted on 15.01.2016, 12:06 by Lei Liu, Patrick J. Carroll, Marisa C. Kozlowski
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.