Cu-Catalyzed Aerobic Oxidative N-N Coupling of Carbazoles and Diarylamines Including Selective Cross-Coupling

A Cu-catalyzed method has been identified for aerobic oxidative dimerization of carbazoles and diarylamines to the corresponding N-N coupled bicarbazoles and tetraarylhydrazines. The reactions proceed under mild conditions (1 atm O-2, 60-80 degrees C) with a catalyst composed of CuBr.dimethylsulfide and N,N-dimethylaminopyridine. Reactions between carbazole and diarylamines show unusually selective cross-coupling, even with a 1:1 ratio of the two substrates. This behavior was found to arise from reversible formation of the tetraarylhydrazine. Formation of this species is kinetically favored, but cleavage of the N-N bond under the reaction conditions leads to selective formation of the thermodynamically favored cross-coupling product.