Copper-mediated oxidative direct C–C (hetero)aromatic cross-coupling

Abstract

Some new types of copper-mediated intermolecular oxidative direct C–C (hetero)aromatic cross-couplings are described. A combination of the simple CuCl₂ salt and molecular oxygen allows 1,3-azoles to couple with terminal alkynes directly to form the corresponding heteroarylacetylenes. This direct version of Sonogashira-type coupling can be applied to the reaction with polyfluoroarenes. A copper acetate complex enables direct biaryl coupling between 2-arylazines and 1,3-azoles even in the absence of any palladium catalysts. Moreover, the Cu-based protocol can be extended to the coupling with indoles and pyrroles, in which a catalytic variant is also possible by using an ideal co-oxidant, atmospheric oxygen. On the other hand, a copper-promoted annulative direct coupling of o-alkynylphenols and -anilines with 1,3-azoles can provide a unique dehydrogenative approach to C3-azolylbenzoheteroles from nonhalogenated and nonmetalated starting materials. In addition, a related N-azolylindole synthesis from similar substrates is also disclosed.