N-Heterocyclic carbene copper complex catalyzed Chan-Evans-Lam reactions of arylboronic acids with azoles and amines

Abstract

An efficient protocol of Chan-Evans-Lam reactions involving arylboronic acids and azole and amine derivatives was developed based on a series of N-heterocyclic carbene copper (Cu-NHC) complexes as the precatalysts. The relationship between the catalyst structure and catalytic properties was investigated in detail. The results demonstrated that the modification of NHC backbone with acenaphthyl group exhibited significant beneficial effect on the coupling efficiencies. Nonetheless, it appeared that more bulk on the N-aryl moieties of NHC ligands impeded the reactions. The protocol also features mild reaction conditions, such as low catalyst loading (0.1–1 mol%), non-toxic solvent and air as the sole oxidant, which highlights the usefulness of Cu-NHC as the precatalyst for this reaction.