Regioselective synthesis of unsymmetrical biheteroaryls via copper(ii)-catalyzed cascade annulation.
A facile and efficient copper-catalyzed cascade annulation of an imidazoheterocycle with salicylaldehyde, piperidine, and terminal alkyne was developed to afford unsymmetrical biheteroaryl derivatives. A variety of biheteroaryl structural motifs containing furans and imidazoheterocycles have been synthesized in ambient air in high yields. The experimental results suggest that the reaction proceeds through a sequential non-radical 5-exo-dig cyclization process.