The copper-promoted cycloaddition between nitrogen heterocyclic compounds (pyridine-2-carbonitrile, 2-pyridylacetonitrile and isoquinoline-3-carbonitrile) and ketones (acetone, pentan-2-one and pentan-3-one) has been studied, and a mechanism proposed on the basis of single crystal X-ray analysis, and H-1 NMR and IR spectra of intermediate products.