Catalytic conjugate addition of heterocyclic compounds to α,β-unsaturated carbonyl compounds by hafnium salts and scandium salts

The hafnium chloride (HfCl4) and scandium chloride (ScCl3) catalyzed conjugate additions of heterocyclic compounds, such as indoles, pyrrole, pyrazole, and imidazole, have been demonstrated. Hafnium chloride effectively catalyzed the conjugate addition of indoles to α,β-unsaturated carbonyl compounds, and the addition product was obtained in high yield. The reaction of pyrrole was also catalyzed by HfCl4 or ScCl3, and produced 2,6-dialkylated pyrroles up to 99% yields. Furthermore, the conjugate addition of the 1-position of the pyrazoles and imidazole occurred, and produced several substituted heterocyclic compounds in good yields.