Zn(L-proline)2 as an efficient and reusable catalyst for the multi-component synthesis of pyran-annulated heterocyclic compounds

We have developed a simple, straightforward and highly efficient multi-component one-pot synthesis of 2-amino-3-cyano-4H-pyrans and pyran-annulated heterocyclic compounds. Zn(L-proline)(2) has been utilized as a mild and efficient Lewis acid catalyst for the three-component reaction of aromatic aldehydes, malononitrile and enolizable C-H acids or activated phenols to synthesize pyran-annulated scaffolds. 3-Methyl-1-phenyl-2-pyrazolin-5-one, 4-hydroxycoumarine, dimedone, 4-hydroxy-6-methyl-2-pyrone, resorcinol, 1-naphthol and 2-naphthol were used as activated C-H acids. The products were isolated in high yields via vacuum filtration and without using any chromatography. The Zn(L-proline)(2) was recovered and reused in another reaction (three times) without significant loss of activity.