An efficient ZnO-catalyzed synthesis of novel indole-annulated thiopyrano-chromene derivatives via Domino Knoevenagel-hetero-Diels–Alder reaction

An efficient synthesis of pentacyclic indole derivatives is achieved via domino Knoevenagel-hetero-Diels–Alder reactions of indolin-2-thiones and O-propargylated salicylaldehyde derivatives in CH3CN in the presence of 10 mol % of ZnO as a heterogeneous catalyst. The products are formed in good to excellent yields.