Microwave-Assisted K-10 Montmorillonite Clay-Mediated Knoevenagel Hetero-Diels-Alder Reactions: A Novel Protocol for the Synthesis of Polycyclic Pyrano[2,3,4-kl]xanthene Derivatives

The intramolecular hetero-Diels-Alder reactions of 2-(cyclohex-2-enyloxy)benzaldehyde by Knoevenagel condensation with symmetrical 1,3-diones under three different conditions afforded the pyrano[2,3,4-kl]xanthene derivatives in a stereoselective manner in good yield. The structure of one of the products was unambiguously established by x-ray analysis.