Environmentally benign synthesis of 1,8-dioxooctahydroxanthene derivatives using 10-molybdo-2-vanadophosphoric acid as an efficient and reusable catalyst under solvent-free condition

A green and efficient protocol for the synthesis of 3,3,6,6-tetramethyl-9-aryl-1,8-dioxooctahydroxanthene derivatives via cyclocondensation of 5,5-dimethyl-1,3-cyclohexanedione and aromatic aldehydes in the presence of catalytic amount of 10- molybdo-2-vanadophosphoric acid under solvent-free conditions has been described. The 10-molybdo-2-vanadophosphoric acid was prepared and characterized by FT-IR spectroscopy, thermal analysis and XRD analysis techniques. Characterization of the catalyst by FT-IR spectroscopy confirms the substitution of two Mo^6+ ions by a V^5+ ion in a Keggin structure. The effect of various reaction parameters on the rate of reaction was investigated. The reaction was carried out without using any solvent and the process subscribes to the principles of green chemistry. Moreover, the present protocol offers several advantages such as simple work-up, shorter reaction time, excellent yields, recovery and reusability of catalyst.