Robinson annelation under supercritical CO2 in the presence of various metal oxide catalysts without any organic solvent was studied to synthesize fused polycyclic compounds such as the series of steroid compounds. Under constant pressure and temperature, the reaction would have a limitation in the yield of desired product 8a-methyl-3,4,8,8a-tetrahydro-2H,7H-naphthalene-1,6-dione (5a) up to 57%. To improve the reaction yield of the product, we developed the new method that the pressure and temperature manipulation in one pot by using sub- and supercritical CO2 can be achieved successfully to obtain 5a in high yield (95%) and high selectivity (95%) without any modifications of the catalysts. This simple method could be applied for various ketones and various catalysts to synthesize fused polycyclic compounds.