PPA-SiO2 catalyzed solvent-free synthesis of some novel 4,6-diaryl-2,3a,4,5-tetrahydro-3H-indazol-3-ones from 3,5-diaryl-6-carbethoxy cyclohexenones

A simple, efficient and green method for the synthesis of 4,6-diaryl-2,3a,4,5-tetrahydro-3H-indazol-3-ones has been described using 3,5-diaryl-6-carbethoxy cyclohexenones in the presence of silica gel-supported polyphosphoric acid, an effective and reusable catalyst, under solvent-free conditions. The starting 3,5-diaryl-6-carbethoxy cyclohexenones have been synthesized by the Michael addition of chalcones and ethylacetoacetate followed by internal Claisen condensation using K2CO3 in solvent-free conditions. The present methodology offers several advantages, such as short reaction time, high yield, and the absence of volatile and hazardous organic solvents. Structural assignments are based on H-1, C-13 NMR, FTIR, and C, H, N analysis.