Alternate Synthesis Route of 2-(Substituted Phenyl)-3,3a-dihydro-8H-pyrazolo[5,1-a]isoindol-8-ones via Chalcone-Based N-Formyl-pyrazolines

An alternate approach to 2-(substituted phenyl)-3,3a-dihydro-8H-pyrazolo5,l-a] isoindol-8-ones via chalcone-based N-formyl-pyrazolines is described. N-Formyl-pyrazolines were prepared in excellent yield (81–96%) by the reaction of chalcones with hydrazine hydrate in the presence of formic acid, which undergoes intramolecular Friedel–Crafts acylation in the presence of trifluoroacetic acid (TFA) as a catalyst to afford functionalized 2-(substituted phenyl)-3,3a-dihydro-8H-pyrazolo5,1-a]isoindol-8-ones in good to excellent yield (74–94%) at reflux in acetonitrile. Our synthetic route avoids expensive reagents and significantly improves yields.