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

Abstract

An alternate approach to 2-(substituted phenyl)-3,3a-dihydro-8H-pyrazolo[5,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-pyrazolo[5,1-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.

GRAPHICAL ABSTRACT

Keywords:

• Chalcone N-formyl-2-pyrazoline
• Friedel–Crafts acylation
• 2-(substituted phenyl)-3,3a-dihydro-8H-pyrazolo[5,l-a]isoindol-8-ones

ACKNOWLEDGMENTS

This work was financially supported by the Indian Institute of Technology Roorkee through Ministry of Human Resource Development (MHRD), New Delhi. D. D. thanks MHRD for the award of fellowship.

Notes

^a All reactions were carried out according to the general procedure.

^b Yields refer to isolated products.