A novel one-pot synthesis of spiro[indoline-3,4′-pyrazolo[3,4-e][1,4]thiazepine] diones using recyclable bioglycerol-based sulfonic acid functionalized carbon catalyst

A novel, simple, and efficient synthetic protocol has been developed for the synthesis of spiro[indoline-3,4′-pyrazolo[3,4-e][1,4]thiazepine] diones, by using bioglycerol-based sulfonic acid functionalized carbon as a recyclable catalyst, devoid of moisture sensitive metal catalysts and corrosive acidic reagents. This new protocol produces novel heptacyclic spirooxindole derivatives in good to excellent yields, with operational simplicity and recycling of the catalyst in comparison to predictable pentacyclic compounds. The catalyst can be prepared by a simple adoptable procedure from an inexpensive and readily available bio-glycerol and found to be recoverable and reusable up to four cycles without any loss of activity.