Enviro-economic, facile, one-pot synthesis of novel spiro[pyrazolo [4,3-c] [1,5] benzothiazepines] using microwave irradiation

Abstract

An efficient method for the exclusive one-pot synthesis of novel pyrazolo [4,3-c][1,5]benzothiazepines (7a-e) possessing a spiro-3H-indoline nucleus is described. The investigation of the reaction between substituted o-aminothiophenols (5a-e) with 3-pyrazolidinyl-2H-indol-2one (3) to form the title products has been found interesting in view of the fact that different reaction sites are available in the key intermediate 3 which may lead to a mixture of products. Conventionally, 3 did not undergo reactions with 5a-e even under drastic conditions of prolonged reflux using strong acidic or basic catalysts in high boiling organic solvents for many days. However, the exclusive formation of the title products in a satisfactory yield (71 %) was achieved under microwave irradiation coupled with various inorganic supports indicative of a very strong specific microwave effect.