Zeolite supported Brønsted-acid ionic liquids: an eco approach for synthesis of spiro[indole-pyrido[3,2-e]thiazine] in water under ultrasonication

A zeolite supported Brønsted-acid catalyst system has been developed using different Brønsted-acid ionic liquids supported on ZSM-5 zeolite. Catalytic activity was tested via aqueous-mediated ultrasound-promoted synthesis of novel N -substituted spiro heterocycles, which does not take place under conventional conditions. The yield of the desired products was increased in the presence of ultrasonication compared to those of conventional and MW techniques. In the presence of ultrasonication, the recyclability of this novel catalyst system was studied. There was no loss of catalytic activity up to five cycles whereas a significant loss was observed in the presence of MWs. Ultrasound-promoted novel protocol has been developed for spiro heterocycles. Those reluctant to be formed under conventional conditions, can be prepared by one pot cyclocondensation reaction between N -substituted isatin and amines with 2-mercaptonicotinic acid in the presence of a novel ZSM-5-zeolite Brønsted-acid catalyst system in water.