Efficient synthesis of spiro compounds using water extract of banana peel ash (WEBPA) under sonication

In this article, we have described an eco-friendly and sustainable new approach for the synthesis of spiro[indoline-3,4′-pyrano[4,3-b]pyran] derivatives utilizing waste-originated water extract of banana peel ash (WEBPA) <i>via</i> a three component reaction of substituted isatins, malononitrile/ethylcyanoacetate and 4-hydroxy-6-methyl-2<i>H</i>-pyran-2-one. The present multicomponent reaction has been carried out in WEBPA under ultrasound irradiations without using any external catalyst and volatile organic solvents and the desired compounds were obtained in good yields in shorter reaction time. We expect that the method outlined here will prove highly valuable in synthetic chemistry and the production of other heterocyclic compounds in the near future.