One-pot efficient green synthesis of spirooxindole-annulated thiopyran derivatives via Knoevenagel condensation followed by Michael addition

A green, operationally simple and highly efficient one-pot three-component approach for the synthesis of spiro[indoline-3,4′-thiopyrano[2,3-b]indole] derivatives has been developed by the domino reaction of indoline-2-thione, isatin and ethyl cyanoacetate or malononitrile in ethanol at 80 °C for just 20 min. The significant advantages of this protocol are short reaction time, excellent yields, operational simplicity and formation of three new bonds in one operation from easily available starting materials.