Synthesis of novel spiro[chromeno[2,3-d][1,3,4]thiadiazolo[3,2-a] pyrimidines via an isatin-based three-component reaction.

This study presents an efficient and sustainable method for the synthesis of novel spiro[chromeno[2,3-d][1,3,4]thiadiazolo[3,2-a]pyrimidine-10,3'-indoline]-2',9,11-trione derivatives via a three-component condensation reaction is introduced. The reaction involves dimedone, 5H-[1,3,4]thiadiazolo[3,2-a]pyrimidine-5,7(6 H)-dione, and isatin derivatives, catalyzed by the economical and highly effective Keggin heteropolyacid (H₃PW₁₂O₄₀). This protocol achieves (70-90%) yields within relatively short reaction times under mild and solvent-free conditions. Using a green, cost-effective catalyst highlights the method's practicality and potential for broader applications in synthetic organic chemistry, offering an attractive route for spiro oxindole derivative synthesis.