A novel series of spiroheterocycles was synthesized via a one-pot, three-component reaction of 4-benzo[h]quinolin-2(1H)-one, malononitrile dimer, and various isatin derivatives. The process, catalyzed by DABCO in refluxing ethanol, demonstrated broad substrate tolerance towards substituted and N-alkylated isatins, yielding ten novel heteropolycyclic compounds in good to excellent yields. The structures of products were characterized using ¹H NMR, ¹³C NMR, FT-IR, mass spectrometry, and elemental analysis. The definitive structure of a representative compound was established using HSQC, HMBC, and X-ray diffraction analysis. The protocol’s simplicity, high efficiency, and green credentials underscore its potential for constructing complex spiroframeworks in synthetic and medicinal chemistry.

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