Minute-scale, solvent-free microwave-assisted three-component synthesis of naphtho[1,2-e][1,3]oxazin-3-ones catalyzed by a recyclable Brønsted-Lewis acidic COF

We report a bifunctional Brønsted–Lewis acidic covalent organic framework catalyst, Cu(II)/TFPOTDB–SO 3 H, that enables the solvent-free, microwave-assisted three-component synthesis of naphtho[1,2-e][1,3]oxazin-3-ones from aromatic aldehydes, β-naphthol, and urea. Under optimized conditions (0.01 g catalyst, 180 W), a broad range of electron-donating and electron-withdrawing substituents delivers the target products in 93–99 % isolated yields within 2–4 min. The catalyst is demonstrably heterogeneous (hot-filtration test halts conversion) with negligible Cu leaching (≤ 0.05 ppm), maintains morphology and uniform Cu(II) distribution (∼ 6.6 wt%) as shown by SEM/EDS, and preserves high activity over five recycles. Compared with prior systems, Cu(II)/ TFPOTDB–SO 3 H offers markedly shorter reaction times at higher yields under greener conditions. A cooperative mechanism is proposed in which –SO 3 H groups protonate the carbonyl while Cu(II) coordination further polarizes it, accelerating C–N/C–O bond formation. Thus, the engineered sulfonated COF operates as a robust, recyclable designer catalyst, translating synergistic –SO 3 H/Cu(II) chemistry into minute-scale, high-yield synthesis of privileged 1,3-oxazine scaffolds.