Synthesis of 3,4-dihydropyrimidin-2(1H)-ones catalyzed by poly(ferric 2-acrylamido-2-methylpropanesulfonate)

Poly(ferric 2-acrylamido-2-methylpropanesulfonate) (PFAMPS) was prepared via the reaction of poly(2-acrylamido-2-methylpropanesulfonic acid) and Fe(OH)3. PFAMPS was used as a heterogeneous catalyst for the Biginelli reaction of aldehyde, ethyl acetoacetate, and urea to synthesize 3,4-dihydropyrimidin-2(1H)-ones with yields of 70–87%. PFAMPS can be recycled six times without significant loss in catalytic activity. For comparison, ferric lignosulfonate (FLSA), ferric cellulose sulfonate (FCSA), ferric starch sulfonate (FSSA), and ferric 732 cation exchange resin (FACER) were used as catalysts of the Biginelli reaction. It was shown that the catalytic activities of recycled FLSA, FCSA, FSSA, and FACER significantly decreased after two reactions. Fe3+ in the polymer sulfonates acted as the catalyst for the Biginelli reaction. PFAMPS was the chelate, where the action between Fe3+ and the poly(2-acrylamido-2-methylpropanesulfonate) matrix was strong, and Fe3+ lost little from the PFAMPS. However, significant Fe3+ loss was observed in the FLSA, FCSA, FSSA and FACER polymer matrices after reuse.