One-pot, solvent-free synthesis via Biginelli reaction: Catalyst-free and new recyclable catalysts

Free catalyst one-pot three components coupling of aldehydes, β-dicarbonyl compounds, and urea was performed to afford both the corresponding 3,4-dihydropyrimidine-2-ones (DHPOs, (1–9)a) and their sulfur analogs 3,4-dihydropyrimidine-2-thiones (DHPTs, (1–9)b), synthesized in the presence of uranyl acetate (UA) and succinimide sulfonic acid (SuSA) as catalysts under the same conditions via Biginelli condensation protocol. Interestingly, the free catalyst reactions were performed for 4 h for DHPOs with the yields of high to excellent, while in the cases of DHPTs, the yield was lower. But when the UA or SuSA was used, the yields (both of DHPOs and DHPTs) were high to excellent and the reaction times were either 2.5 or 1 h, respectively. Also, these two catalysts were recyclable for four consecutive runs.