Biginelli three-component condensation of an aldehyde, β-keto ester, and urea proceeds smoothly on the surface of the silver salt of heteropolyacid (HPA), i.e. Ag 3 PW 12 O 40 , in water to afford the corresponding 3,4-dihydropyrimidinones in high-to-quantitative yields under mild conditions. The heterogeneous solid acid provides ease of separation of the catalyst and isolation of the products. The recovered catalyst can be recycled in subsequent reactions with consistent activity.
o-Phenylenediamines undergo smooth condensation with ketones having hydrogens at a-position on the surface of heteropoly acid (Ag 3 PW 12 O 40 ) under extremely mild conditions to afford the corresponding 1,5-benzodiazepines in excellent yields with high selectivity. The catalyst can be recovered by simple filteration and can be reused in subsequent reactions.
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