Improved synthesis of 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) derivatives catalyzed by urea under ultrasound

Biginelli reactions were well catalyzed on mesoporous silica MCM-41 (M41) whose activity was much greater than that of amorphous silica. Octane was the most suitable among 6 kinds of solvents examined. The addition of metal ions on M41 enhanced the catalytic activity in the order Al > Ti > Fe = In. Al-planted M41s with Si/Al ratios of 45–35 showed the highest catalytic activity and could be used repeatedly though a small loss of the activity was observed. The catalysis could widely be applied to obtain various substituted dihydropyrimidinones (DHPMs) with high yields, some of which were very difficult to prepare until now. In addition, Biginelli reactions were combined with formyl C–H insertion reactions of diazoester on mesoporous silica; that is, a tandem one-pot four-component DHPM synthesis was attempted. Acetaldehyde, ethyl diazoacetate, p-tolualdehyde, and urea could be condensed and the corresponding DHPM derivative was obtained with 50% yield on Al-planted M41.

Synthesis of Biginelli dihydropyrimidinone derivatives with various substituents on aluminium-planted mesoporous silica catalyst

Applications of biological urea-based catalysts in chemical processes

Novel, Efficient, and Green Procedure for the Knoevenagel Condensation Catalyzed by Diammonium Hydrogen Phosphate in Water

Shaken not stirred: a facile synthesis of 1,4-bis(furo[2,3-d]-pyrimidine-2,4(1H,3H)-dione-5-yl)benzenes by one-pot reaction of isocyanides, N,N'-dimethylbarbituric acid, and terephthaldialdehyde.

An efficient and green procedure for the urea catalyzed Knoevenagel condensation was developed. In the presence of a catalytic ammount of urea, stoichiometric aldehyde and active methylene compound reacted under solvent-free conditions at 100 °C for 5-60 min to give nearly quantitative yield of product.

Shi Lan-Xiang

Papers

An Efficient and Green Procedure for the Knoevenagel Condensation Catalyzed by Urea