1. Synthesis of Biginelli dihydropyrimidinone derivatives with various substituents on aluminium-planted mesoporous silica catalyst
Hiroaki Murata, Haruro Ishitani, Masakazu Iwamoto Org Biomol Chem. 2010 Mar 7;8(5):1202-11. doi: 10.1039/b920821f. Epub 2010 Jan 13.
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.
2. A practical and green approach towards synthesis of dihydropyrimidinones: using heteropoly acids as efficient catalysts
Ezzat Rafiee, Hadi Jafari Bioorg Med Chem Lett. 2006 May 1;16(9):2463-6. doi: 10.1016/j.bmcl.2006.01.087. Epub 2006 Feb 7.
A simple and green chemistry procedure for the synthesis of dihydropyrimidinones using heteropoly acid mediated cyclocondensation reaction is described. This method provides an efficient and much improved modification of the original Biginelli reaction reported in 1893, in terms of high yields, and short reaction times. It has the ability to allow a wide variety of substitutions in all three components.
