Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5221775 | Tetrahedron | 2010 | 9 Pages |
For the first time hexaaquaaluminium(III) tetrafluoroborate has been used as a mild acid catalyst in organic synthesis. A simple method of its preparation based on the reaction of aluminium triisopropoxide and tetrafluoroboric acid in isopropanol afforded catalyst of high purity and activity. The three-component Biginelli condensation of acetoacetate esters, urea and aldehydes catalyzed by 10 mol % of [Al(H2O)6](BF4)3 in refluxing acetonitrile afforded 3,4-dihydropyrimidonones in good to high yields on multigram scales. The tolerance to acid sensitive reactants such as thienyl and furyl carbaldehydes, applicability to sterically hindered β-ketoesters and simple recyclability without losing catalytic activity make this catalyst as good replacement to literature methods. The mechanism of the reaction includes formation of the so called 'ureido-crotonate' rather than corresponding acylimino intermediate as found with Brønsted type catalysts.
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