ORGN 746 |
| The initial synthesis of dihydropyrimidone following Biginelli condensation has proved to be inefficient with 20-50% yield. Better methods have been discovered, but through multiple sequences and hazardous conditions. A few other attractive methods are known, but most of them employ anhydrous reaction conditions and Lewis acids (BF3.Et2O, LiClO4, InCl3, ZrCl4, NiCl2.6H2O, BiCl3, Bi(OTf)3, and FeCl3). Therefore, development of an efficient and operationally simple catalytic method is necessary for the synthesis of this type of multifunctionalized rings. In a series of publications, we have demonstrated the versatility and usefulness of bismuth nitrate-catalyzed organic reactions. We report here bismuth nitrate-induced synthesis of dihydropyrimidone. This method has been successfully applied with a number of substrates and results in excellent yield of the products. In contrast to the existing mechanism of this reaction, a different mechanism has been advanced. In contrast to the existing method, no acylimine has been formed. We propose that the b-keto ester undergoes condensation and subsequent dehydration with carbonyl compounds in the presence of bismuth nitrate. The unstaturated keto compound then undergoes Michael-type of reaction with urea/thiourea. A co-ordination of bismuth to the b-keto ester has been noted in nmr through a chemical shift difference. |
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Combinatorial, Parallel and Process Chemistry, Heterocycles, Aromatics, New Reactions and Methodology
8:00 PM-10:00 PM, Wednesday, August 22, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Organic Chemistry |