Abstract
An efficient synthesis of novel 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) and their derivatives, using Brønsted acidic ionic liquid [C2O2BBTA][TFA] as a catalyst, from the condensation of aryl aldehyde, β-ketoester and urea was described. Reactions proceeded smoothly for 40 min under solvent-free conditions and gave the desirable products with good to excellent yields (up to 99%). The catalyst could be easily recycled and reused with similar efficacies for at least six cycles.
Highlights
In recent years, 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) and their derivatives have received much attention because they are important substructures in both biologically active compounds and several marine alkaloids involving the DHPM core units [1]
A simple and direct approach for their synthesis involves the conjugate addition of aryl aldehyde, β-ketoester and urea in the presence of either protic or Lewis acids
Several improved methods have been reported for the preparation of these compounds using various catalysts such as p-TsOH H2 O [2], H3 BO3 [3], [Al(H2 O)6 ](BF4 )3 [4], thiamine hydrochloride [5], L-(+)-tartaric acid-dimethylurea [6], imidazole-1–yl-acetic acid [7], HClO4 -SiO2 [8], polyvinylsulfonic acid [9], SnCl2 ̈ 2H2 O [10], NaCl [11], SrCl2 ̈ 6H2 O [12], Al-planted MCM-41 [13], (NH4 )2 CO3 [14], CeCl3 ̈ 7H2 O [15], CaCl2 [16], Ce(NH4 )2 (NO3 )6 [17] and Fe(OTs)3 ̈ 6H2 O [18]
Summary
3,4-dihydropyrimidin-2(1H)-ones (DHPMs) and their derivatives have received much attention because they are important substructures in both biologically active compounds and several marine alkaloids involving the DHPM core units [1]. Several improved methods have been reported for the preparation of these compounds using various catalysts such as p-TsOH H2 O [2], H3 BO3 [3], [Al(H2 O)6 ](BF4 )3 [4], thiamine hydrochloride [5], L-(+)-tartaric acid-dimethylurea [6], imidazole-1–yl-acetic acid [7], HClO4 -SiO2 [8], polyvinylsulfonic acid [9], SnCl2 ̈ 2H2 O [10], NaCl [11], SrCl2 ̈ 6H2 O [12], Al-planted MCM-41 [13], (NH4 ) CO3 [14], CeCl3 ̈ 7H2 O [15], CaCl2 [16], Ce(NH4 ) (NO3 )6 [17] and Fe(OTs)3 ̈ 6H2 O [18] Several of these reported procedures suffer from some drawbacks such as strong acidic conditions, long reaction times, use of expensive or hazardous reagents, complex handling and low yields of products. New, efficient and environmentally friendly procedures are still strongly demanded in organic transformations such as condensation reactions
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