One-pot synthesis of tetrasubstituted imidazoles catalyzed by zeolite HY and silica gel under microwave irradiation

Abstract

Four-component condensation of benzil, aromatic aldehydes, primary amines and ammonium acetate catalyzed by zeolite HY and silica gel without any solvent under microwave irradiation leads to tetrasubstituted imidazoles in high yields and purity.

Synthesis of imidazole derivatives from β-lapachone and related compounds using microwave and supported reagents

“…17 The availability of microwave technology for synthetic purposes has allowed the efficient preparation of 2,4,5-trissubstituted and 1,2,4,5-tetrassubstituted imidazoles. Further observed benefits, that were occasionally associated with solid supports such as silica, alumina, clays, amongst others, [11][12][13] included improved yields, and dramatic reductions in reaction time and quantities of solvent used (AcOH). 14,15 Interestingly, the best supports found in these studies were always the acidic in nature.…”

“…The low yields for 3 and 4 are in accordance with literature data, where acidic conditions afforded better results. [11][12][13]17 In addition, it was also investigated whether these reactions could occur efficiently without a support or microwave energy (other conditions kept equal). The experiments were carried out for the synthesis of compound 2a.…”

“…Microwave activation has provided significant improvement on heterocyclic synthesis, 10 including imidazoles, with [11][12][13] or without support, 14,15 with reduction/ elimination of solvents, decreased reaction times and equal or improved yields.…”

“…8,9 These imidazole derivatives were prepared by conventional methods. 9 As part of an ongoing study into the use of microwave activation and the use of supported reagents, in this case ammonium acetate, we investigated the preparation of the previously unknown simple imidazole derivatives of β-lapachone and related ortho-quinones with formaldehyde.Microwave activation has provided significant improvement on heterocyclic synthesis, 10 including imidazoles, with [11][12][13] or without support, 14,15 with reduction/ elimination of solvents, decreased reaction times and equal or improved yields. …”

Arylazoazines and arylazoazoles as interesting disperse dyes: Recent developments with emphasis on our contribution laboratory outcomes

“…Another efficient method is heating cyanoacetamide and methyl acetoacetate in a microwave oven [41]. Balalaie et al [42][43][44][45][46][47][48] have reported an efficient three component condensation of alkyl cyanoacetates, primary amines, and β-ketoesters with higher yields on the surface of silica gel, montmorillonite K-10, zeolite, and acidic alumina under microwave irradiation, the obtained products 19a-h in yields ranging from 91 to 93%. These compounds have two tautomeric forms, and in solution there is a very fast equilibration between them [49].…”