Microwave-assisted synthesis of substituted imidazoles on a solid support under solvent-free conditions

Usyatinsky, Alexander; Khmelnitsky, Yuri L.

doi:10.1016/s0040-4039(00)00771-1

Cited by 194 publications

(84 citation statements)

References 11 publications

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“…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.…”

Section: Resultsmentioning

confidence: 99%

“…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.…”

Section: Resultsmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

“…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. …”

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confidence: 99%

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

Silva¹,

Silva²,

Ferreira³

et al. 2008

J. Braz. Chem. Soc.

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Naftoimidazóis inéditos foram preparados por reação, ativada por microondas, entre paraformaldeído, β-lapachona (ou o-quinonas correlatas) e acetato de amônio suportado em montmorilonita k-10, ou em alumina básica. O uso do suporte básico forneceu os melhores rendimentos, superiores a 80%. Isso foi confirmado para a reação com β-lapachona e piperonal.New naphthoimidazoles were prepared by reaction, activated by microwave irradiation, between paraformaldehyde, β-lapachone (or related o-quinones) and ammonium acetate supported on montmorillonite k-10, or on basic alumina. Use of the basic support gave the best results, with yields above 80%. This was confirmed for the reaction with β-lapachone and piperonal.Keywords: imidazole, microwave, basic alumina, lapachone Introduction β-Lapachone (1a) is an ortho-naphthoquinone present in small amounts in trees of the Tabebuia species (Bignoniaceae), commonly called "ipê" or "pau d'arco" in Brazil. In addition, it can be obtained by the isomerization of lapachol, a quinone that is more abundant and more readily extracted from the same sources. The biological activities of these compounds and simple derivatives, have been investigated since the 1940's (anti-malarial 1 ) up to the present (anti-tumor, 2 anti-microbial, 3 anti-inflammatory 4 and anti-parasitic 5 ) and were recently reviewed. 6 The use of β-lapachone and some semi-synthetic derivatives as chemotherapic agents in the treatment of American trypanosomiasis (Chagas disease) has been investigated, 7 and five imidazole derivatives, prepared from this quinone and aromatic aldehydes, have shown expressive action over the tripamastigote form of Trypanosoma cruzi. 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. Results and DiscussionImidazole synthesis from α-diketones has a long history 16 and was initially plagued by low yields and by-products (such as oxazoles). Improvements occurred by the use of acidic conditions, e.g., glacial acetic acid reflux. 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, 11-13 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.Based on these findings, th...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

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

Silva¹,

Silva²,

Ferreira³

et al. 2008

J. Braz. Chem. Soc.

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“…One of the first examples of parallel processing using 96-well plates was carried out by Cotterill et al (1998), who presented microwave-assisted parallel synthesis of pyridine libraries. Following this study, various studies (Kappe, Kumar, & Varma, 1999;Usyatinsky & Khmelnitsky, 2000;Olsson, Hansen, & Andersson, 2000) have proposed multi-component strategies to synthesize heterocyclic components.…”

Section: Parallel Processing In Microwave Reactorsmentioning

confidence: 99%

Microwave Assisted Reactions in Organic Chemistry: A Review of Recent Advances

Jacob¹

2012

IJC

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Revolution in organic compound synthesis has been promoted by microwave assisted organic syntheses (MAOS) by which small molecules are built up into large polymers in a fraction of time. The need for different organic compound libraries for drug discovery, biomaterial development, automated library screening; proteomics etc has supported the emergence of innovative technologies for rapid combinatorial organic synthesis using MAOS synthesis. In previous reviews on this subject the focus of MAOS has been on the process of MAOS reactions rather than the importance given to the related applications. This review focuses on solid-phase synthesis, biopolymer synthesis, applications in proteomics, parallel processing in microwave reactors and automated library generation by means of sequential microwave irradiation methods. This article has discussed the different applications of Microwave assisted synthesis of organic polymeric compounds most thoroughly by focusing on aspects of speed, reproducibility and scalability. From this review it is clearly identified that independent on the type of organic material, data consistently points out to MW as a novel and powerful tool which has enable synthesis of a number of new compounds and presents the need for future research in this area.

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Microwave Technology—Chemical Synthesis Applications

Varma¹

2003

Kirk-Othmer Encyclopedia of Chemical Technology

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Microwave‐accelerated chemical syntheses in various solvents as well as under solvent‐free conditions have witnessed an explosive growth. This technology, which is still in its growth phase, has found widespread application predominantly exploiting the inexpensive unmodified household microwave (MW) ovens although the use of dedicated MW equipment has been rapidly gaining ground. Of special interest is the environmentally friendlier solventless approach that often involves exposure of neat reactants to MW irradiation or employs supported reagents on recyclable inorganic oxides or catalysts and has been adequately demonstrated in several MW‐assisted condensation, deprotection, rearrangement, cyclization, reduction, and oxidation reactions. The rapid one‐pot preparation of heterocyclic compounds from in situ generated reactive intermediates and the general application to multicomponent reactions, that are adaptable for building a library of compounds, have been accomplished using this MW technique. More recently, the strategy has been extended to combinatorial chemistry and the synthesis of a newer class of solvents, ionic liquids that are essentially molten salts with barely measurable vapor pressure. The salient features of these high yield protocols, namely, the selectivity, experimental ease of manipulation, and the enhanced reaction rates are discussed.

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Microwave-assisted synthesis of substituted imidazoles on a solid support under solvent-free conditions

Cited by 194 publications

References 11 publications

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

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

Microwave Assisted Reactions in Organic Chemistry: A Review of Recent Advances

Microwave Technology—Chemical Synthesis Applications

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