Imidazoles 2,4,5-triarylimidazoles synthesis

This transformation can also be carried out under solvent-free conditions in a domestic oven using acidic alumina and ammoniiun acetate, with or without a primary amine, to give 2,4,5-trisubstituted or 1,2,4,5-tetrasubstituted imidazoles, respectively (Scheme 15A) [69]. The automated microwave-assisted synthesis of a library of 2,4,5-triarylimidazoles from the corresponding keto-oxime has been carried out by irradiation at 200 ° C in acetic acid in the presence of ammonium acetate (Scheme 15B) [70]. Under these conditions, thermally induced in situ N - O reduction occurs upon microwave irradiation, to give a diverse set of trisubstituted imidazoles in moderate yield. Parallel synthesis of a 24-membered library of substituted 4(5)-sulfanyl-lff-imidazoles 40 has been achieved by adding an alkyl bromide and base to the reaction of a 2-oxo-thioacetamide, aldehyde and ammonium acetate (Scheme 15C) [71]. Under microwave-assisted conditions, library generation time was dramatically re-... 

There have been reports of a novel synthesis of 2,4,5-trialkyl-imidazoles by the rhodium-catalyzed reactions of alkenes with carbon monoxide and ammonia. Yields are 50-60%. Benzylamine and derivatives react with carbon tetrachloride in the presence of a catalytic amount of metal carbonyls to yield 2,4,5-triarylimidazoles and -imidazolines. The suggested reaction mechanism implicates an initially formed radical species which coordinates with the metal carbonyl. 

The structures of trisubstituted imidazoles are prevalent in natural products and pharmacologically active compounds, like the known P38 map kinase inhibitor and losartan. Besides, triarylimidazoles display various bioaclive effects such as herbi-cidal, fungicidal, analgesic, anti-inflammatory, and antithrombotic activities as well. The three-component synthesis of 2,4,5-trisubstituted imidazoles, a typical acid-catalyzed reaction, could be conducted successfully with good to excellent yields in a neutral ionic liquid, l-methyl-3-heptyl-imidazolium tetrafluoroborate ([Hemim] [BF ]), under solvent-free and microwave-assisted conditions (Fig. 12.46) [31],... 

Triaryl-substituted imidazoles were synthesized from benzil or benzoin, aldehyde, and ammonium acetate. A literature survey reveals several reports for the synthesis of triarylimidazoles using SSA as a catalyst. Shaabani et al. (2007) reported the synthesis of triarylimidazoles using SSA under conventional heating as well as microwave irradiation (Scheme 5.15). Microwave irradiation afforded the corresponding products in shorter reaction times (5-10 min). Catalytic reusability... 

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