ABSTRACT
Microwave-assisted solvent-free synthesis of 1,2,4,5-substituted and 2,4,5-substituted imidazoles has often been reported. Imidazoles can be obtained by condensation of a 1,2-dicarbonyl compound with an amine and an aldehyde using acidic alumina impregnated with ammonium acetate as the solid support. Benzimidazole is an important heterocycle known for its pharmacological activities and synthetic utility. It is used in a number of ways —as an anti-helminthic, anti-fungal, anti-histaminic, anti-HIV, anti-hypertensive, anti-ulcer, neuroleptic and cardiotonic. Pyrazolo[3,4-b]pyridines are an important class of heterocycles exhibiting a wide range of bioactivities and are structural analogs of purine bases. Although amides, amines, azoles or hydrazines are used as nitrogen sources in most copper-catalyzed cascade reactions involving carbon-nitrogen coupling, some unconventional N-possessing moieties like amidines also act as nitrogen sources to afford several heterocyclic functionalities by copper-catalyzed transformation. The synthesis of five-membered N-heterocycles like imidazoline and oxazoline has drawn the attention of researchers due to their wide application in the preparation of pharmacologically active compounds.
