ABSTRACT

2-Chloro-4,5-dihydroimidazole 1a was first synthesised by Trani and Belassio in 1974 and since then has been widely used for the syntheses of various imidazoline- containing heterocyclic derivatives with interesting chemical and pharmacological properties.

The most important reactions of 1a consist in the displacement of chlorine atom with N-, O- or S- nucleophilic reagents leading to 2-substiuted imidazolines. Of special interest are the reactions with aromatic amines leading to 2-aryliminoimidazolidines 2-8 and Lewis acid-promoted reactions with azoles giving rise to the formation of N-(imidazolin-2-yl)-azoles 9 which act either as agonists or anatagonists of α-adrenergic and/or imidazoline receptors.

Reactions of 1a with N-arylhydroxylamines gave the corresponding N-aryl-N-(imidazolin-2-yl)-hydroxyl-amines 15 which serve as versatile substrates for the construction of polyhetero-Cope systems. Thus, the treatment of 15 with cyanogen bromide led to the formation of 3-(4,5-dihydroimidazol-2-yl)-2-oxo-2,3-dihydrobenzimidazole-1-carbonitriles 16, while the reaction with electron deficient acetylenes provided either 1-(4,5-dihydroimidazol-2-yl)indoles 21 or novel heterocyclic ketene aminals 22.

The compound 1a contains both the electrophilic centre at C-2 carbon atom and nucleophilic centre at N-3 nitrogen atom, and therefore, it is capable of undergoing a variety of multicomponent cyclocondensation reactions with azines, such as pyridine, isoquinoline and phthalazine, and with heterocumulenes such as carbon disulfide, isocyanates and isothiocyanates. Several fused heterocyclic systems 24, 28, 29, 35 and 37 thus obtained were further transformed into novel imidazoline-containing derivatives which would be difficult to synthesise on different way.