Dihydroimidazole is a five-membered, nonplanar, and nonaromatic heterocycle, derived by the partial reduction of one of the two double bonds of the imidazole ring. The dihydroimidazoles are also referred to as imidazolines and there are three possible regioisomeric forms: 4,5-dihydroimidazole (2-imidazoline), 2,5-dihydroimidazole
(3-imidazoline), and 2,3- dihydroimidazole (4-imidazoline). The 2- and 3-imidazolines contain an imine center, while
4-imidazoline contains an alkene substructure. Among these three isomeric forms, the chemistry of 2-imidazoline is
more developed than 3- and 4-imidazolines.