An efficient three-step synthesis of 5-substituted 2,3-dihydroimidazo [1,2-c]quinazolines and imidazo[1,2-c]quinazolines was elaborated. 2-(2-Aminophenyl)-4,5-dihydro-1H-imidazole, prepared by phosphorus pentasulfide catalyzed condensation of 2-aminobenzonitrile with ethylenediamine, smoothly reacted with aldehydes to give the corresponding 2,3,5,6-tetrahydroimidazo [1,2-c]quinazolines. The CH-NH fragments of the latter were subjected to selective oxidative dehydrogenation with one equivalent of potassium permanganate on silica gel to give 2,3-dihydroimidazo[1,2-c]quinazolines. With two equivalents of potassium permanganate on silica gel, a one-pot exhaustive dehydrogenation to imidazo[1,2-c]quinazolines was accomplished.Imidazo[1,2-c]quinazolines exhibit a tricyclic angularly fused ring system, which combines the biologically valuable imidazole and quinazoline moieties. Some representative examples substituted in the benzene ring 5-(2-oxoalkyl)-1a and a number of 5-(acylamino)-2,3-dihydroimidazo[1,2-c]quinazolines have been recently patented as potent anticancer agents. 1 Variously hydrogenated 5-alkyl-and 5-arylimidazo[1,2-c]quinazolines have shown a range of attractive pharmacological activity 2-8 and insecticidal properties. 9 Cyclometalated late-transitionmetal complexes (Ir or Pt) of imidazo[1,2-c]quinazolines have been patented as efficient dopants for organic electroluminescent layers in OLEDs. 10 However, in spite of significant interest in the field, there is still a shortage of mild and reliable synthetic methods for the preparation of selected imidazo[1,2-c]quinazoline derivatives. The reported methods are usually indirect, often require the use of drastic conditions, moisture-sensitive poisonous reagents, and/or poorly available precursors, which can limit the overall utility of the process. Currently, the most common approach to the synthesis of imidazo[1,2-c]quinazolines relies on a two-step assembly of the imidazole ring onto a quinazoline scaffold. 2a,3a,5a,11-15 For example, treatment of 4-chloroquinazolines with aziridines followed by I --catalyzed rearrangement of the isolated 4-(aziridin-1-yl)quinazoline intermediates gave the corresponding 2,3-dihydroimidazo[1,2-c]quinazolines in good yields. 5a,11,12 The latter compounds were also prepared by amination of 4-chloroquinazolines with chloroethylamine, 2a or through amination with aminoethanol followed by phosphoryl chloride or thionyl chloride induced ring closure. 3a,11,13 The reaction of 4-chloroquinazoline with aminoacetaldehyde dimethyl acetal followed by acid-catalyzed cyclization of the intermediate afforded the parent imidazo[1,2-c]quinazoline. 14 In a supplementary vein, condensation of 4-aminoquinazoline with bromoacetaldehyde provided an efficient formation of the imidazole ring to give the imidazo[1,2-c]quinazoline. 15 Some more complex transformations, which include the formation of both imidazole and quinazoline fragments of the imidazo[1,2-c]quinazoline system, have been also reported. 5b,16 Indeed, heating 2-substituted 4H-3,...
