2-Chloro-3,4-dihydroimidazole. Part 2. Synthesis of cyanines from 6-aryl-2,3-dihydro-6aH-imidazo[1,2-a]pyrido[1,2-c][1.3.5]triazin-5(6H)-ones. Crystal and molecular structure of 6-phenyl-2,3-dihydro-6aH-imidazo[1,2-a]pyrido[1,2-c][1,3,5]triazin-5(6H)-one

2-Chloro-3,4-dihydroimidazole (1) reacts with pyridine and aromatic isocyanates to give 6-aryl-2,3-dihydro-6aH-imidazo[1.2-a]pyrido[1,2-c][1,3,5]triazin-5(6H)-ones (5a–g). The crystal and molecular structure of 6-phenyl-2,3-dihydro-6aH-imidazo[1,2-a]pyrido[1,2-c][1,3,5]triazin-5(6H)-one (5a) determined from X-ray diffraction data is presented. Reaction of the compounds (5a–f) with malononitrile provides a new route to the cyanines (8a–f).