Unusual formation of (E)-11-(amino-methyl-ene)-8,9,10,11-tetra-hydro-pyrido[2',3':4,5]pyrimido[1,2-a]azepin-5(7H)-one and its crystal structure.

Selective C-formyl-ation of 8,9,10,11-tetra-hydro-pyrido[2',3':4,5]pyrimido[1,2-a]-azepin-5(7H)-one has been studied for the first time. It was revealed that formyl-ation proceeds by the formation of an inter-mediate salt, which due to the re-amination process on treatment with aqueous ammonia transformed into the corresponding (E)-11-(amino-methyl-ene)-8,9,10,11-tetra-hydro-pyrido[2',3':4,5]-pyrimido[1,2-a]azepin-5(7H)-one, C13H14N4O, as an E-isomer. Formyl-ation was carried out by Vilsmeier-Haack reagent and the structure of the synthesized compound was confirmed by X-ray structural analysis, spectroscopic and LC-MS methods. In the mol-ecule, the seven-membered penta-methyl-ene ring adopts a twist-boat conformation.