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-formyl­ation of 8,9,10,11-tetra­hydro­pyrido[2′,3′:4,5]pyrimido[1,2-a]-azepin-5(7H)-one has been studied for the first time. It was revealed that formyl­ation proceeds by the formation of an inter­mediate salt, which due to the re-amination process on treatment with aqueous ammonia transformed into the corresponding (E)-11-(amino­methyl­ene)-8,9,10,11-tetra­hydro­pyrido[2′,3′:4,5]-pyrimido[1,2-a]azepin-5(7H)-one, C13H14N4O, as an E-isomer. Formyl­ation 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 mol­ecule, the seven-membered penta­methyl­ene ring adopts a twist-boat conformation.