Synthesis of 2-substituted-4-methyl-5,13-dihydropyrimido[4′,5′:5,6][1,4]thiazepino[2,3-b]quinoxaline as a new heterocyclic system

2-Substituted-4-methyl-5,13-dihydropyrimido[4′,5′:5,6][1,4]thiazepino[2,3-b]quinoxalines (7a-g), derivatives of a new heterocyclic system were synthesized through cyclocondensation of 2,4-dichloro-5-(chloromethyl)-6-methylpyrimidine (3) with 3-aminoquinoxaline-2-thiol (4) and subsequent substitution by various secondary amines. Regioselective heterocyclization was confirmed by X-ray crystallographic analysis for 4-methyl-2-(pyrrolidin-1-yl)-5,13-dihydropyrimido[4′,5′:5,6] [1,4]thiazepino[2,3-b]quinoxaline (7a).