Facile synthesis of 6-aryl-1,3-dimethyl-5H-pyrimido[4,5-b][1,4]diazepine-2,4(1H,3H)-diones

A facile procedure for the preparation of 6-aryl-1,3-dimethyl-5H-pyrimido [ 4,5-b] [1,4]diazepine2,4(1H,3H)-diones 8, 9 from 6-amino-5-arylideneamino-1 ,3-dimethyluracils 1, 2 and triethyl orthoacetate (3) in a two-step reactio n via 6-aryl-8-ethoxy-6,7-dihydro-1,3-dimethyl 5H-pyrimido[4,5-b] [1,4] dia zepine-2,4(1H,3H)-diones 6, 7 is described. Condensation of 1 with diethoxy methyl acetate (10) resulted in the formation of (1,3-dimethyl-2,6-(1H,3H)d ioxopurin-7-yl)(phenyl)methyl acetate (11) and a small amount of 1,3-dimelh yl-6-phenyl pyrazino [2,3-d]pyrimidine-2,4(1H,3H)-dione (12). The structure s of 6 and 11 were unambiguously confirmed by single-crystal X-ray diffract ion analysis.