Synthesis of a Novel Ring-Expanded Xanthine Analogue and Several Methyl or Benzyl Derivatives Containing the 5:7-Fused Imidazo [4,5-e][1,2,4]triazepine Ring System

Syntheses of 3,4,6,7-tetrahydroimidazo[4,5-e][1,2,4]triazepine-5,8-dione (1a) and its 3- and/or 7-methyl/benzyl substituted derivatives 1b-1e are reported. The structure of 1c is confirmed by single-crystal X-ray diffraction analyses