12 novel substituted 3,4-diethoxycarbonyl-2-(thiazol-2-yl)benzo[b] [1,4]diazepines were obtained via a domino sequence of a nucleophilic addition/dehydration/cyclization/H⁺ shift. These reactions were achieved by reacting substituted 1,2-phenylenediamines, 2-thiazolecarboxaldehyde with diethyl acetylenedicarboxylate in EtOH. Benzo[b]-[1,4]diazepines of the two structures of imine structure and enamine structure were found in this reaction process due to chem-/regio-selectivity. The influence of reaction conditions on the selectivity of target products was also studied in detail. The selectivity law of synthesis reaction was obtained, and the yield of single product was maximized. A simple synthesis strategy for the selective synthesis of benzo[b] [1,4]diazepines was provided. To understand the reaction mechanism and further prove the conclusion, quantum chemical calculations were performed, and density functional theory (DFT) studies based on B3LYP method and 6-31G basis set were employed to carry out the study. Natural bond orbital (NBO) charge analysis of the substituted 1,2-phenylenediamine was carried out to justify the selective attack at the nucleophilic centers. NBO charge analysis of the target compounds was carried out to explain the stability of benzo[b] [1,4]diazepine isomers with imine or enamine structure. Moreover, the plausible reaction mechanism was proposed.

Key words: benzo[b] [1,4]diazepine, synthesis, selectivity, mechanism, density functional theory (DFT)