Density functional theory approach was used for the 4-methyl-2,3-dihydro-1,5-benzodiazepin-2-one compound to determine the mechanism of hydrazinolysis of 4-substituted 2,3-dihydro-1,5-benzodiazepin-2-ones. Single point computations at the MP2/6-311+G(d,p)//B3LYP/6-31G(d) level were performed for the more precise energy prediction. The solvent effect was taken into account by carrying out single point calculations using the PCM methodology. The obtained results show that in the investigating mechanism the first step consists of the hydrazine molecule addition to the azomethine bond of the 4-methyl-2,3-dihydro-1,5-benzodiazepin-2-one. Further cyclization occurs with pyrazole ring formation, and then the diazepine ring opening is revealed. Finally, removal of o-phenylendiamine leads to 3-methylpyrazolone-5 as a main product that is in agreement with the experimental observation. The final step is a rate-determining step of this reaction.

Density functional theory approach was used for the 4-phenyl-2,3-dihydro-1,5-benzodiazepine-2-thione compound to determine the mechanism of hydrazinolysis of 4-substituted 2,3-dihydro-1,5-benzodiazepine-2-thiones. Single-point calculations at the MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) level were performed for the more accurate energy prediction. The solvent effect was taken into account by carrying out single-point calculations using the PCM methodology. The obtained results show that in the investigating mechanism the first step consists of the hydrazine molecule addition to the thiocarbonyl bond of the 4-phenyl-2,3-dihydro-1,5-benzodiazepine-2-thione following removal of H(2)S. Further addition of another hydrazine molecule to the azomethyne bond and cyclization with pyrazole ring formation occur, and then the diazepine ring-opening and the removal of hydrazine molecule proceed. Finally, imine-enamine tautomerization leads to 5-N-(2-aminophenyl-1-amino)-3-phenylpyrazole as a main product that is in agreement with the experimental observation. The cyclization step is a rate-determining step of this reaction.