Derivatives of 1,4-benzodiazepine have found wide application in medical practice as anxiolytics, hypnotics and myorelaxant agents. Introduction of alkyl substituent and, subsequently, hydroxy group to position 3 will allow to obtain chiral derivatives less susceptible to racemization. We have carried out the synthesis of 7-bromo-3-methyl-1,2-dihydro-3H-1,4-benzodiazepine-2-one (1), then by its oxidation we have obtained 4-oxide-7-bromo-3-methyl-1,2-dihydro-3H-1,4-benzodiazepine- 2-one (2) which has been subjected to Polanovsky rearrangement by action of acetic anhydride to give 7-bromo-3-acethoxy-3-methyl-1,2-dihydro-3H-1,4-benzodiazepine-2-one (3). H2O2, AcOH (Ac)2O N H N CH3 O Br N H N + CH3 O Br O N H N O O Br CH3 CH3 O 1 2 3 Structures of compounds 1-3 were confirmed by mass and PMR spectroscopy, as well as by single crystal X-ray analysis. Compound 1 crystallizes as a hydrobromide salt, 1.HBr in the form of centrosymmetric dimers through the N-H···Br hydrogen bonds, N...Br 3.359(4) and 3.252(4) Å, angles NHBr 172(5) and 164(4) º (Figure, left). Two crystallographically independent molecules 2 present in the asymmetric unit in S and R configurations and alternate in the H-bonded chain via NH...O hydrogen bonds, N...O 2.844(4) and 2.893(4) Å, angles NHO 160(4) and 165(4) º. Neutral molecules 3 form the centrosymmetric dimers via R2 2(8) amide homosynthon, N...O 2.891(3) Å, angle NHO 172(3) º (Figure, right).