General procedure for the synthesis of 1-benzyl-1,4-diazepan-5-one from N-benzylpiperidone: [Ref. Example 119]; 1-benzylhexahydro-1H-1,4-diazepan-5-one; [] Concentrated sulfuric acid (25 mL) was slowly added dropwise to a solution of acetic acid (50 mL) of 1-benzyl-4-piperidone (10.14 g) at room temperature followed by a batch at 0 °C Sodium azide (3.880 g) was added. The reaction was carried out at 0 °C for 2 h, followed by warming to 5 °C and stirring for 25 h. The reaction was completed with the addition of sodium hydroxide (3.880 g). Upon completion of the reaction, the reaction mixture was adjusted to alkaline with aqueous sodium hydroxide solution followed by liquid-liquid partition extraction with chloroform. The aqueous layer was further extracted with chloroform. All organic layers were combined, washed with saturated brine, dried over anhydrous sodium sulfate and filtered. The solvent was removed by concentration under reduced pressure and the residue was purified by silica gel column chromatography (eluent: chloroform-methanol gradient) to afford 1-benzyl-1,4-diazepan-5-one as a white solid (5.081 g, 47% yield).1H-NMR (400 MHz, CDCl3) δ: 2.50-2.70 (6H, m), 3.20-3.35 (2H, m) , 3.60 (2H, s), 6.07 (1H, br), 7.20-7.40 (5H, m).MS (ESI) m/z: 205 (M + H)+.
