The mixture of 350 mg (2.2 mmol) of 2- azidobenzoic acid in 12 mL of acetonitrile and 30 mL of water was irradiated for 24 h. The reaction mixture was evaporated to dryness and 2-oxo-3-carboxy-3H-azepin was isolated by preparative column chromatography on silica gel with a mixture of acetone/ethanol (1:1, v/v) with 50% yield as pale yellow crystals. 1H NMR (400 MHz, CDCl3) δ 8.35 (s, 1H), 6.31 – 6.17 (m, 2H), 5.93 (ddd, J = 14.1, 9.2, 5.5 Hz, 2H), 3.53 (dd, J = 5.8, 1.6 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 168.9, 164.6, 126.8, 125.5, 121.3, 114.8, 52.9, 52.8; IR (suspension in nujol oil, cm-1 ): 3198 cм-1 (νs NH); 1714 cм-1 (νs С=O carboxyl group); 1658 cм-1 (νs C=O amide)
