1H NMR (400 MHz, CDCl3) δ 8.58 (s, 1H), 6.87 (m, 3H), 6.03 (s, 2H); 13C NMR (101 MHz, CDCl3) δ 159.7 (s), 148.8 (s), 148.1 (s), 123.0 (s), 117.6 (s), 116.6 (s), 109.3 (s), 108.7 (s), 101.7 (s). HRMS (EI): calculated for C10H6N2O5: 234.0277; found: 234.0274.