1H NMR (400 MHz, CDCl3) δ 9.21 (s, 1H), 8.92 (s, 2H), 7.86 (d, J = 7.9 Hz, 2H), 7.31 (d, J = 7.8 Hz, 2H). 13C NMR (101 MHz, CDCl3) δ 157.77, 154.63, 138.59, 133.70, 133.39, 128.61, 95.23.