1H NMR (400 MHz, CDCl3) δ 10.23 (s, 1H), 7.87 (dd, J = 13.6, 6.4 Hz, 2H), 7.75 – 7.65 (m, 2H), 7.53 – 7.40 (m, 2H), 7.22 (s, 1H). 13C NMR (101 MHz, CDCl3) δ 190.65, 141.46, 138.71, 138.13, 136.27, 131.31, 130.72, 129.46, 128.01, 127.67, 127.25, 124.84, 122.43.