1H NMR (400 MHz, CDCl3): δ 7.91 (d, J = 7.9 Hz, 2H), 7.55 (t, J = 7.3 Hz, 1H), 7.45–7.41 (m, 4H), 7.37–7.31 (m, 3H), 6.07 (s, 1H), 5.64 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 197.6, 148.3, 137.1, 137.0, 133.1, 130.0, 128.6, 128.4, 127.0, 121.0.