1H NMR (400 MHz, CDCl3): δ 7.65 (d, J = 7.7 Hz, 2H), 7.45 (t, J = 7.4 Hz, 1H), 7.35 (t, J = 7.6 Hz, 2H), 5.83 (s, 1H), 5.54 (s, 1H), 1.99 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 198.3, 143.7, 137.7, 132.0, 129.4, 128.1, 127.1, 18.6.