1H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 8.6 Hz, 2H), 7.18 (dd, J = 17.0, 10.5 Hz, 1H), 6.96 (d, J = 8.6 Hz, 2H), 6.42 (d, J = 17.0 Hz, 1H), 5.87 (d, J = 10.5 Hz, 1H), 3.88 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 189.2, 163.5, 132.1, 131.0, 130.2, 129.3, 113.8, 55.5.