1 H NMR ( 300 MHz , CDCl 3 ) δ : 8 . 51 ( d , J = 7 . 5 Hz , 1 H ) , 8 . 17 ( d , J = 7 . 5 Hz , 1 H ) , 7 . 58 - 7 . 49 ( m , 2 H ) , 6 . 70 ( s , 1 H ) , 4 . 78 - 4 . 76 ( m , 1 H ) , 4 . 22 ( s , 3 H ) , 3 . 97 ( s , 3 H ) , 1 . 58 ( d , J = 6 . 8 Hz , 6 H ) .