1 H NMR ( CDCl 3 , 300 MHz ) δ 8 . 58 ( s , 1 H ) , 7 . 56 - 7 . 53 ( d , 1 H , J = 9 . 4 Hz ) , 6 . 62 - 6 . 59 ( d , 1 H , J = 9 . 4 Hz ) , 5 . 83 ( s , 1 H ) , 2 . 66 ( s , 3 H ) , 1 . 65 ( d , 6 H ) .