1 H - NMR ( 250 MHz , CDCl 3 ) δ 7 . 78 ( d , 2 H , J = 8 . 37 Hz ) , 7 . 45 - 7 . 33 ( m , 7 H ) , 4 . 96 ( d , 1 H , J = 8 . 42 Hz ) , 4 . 08 ( dd , 2 H , J 1 = 10 . 37 Hz , J 2 = 3 . 27 Hz ) , 2 . 53 ( d , 1 H , J = 3 . 17 Hz ) , 2 . 45 ( s , 3 H )