1 H NMR ( 300 MHz , CDCl 3 ) δ 3 . 84 ( s , 3 H ) , 3 . 99 ( dt , 2 H , J = 5 . 7 , 1 . 8 Hz ) , 4 . 19 ( s , 3 H ) , 4 . 23 ( dd , 2 H , J = 6 . 9 , 2 . 4 Hz ) , 5 . 16 ( dd , 1 H , J = 10 . 2 , 1 . 2 Hz ) , 5 . 26 ( dd , 1 H , J = 15 . 9 , 1 . 2 Hz ) , 5 . 88 - 5 . 98 ( m , 2 H ) , 6 . 71 ( d , 1 H , J = 2 . 4 Hz ) , 6 . 81 ( d , 1 H , J = 12 . 0 Hz ) , 7 . 03 ( s , 1 H ) , 7 . 59 ( d , 1 H , J = 2 . 4 Hz )