1 H NMR ( 300 MHz , CDCl 3 ) δ 2 . 08 ( s , 3 H ) , 4 . 24 ( s , 3 H ) , 4 . 50 ( dt , 2 H , J = 5 . 7 , 1 . 2 Hz ) , 4 . 81 ( dd , 2 H , J = 6 . 6 , 1 . 8 Hz ) , 5 . 21 ( dd , 1 H , J = 10 . 5 , 1 . 8 Hz ) , 5 . 35 ( dd , 1 H , J = 17 . 1 , 1 . 8 Hz ) , 5 . 86 ( dt , 1 H , J = 11 . 7 , 6 . 6 Hz ) , 6 . 09 ( ddt , 1 H , J = 17 . 1 , 10 . 5 , 5 . 7 Hz ) , 6 . 72 ( d , 1 H , J = 2 . 1 Hz ) , 6 . 86 ( d , 1 H , J = 11 . 7 Hz ) , 7 . 02 ( s , 1 H ) , 7 . 59 ( d , 1 H , J = 2 . 1 Hz )