1 H NMR ( 300 MHz , CDCl 3 ) δ 4 . 06 - 4 . 38 ( m , 2 H ) , 3 . 48 ( ddd , J = 7 . 2 , 10 . 2 , 21 . 9 Hz , 1 H ) , 3 . 28 ( dd , J = 7 . 2 , 29 . 5 Hz , 1 H ) , 2 . 85 - 3 . 04 ( m , 3 H ) , 2 . 48 - 2 . 65 ( m , 2 H ) , 1 . 64 - 1 . 78 ( m , 2 H ) , 1 . 47 ( s , 18 H ) , 0 . 88 ( s , 3 H ) ;