1 H - NMR ( CDCl 3 ) δ 8 . 67 ( pseudo t , 1 H , J = 1 . 4 Hz ) , 8 . 23 ( s , 1 H ) , 5 . 88 ( s , 1 H ) , 5 . 23 ( m , 2 H , ) , 3 . 69 ( dd , 1 H , J = 4 . 0 , 13 . 2 Hz ) , 3 . 18 ( d , 1 H , J = 12 . 8 Hz ) , 1 . 52 ( s , 3 H ) , 1 . 29 ( s , 3 H ) ;