1 H NMR ( 300 MHz , CDCl 3 ) δ 9 . 92 ( s , 1 H ) , 7 . 48 - 7 . 43 ( m , 2 H ) , 7 . 30 ( d , J = 6 . 8 Hz , 1 H ) , 6 . 70 ( td , J = 99 . 6 , 0 . 9 Hz , 1 H ) , 4 . 20 - 4 . 14 ( m , 2 H ) , 1 . 50 - 1 . 45 ( m , 3 H ) .