1 H - NMR : ( 300 MHz , DMSO - d 6 ) δ 9 . 87 ( s , 1 H ) , 8 . 22 ( s , 1 H ) , 7 . 41 ( dd , 1 H , J = 3 Hz , 3 Hz ) , 7 . 29 ( m , 2 H , J = 3 Hz , 3 Hz , 9 Hz ) , 5 . 94 ( s , 1 H ) , 3 . 44 ( d , 7 H , J = 6 Hz ) , 2 . 74 ( t , 3 H , J = 6 Hz , 3 Hz ) , 2 . 40 ( s , 3 H ) , 2 . 24 ( s , 3 H ) ;