1 H NMR ( 300 MHz , DMSO - d 6 ) δ 9 . 07 ( s , 1 H ) , 8 . 92 ( s , 1 H ) , 7 . 93 ( d , 2 H , J = 8 . 7 Hz ) , 7 . 63 ( d , 2 H , J = 8 . 7 Hz ) , 7 . 49 ( d , 2 H , J = 9 . 0 Hz ) , 7 . 33 ( d , 2 H , J = 8 . 9 Hz ) , 3 . 87 ( s , 2 H ) , 2 . 28 ( s , 6 H ) ; MS ( m / z ) : 371 ( M +).