General procedure for the synthesis of 2,1,3-benzothiadiazole-5-carbaldehyde from 2,1,3-benzothiadiazole-5-methanol: A mixed solution of benzo[1,2,5]thiadiazol-5-ylmethanol (115 mg, 0.69 mmol) and manganese dioxide (241 mg, 2.8 mmol) in chloroform (10 mL) was stirred and reacted overnight at room temperature. Upon completion of the reaction, the mixture was filtered through a diatomaceous earth pad and the filtrate was concentrated under reduced pressure to afford pure 2,1,3-benzothiadiazole-5-carbaldehyde (111 mg, 98% yield). The structure of the product was confirmed by 1H NMR (300 MHz, CDCl3): δ 10.19 (s, 1H), 8.49 (s, 1H), 8.09 (s, 2H).
