General procedure for the synthesis of 2,1,3-benzothiadiazole-5-methanol from 2,1,3-benzothiadiazole-5-carboxylic acid: 2,1,3-benzothiadiazole-5-carboxylic acid (2.00 g, 11.11 mmol) was dissolved in tetrahydrofuran (50 mL) and the solution was cooled to 0 °C. Subsequently, triethylamine (1.80 mL, 12.87 mmol) was slowly added dropwise followed by isobutyl chloroformate (1.62 mL, 12.40 mmol). The reaction mixture was continued to be stirred at 0 °C for 30 min and then filtered into a pre-cooled mixture of sodium borohydride (0.83 g, 21.84 mmol) and ice water (20 mL). The reaction system was kept at 0 °C and stirring was continued for 30 min. Subsequently, the reaction solution was concentrated to one-fourth of the original volume and extracted with dichloromethane (3 x 50 mL). The organic phases were combined and dried with anhydrous sodium sulfate. Finally, the organic phase was concentrated under reduced pressure to afford the target product 2,1,3-benzothiadiazole-5-methanol as a white solid in 81% yield (1.50 g), which could be used for subsequent experiments without further purification.
