The general procedure for the synthesis of 3-methyl-2-oxo-2,3-dihydro-1,3-benzazole-6-sulfonyl chloride from 3-methyl-2-benzoxazolidinone was as follows: 3-methyl-2-benzoxazolidinone (0.600 g, 4.02 mmol) was slowly added to chlorosulfonic acid (2.343 g, 20.1 mmol) in batches at 0 °C. After the addition was completed, the reaction system was warmed up to 60 °C and the reaction was continuously stirred for 2 hours. Upon completion of the reaction, the mixture was cooled to room temperature and slowly poured into crushed ice, at which point a precipitate was generated. The precipitate was collected by filtration. The resulting solid was dissolved in ethyl acetate (EtOAc), the organic layer was washed sequentially with water and saturated brine, dried over anhydrous magnesium sulfate (MgSO4), and concentrated under reduced pressure to give a light brown solid product, 3-methyl-2-oxo-2,3-dihydro-1,3-benzazole-6-sulfonyl chloride (0.903 g, 91% yield). The product was characterized by 1H NMR (300 MHz, CDCl3): δ 7.99 (dd, J=8.4,1.8Hz, 1H), 7.89 (d, J=1.6Hz, 1H), 7.17 (d, J=8.4Hz, 1H), 3.52 (s, 3H), which is in accordance with the data reported in literature.
