Synthesis
Example 1A: To a 1 L four-necked round-bottomed flask equipped with a mechanical stirrer, a thermometer and a reflux condenser tube were sequentially added 75.6 g (0.5 mol) of 1,2-benzisothiazol-3-one, 54.8 g (0.75 mol) of N,N-dimethylformamide (DMF) and 100.0 g of chlorobenzene as a solvent. Stirring was turned on and the temperature of the reaction system was maintained between 70 °C and 80 °C, followed by the slow dropwise addition of 71.4 g (0.6 mol) of thionyl chloride (SOCl2) over a period of 1 hour. After the dropwise addition was completed, the reaction mixture was kept at the same temperature and the reaction was continued with stirring for 8 hours. Upon completion of the reaction, the liquid reaction mixture was concentrated under reduced pressure to remove the solvent and unreacted thionyl chloride. The resulting crude product was subjected to decompression distillation at 128 °C under reduced pressure at 0.93 kPa to yield 75.1 g (0.45 mol) of the target product 3-chloro-1,2-benzisothiazole in 90% yield as 1,2-benzisothiazol-3-one.
References
[1] Patent: US5883258, 1999, A
[2] Patent: US2013/5983, 2013, A1. Location in patent: Page/Page column 2-3
[3] Patent: US5883258, 1999, A
[4] Tetrahedron Letters, 2011, vol. 52, # 50, p. 6775 - 6778
[5] Journal of Medicinal Chemistry, 1986, vol. 29, # 3, p. 359 - 369
