Synthesis
General procedure for the synthesis of 2,5-dichlorobenzoxazole from 5-chloro-2-mercaptobenzoxazole: Thionyl chloride (885 g, 7.5 mol) and N,N-dimethylformamide (270 ml) were added drop-wise to a solution of 5-chloro-2-mercaptobenzoxazole (540 g, 2.903 mol) in dichloromethane (5 L) at 5-10°C. The reaction mixture was stirred until a clarified solution was formed, followed by continued stirring for 4 hours at room temperature. Upon completion of the reaction, the reaction solution was slowly poured into 4 L of ice water and neutralized with sodium bicarbonate to pH neutral within 1 hour. The aqueous phase was extracted with dichloromethane (2.5 L x 2) and the combined organic layers were washed with saturated brine and dried over anhydrous sodium sulfate. The organic phase was concentrated under reduced pressure to give the crude product. The crude product was washed with n-hexane (2L×2) at -20°C, filtered and dried to give a yellow liquid 2,5-dichlorobenzoxazole (496.8 g, 91.0% yield).
References
[1] Patent: CN106478537, 2017, A. Location in patent: Paragraph 0027; 0028; 0039; 0040; 0050; 0051; 0065; 0066
[2] Patent: US2016/168138, 2016, A1. Location in patent: Paragraph 0144-0145
[3] Bioorganic and Medicinal Chemistry Letters, 2013, vol. 23, # 3, p. 907 - 911
[4] Advanced Synthesis and Catalysis, 2017, vol. 359, # 11, p. 1837 - 1843
[5] Journal of Medicinal Chemistry, 1988, vol. 31, # 9, p. 1719 - 1728
