Hydrochloric Acid → ethyl N-(2-t-butyl-4-chloro-6-fluorobenzoxazol-7-yl)carbamate

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Under a nitrogen atmosphere, a solution of 3.1 grams (11.0 mmole) of ethyl N-(2-t-butyl-6-fluorobenzoxazol-7-yl)carbamate, 35 mL of acetic acid, and 0.2 mL (2.4 mmole) of concentrated hydrochloric acid was stirred and cooled in an ice bath. During five minutes 2.2 grams (14 mmole) of N,N-dichlorourethane was added via syringe. Upon completion of the addition the reaction mixture was stirred for 4 hours, then analyzed by TLC, which indicated the reaction was complete. The reaction mixture was poured into 100 mL of water, and 15 mL of aqueous saturated sodium bicarbonate solution was carefully added. The reaction mixture was then extracted with two 75 mL portions of diethyl ether, and the combined extracts were concentrated under reduced pressure, yielding a residual oil. The oil was subjected to column chromatography on silica gel with 8:1 hexane:ethyl acetate as the eluant. The product-containing fractions were combined and concentrated under reduced pressure, yielding 2.4 grams of ethyl N-(2-t-butyl-4-chloro-6-fluorobenzoxazol-7-yl)carbamate, m.p. 127°-129° C. The NMR spectrum was consistent with the proposed structure.

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