2-[(2-Aminothiazol-4-yl)-(benzothiazol-2-ylsulfenylcarbonyl)-methyleneamino-oxy]-2-methylpropionic acid t-butyl ester,a key intermediate for ceftazidime,was prepared from 2-[(2-aminothiazol-4-yl)-carboxymethyleneamino-oxy]-2-methylpropionic acid t-butyl ester(2) and dibenzothiazolyl disulfide(3) by esterification in toluene in presence of Ph3P and Et3N with 85.4% yield.The molar ratio of 2,3,Ph3P and Et3N was 1∶1.16∶1.16∶0.4.

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