[F:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=O)=[CH:4][CH:3]=1.CN(C=O)C.[C:16]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])(=[O:19])[NH:17][NH2:18].C(Cl)CCl>C(OCC)C.C1COCC1>[C:21]([O:20][C:16]([NH:17][NH:18][C:6](=[O:8])[C:5]1[CH:4]=[CH:3][C:2]([F:1])=[CH:10][CH:9]=1)=[O:19])([CH3:24])([CH3:23])[CH3:22]To a solution of 4-fluorobenzoic acid (35.7 mmol) in 72 mL of a mixture of DMF and THF (1:1), is added tert-butyl carbazate (37.5 mmol), EDC (39.3 mmol) and N,N-dimethylaminopyridine (0.54 mmol). After 10 minutes the mixture becomes homogeneous and stirring is continued for 3 hours until the reaction is complete by TLC and LC/MS. The reaction mixture is poured into ice. Upon addition of diethylether the organic layer is separated. The organic layer is washed with sodium bisulfite, saturated sodium bicarbonate and saturated sodium chloride solution, dried over magnesium sulfate and concentrated to yield N′-(4-fluoro-benzoyl)-hydrazinecarboxylic acid tert-butyl ester: MS: (ES+) 255 (M+1)+.
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