C=O.[CH3:3][O:4][C:5](=[O:14])[C:6]1[CH:11]=[CH:10][C:9]([NH2:12])=[CH:8][C:7]=1[F:13].[C:15](O)(=O)C.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+]>ClCCCl>[CH3:3][O:4][C:5](=[O:14])[C:6]1[CH:11]=[CH:10][C:9]([NH:12][CH3:15])=[CH:8][C:7]=1[F:13]
Add formaldehyde (0.15 g) to a mixture of 2-fluoro-4-amino benzoic acid methyl ester (0.62 g), acetic acid (2.1 mL) and 1,2 dichloroethane (20 mL). Stir at room temperature overnight. Add sodium triacetoxyborohydride (1.15 g) and stir at room temperature for 2 hours. Quench by pouring the reaction mixture into a mixture of saturated aqueous sodium bicarbonate and ethyl acetate. Separate the layers, wash the organic phase with water, dry the remaining organic phase over sodium sulfate and then concentrate under reduced pressure. The residue is purified by chromatography eluting with ethyl acetate:hexane (1:4) to provide 2-fluoro-4-methylamino benzoic acid methyl ester (0.10 g, 15%) as an oil.
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