[CH2:1]([O:3][C:4](=[O:19])[CH2:5][NH:6][CH:7]1[CH2:16][CH2:15][C:14]2[C:9](=[CH:10][C:11]([F:18])=[CH:12][C:13]=2[F:17])[CH2:8]1)[CH3:2].[CH:20](OC(=O)C)=[O:21]>C(Cl)Cl>[CH2:1]([O:3][C:4](=[O:19])[CH2:5][N:6]([CH:7]1[CH2:16][CH2:15][C:14]2[C:9](=[CH:10][C:11]([F:18])=[CH:12][C:13]=2[F:17])[CH2:8]1)[CH:20]=[O:21])[CH3:2]A solution of ethyl[(5,7-difluoro-1,2,3,4-tetrahydronaphthalen-2-yl)-amino]acetate (7.15 g, 25.6 mmol) in 20 mL of methylene chloride under argon was cooled to approximately 0° C. Acetic formic anhydride (9.7 mL, 67.3 mmol) was cooled to 0° C. and added over 5 to 10 minutes. The mixture was stirred 0° C. for 2 hours and then allowed to warm to room temperature. The solvent was removed by co-evaporation with toluene (3×50 mL). Crystallization of the residue under high vacuum gave ethyl[(5,7-difluoro-1,2,3,4-tetrahydronaphthalen-2-yl)(formyl)amino]acetate (7.68 g, 25.0 mmol).
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