[F:1][C:2]1[CH:19]=[CH:18][C:5]([CH2:6][N:7]([CH:16]=[O:17])[NH:8]C(OC(C)(C)C)=O)=[CH:4][CH:3]=1.C(O)(C(F)(F)F)=O.C([O-])(O)=O.[Na+]>C(Cl)Cl>[F:1][C:2]1[CH:19]=[CH:18][C:5]([CH2:6][N:7]([CH:16]=[O:17])[NH2:8])=[CH:4][CH:3]=1To a solution of tert-butyl 2-(4-fluorobenzyl)-2-formylhydrazinecarboxylate (0.11 g, 0.410 mmol, 1.0 equiv) in CH2Cl2 (1.02 mL) was added TFA (1.02 mL). Gas evolution was observed. After stirring 30 min, the reaction was poured into a saturated aqueous solution of NaHCO3 and extracted with CH2Cl2 (×3). The combined CH2Cl2 extracts were dried (Na2SO4) and then concentrated in vacuo to provide the title compound (0.056 g, 81% yield) as a viscous yellow oil. 1H NMR (400 MHz, CDCl3) δ ppm (first tautomer) 8.24 (s, 1H), 7.18-7.31 (m, 2H), 7.00-7.14 (m, 2H), 4.47 (s, 2H), 4.11 (s, 2H), (second tautomer) 8.37 (s, 1H), 7.18-7.31 (m, 2H), 7.00-7.13 (m, 2H), 4.62 (s, 2H), 3.63 (s, 2H); LCMS (ES+, (M+H)+) m/z 169.27.
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