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To a stirred solution of ethyl 5-fluoro-1H-indazole-3-carboxylate (487 mg, 2.3 mmol, J. Heterocycl. Chem. 1964, 1, 239-241) in tetrahydrofuran (4 mL) was added potassium tert-butoxide (289 mg, 2.57 mmol) at 0° C. After stirring at 0° C. for 1 h, 2-iodopropane (438 mg, 2.57 mmol) was added to the mixture. The resulting mixture was stirred at room temperature for 20 h and concentrated under reduced pressure. The mixture was diluted with ethyl acetate (50 mL), washed with water (30 mL) and brine (30 mL). The organic layer was separated, dried over magnesium sulfate, and concentrated under reduced pressure. The resulting residue was chromatographed on a column of silica gel eluting with n-hexane/ethyl acetate (10:1 to 2:1) to give 205 mg (35%) of the title compound as a yellow crystal.

1. stirringThe resulting mixture was stirred at room temperature for 20 h
2. concentrationconcentrated under reduced pressure
3. additionThe mixture was diluted with ethyl acetate (50 mL)
4. washwashed with water (30 mL) and brine (30 mL)
5. customThe organic layer was separated
6. dry with materialdried over magnesium sulfate
7. concentrationconcentrated under reduced pressure
8. customThe resulting residue was chromatographed on a column of silica gel eluting with n-hexane/ethyl acetate (10:1 to 2:1)