Potassium Carbonate → 1-(2-Fluoro-3-methoxy-6-nitrophenyl)propan-2-one

Participants

Reaction Steps

A mixture of 1-(2,3-difluoro-6-nitrophenyl)-propan-2-one (183 g) and potassium carbonate (100 g) in methanol (1 L) was heated at reflux for 3 h. The reaction mixture was then cooled and concentrated in vacuo to remove most of the methanol. The residue was diluted with ethyl acetate (1 L), filtered and washed with water. The separated aqueous layer was neutralized with 2N HCl and extracted with ethyl acetate (2×500 mL). The combined organic layer was washed with brine, dried (Na2SO4) and concentrated in vacuo to give a brown solid. The solid was triturated with diethyl ether and filtered to provide 1-(2-fluoro-3-methoxy-6-nitrophenyl)-propan-2-one (121 g, 71%) as a yellow solid. LC/MS; (M+H)+=228.2. N. A mixture of 1-(2-fluoro-3-methoxy-6-nitrophenyl)-propan-2-one from previous step (454 mg, 21 mmol) and pyridinium chloride (0.9 g, 7.8 mmol) was stirred at 180° C. for 75 min. The reaction was cooled to room temperature, diluted with 1N HCl (3 mL) and ethyl acetate (10 mL) and filtered. The filtrate was washed with brine (2×), dried and concentrated in vacuo to give 1-(2-fluoro-3-hydroxy-6-nitrophenyl)-propan-2-one (410 mg, 96%) as a grey solid, which was used without further purification for the next step. LC/MS; (M+H)+=214. 1HNMR (CDCl3): δ 2.37 (s, 3H), 4.22 (s, 2H), 6.95 (dd, 1H), 7.95 (d, 1H, J=9.35 Hz). O. 1-(2-fluoro-3-hydroxy-6-nitrophenyl)-propan-2-one from previous step (50 g, 0.234 mol) was added to 2 liter round bottom flask. Water (1 L) was added, and the yellow suspension was stirred at RT. Sodium dithionite (225 g, 5.5 eq) was added in one portion and the reaction mixture was stirred and kept <30° C. until HPLC analysis indicated no starting material remained (typically less than 1 hour). Upon completion, the reaction mixture was cooled to 0° C. and the tan solid product was collected by vacuum filtration. The wet product was dried at <50° C. under house vacuum to afford 4-fluoro-2-methyl-1H-indol-5-ol (31.4 g, 81% yield) which was isolated as a tan crystalline powder. The material had an HPLC purity of >99.8. 1H NMR (CDCl3, 400 MHz) δ 7.8 (s, 1H), 6.9-6.7 (m, 2H), 6.2 (s, 1H), 4.7 (s, 1H), 2.4 (s, 3H). 13C NMR (CDCl3, 100 MHz) δ 145.7, 143.4, 137.5, 136.7, 134.4, 120.1, 112.7, 106.8, 95.4, 13.3.

Provenance & Evidence