Toluene → Tert-butyl (2-fluoro-3-methoxyphenyl)carbamate

Participants

Reaction Steps

A solution of 2-fluoro-3-methoxybenzoic acid (5.00 g, 29.39 mmol) and diisopropylethylamine (4.56 g, 35.27 mmol) in a mixture of anhydrous toluene (25 mL) and anhydrous tert-butanol (25 mL) was stirred over activated 4 Å molecular sieves (4 g) for 1 h. Diphenyl phosphoryl azide (9.71 g, 35.27 mmol) was added and the mixture was heated at reflux for 15 h. The reaction mixture was cooled and filtered. To the filtrate was added ethyl acetate (200 mL) and the solution was washed with water (2×100 mL) and brine (100 mL). The organic phase was separated and dried over MgSO4. Filtration followed by concentration under reduced pressure gave crude tert-butyl 2-fluoro-3-methoxyphenylcarbamate. The crude product was dissolved in a solution of 6M HCl in ethyl acetate (20 mL, 0.12 mol) and the mixture stirred at rt for 2 h. The resulting precipitate was filtered and dried. The solid was taken up in a saturated aqueous solution of sodium hydrogen carbonate (50 mL) and the mixture extracted with dichloromethane (2×100 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated under reduced pressure to afford 2-fluoro-3-methoxyaniline (3.00 g, 72%) as brown oil, which was taken on without further purification. 1H NMR (400 MHz, DMSO-d6) δ 6.80-7.02 (m, 3H), 3.82 (s, 3H); LC-MS (ESI) m/z 142 (M+H)+.

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