General procedure for the synthesis of 2-hydroxy-5-iodo-3-(trifluoromethyl)pyridine from 2-hydroxy-3-trifluoromethylpyridine:
1. 3-Trifluoromethyl-2-pyridinol (25 g, 153.3 mmol) was dissolved in a mixed solvent of anhydrous acetonitrile (150 mL) and N,N-dimethylformamide (150 mL).
2. N-iodosuccinimide (34.5 g, 153 mmol) was added to the above solution.
3. The reaction mixture was stirred at 80 °C for 2 hours and subsequently cooled to room temperature.
4. 1 M aqueous sodium bicarbonate (150 mL) was added to the cooled reaction mixture and stirred for 5 minutes.
5. The mixed solvents were evaporated to dryness, an appropriate amount of water was added and the aqueous phase was extracted twice with dichloromethane.
6. The organic phases were combined and evaporated, and the resulting crude product was recrystallized in water to give 36.2 g (81% yield) of a white powdery target product, 2-hydroxy-5-iodo-3-(trifluoromethyl)pyridine.
Product characterization data:
1H NMR (500 MHz, CDCl3) δ 7.85 (d, J = 2.3 Hz, 1H), 7.98 (d, J = 2.3 Hz, 1H), 13.41 (br s, 1H).
13C NMR (250 MHz, CDCl3) δ 63.0, 121.4 (q, JC-F = 272.3 Hz), 122.2 (q, JC-F = 31.6 Hz), 144.4, 148.1 (q, JC-F = 5.0 Hz), 160.1.
