General procedure for the synthesis of 3-iodopyridine-2-carboxylic acid from 2-pyridinecarboxylic acid: 2,2,6,6-tetramethylpiperidine (8.48 g, 60 mmol) was dissolved in tetrahydrofuran (100 mL), cooled to -78 °C, and N-butyllithium (2.5 mol/L, 16 mL, 40 mmol) was added slowly dropwise. After the dropwise addition, it was slowly warmed up to room temperature and kept for 30 minutes. Cooled again to -78 °C, the solution was added dropwise to a tetrahydrofuran suspension of pyridine-2-carboxylic acid (2.46 g, 20 mmol). After completion of the dropwise addition, the reaction mixture was allowed to react at room temperature for 30 minutes. Subsequently cooled to -30°C, a tetrahydrofuran solution of iodine (15.23 g, 60 mmol) was added dropwise to the reaction flask. The mixture was stirred at room temperature for 1 h. Water was added and left overnight to precipitate the solid. Filtration gave 3-iodopyridine-2-carboxylic acid (3.3 g, 66% yield).
