[Synthesis]
General procedure for the synthesis of 4-iodo-2-methoxypyridine-3-carboxaldehyde (DeTMS-PM): tert-butyl lithium (1.5 M in n-pentane, 6.9 mL, 9.16 x 1.1 mmol) was added slowly and dropwise to a solution of 2-methoxypyridine (1.00 g, 9.16 mmol) in dry THF (7.5 mL) at -75 °C to -60 °C and stirred at the same temperature for 1 hour. Subsequently, a solution of anhydrous THF (10 mL) of FEO (1.44 g, 9.16 x 1.2 mmol) was added dropwise at the same temperature and stirring was continued for 30 min. The temperature of the reaction system was raised to about -23 °C, ethylene glycol dimethyl ether (DME, organic synthesis grade, 7.5 mL) was added, followed by dropwise addition of n-butyllithium (1.6 M in hexane, 9.9 mL, 9.16 x 1.7 mmol), and the reaction was maintained between -15 °C and -25 °C and stirred for 2 hours at about -23 °C. The mixture was cooled to about -70 °C, a solution of iodine (4.42 g, 9.16 x 1.9 mmol) in DME (10 mL) was added quickly and stirred at about -70 °C for 30 minutes. After warming to room temperature, 10% Na2SO3 solution (in appropriate amount until the color of iodine disappeared) was added and stirred for 10 min, followed by extraction with water, brine and ethyl acetate (50 mL). The organic layer was separated, dried with Na2SO4, filtered and concentrated to dryness. The residue (brown solid) was dissolved in chloroform and purified by medium-pressure silica gel column chromatography (n-hexane: ethyl acetate = 1000:1 → 100:1). The desired grades were collected and concentrated to dryness to give DeTMS-PM (1.31 g, 4.98 mmol, 54%) as a yellow solid. The product was confirmed by 1H-NMR (400 MHz, CDCl3): δ 4.05 (3H, s, MeO), 7.54 (1H, d, J = 5.4 Hz, Aromatic-H), 7.85 (1H, d, J = 5.4 Hz, Aromatic-H), 10.21 (1H, s, CHO).IR (KBr) showed characteristic absorption peaks (cm-1): 2943, 1697 (CHO), 1543, 1458, 1362, 1015.EI-MS (m/z): 263 [M]+ (100%). |