General procedure for the synthesis of 3-fluoro-4-iodocyanopyridine from 2-cyano-3-fluoropyridine:
Preparation of 3-fluoro-4-iodopyridine-2-carbonitrile (86A):
1. In a dry reaction flask, dissolve diisopropylamine (2.80 mL, 19.66 mmol) in tetrahydrofuran (THF, 201 mL) and cool to -78 °C.
2. n-Butyllithium (7.86 mL, 19.66 mmol) was added slowly and dropwise to the above solution.
3. Transfer the reaction mixture from a dry ice/acetone bath to an ice water bath and stir at 0 °C for 25 min, followed by cooling again to -78 °C.
4. In another dry reaction flask, 3-fluoropyridine-2-carbonitrile (1.5 g, 12.29 mmol) was dissolved in THF (50 mL) and cooled to -78 °C. The reaction mixture was then stirred for 25 min at 0 °C.
5. LDA (130 mL, 1.0 eq.) was added to this solution and the solution turned dark red.
6. After 35 minutes, iodine (3.43 g, 13.51 mmol) was added rapidly.
7. The reaction mixture was stirred at -78 °C for 45 min, followed by quenching the reaction with deionized water (H2O).
8. The organic and aqueous layers were separated and the aqueous phase was extracted with dichloromethane (CH2Cl2, 2 x 50 mL).
9. The organic phases were combined, dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated to give a brown residue.
10. The crude product was dissolved in a minimal amount of dichloromethane and prepared for column chromatographic separation.
11. Purification by silica gel column chromatography using an ISCO automated purification system (80 g silica gel column, flow rate 60 mL/min, eluent 0-20% ethyl acetate in hexane solution, run time 23 min, retention time 18 min) afforded 3-fluoro-4-iodo-pyridine-2-carbonitrile (1.7 g, 6.79 mmol, yield 55.2%) as a brown solid.
