2,2,6,6-Tetramethylpiperidine → 2-Bromo-4-chloro-3-fluoropyridine

Temperature

0 °C

To a solution of 2,2,6,6-tetramethylpiperidine (25 g, 190 mmol) in hexanes (100 mL) cooled over dry ice acetone bath for 5 minutes was added 1.6M n-butyl lithium in hexanes (121 mL, 194 mmol) over 5 minutes. After the addition was complete, the reaction mixture was placed in an ice bath and the mixture was allowed to stir at 0° C. for 20 minutes as a white solid formed. The suspension was re-cooled over dry ice/acetone bath for 5 minutes and then treated with a solution of 4-chloro-3-fluoropyridine (25 g, 190 mmol) in hexanes (50 mL) over 5 minutes and this mixture was stirred over dry ice/acetone bath for additional 10 minutes. After this time, this mixture was treated with bromine (30.4 mL, 190 mmol) and stirred over dry ice/acetone bath for 15 minutes. After this time, the reaction mixture was stirred for 30 minutes at 0° C. and then allowed to warm to room temperature. The reaction mixture was re-cooled over wet ice bath and quenched with water (200 mL) and extracted with ether (3×300 mL). The combined organic extracts were washed with water, dried (MgSO4), and the solvent removed in vacuo. The residue was purified by chromatography using 330 g silica gel cartridge and eluting with a gradient of 20-100% CH2Cl2 in hexanes to provide the title compound. 1H NMR (CDCl3) δ=8.13 (d, 1H, J=5.1 Hz) and 7.35 (dd, 1H, J=5 Hz) ppm.

1. additionAfter the addition
2. customthe reaction mixture was placed in an ice bath
3. customformed
4. temperatureThe suspension was re-cooled over dry ice/acetone bath for 5 minutes
5. stirringthis mixture was stirred over dry ice/acetone bath for additional 10 minutes
6. stirringstirred over dry ice/acetone bath for 15 minutes
7. stirringAfter this time, the reaction mixture was stirred for 30 minutes at 0° C.
8. temperatureto warm to room temperature
9. temperatureThe reaction mixture was re-cooled over wet ice bath
10. customquenched with water (200 mL)
11. extractionextracted with ether (3×300 mL)
12. washThe combined organic extracts were washed with water
13. dry with materialdried (MgSO4)
14. customthe solvent removed in vacuo
15. customThe residue was purified by chromatography
16. washeluting with a gradient of 20-100% CH2Cl2 in hexanes

ORD record

ord-cbbc654c993d46cd80c2edcdbdbbc80b

Source dataset

uspto-grants-2013_03

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US08404856B2