Hydrogen Bromide → 3-Iodo-7-trifluoromethyl-5-(4-trifluoromethyl-phenyl)-pyrazolo[1,5-a]pyridine

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Reaction Conditions

Reaction Steps

A mixture of 7-trifluoromethyl-5-(4-trifluoromethyl-phenyl)-pyrazolo[1,5-a]pyridine-3-carboxylic acid (example C.22 step 8) (650 mg, 1.74 mmol) in acetic acid (20 mL) containing HI (57%, 200 uL) was refluxed for 2 days, but only 30% conversion. Added HBr (48%, 2 mL, 18 mmol) and continued refluxing for 2 h. Cooled to 23° C., added NaOAc (2.5 g, 30 mmol) and ICl (2M in HOAc, 6.1 mL, 12.2 mmol) and the mixture was stirred at 23° C. for 1 h. Added sat. Na2SO3-sol. to destroy excess ICl, diluted with water, filtered precipitate off, washed with water, dissolved in TBME, washed with sat. NaHCO3-sol. and brine, dried over Na2SO4. Removal of the solvent in vacuum left the title compound as a light yellow solid (740 mg, 93%; LC-MS shows mixture of bromide and iodide). MS (for iodide) (ISP) 456.2 [(M+H)+].

Provenance & Evidence