Reaction #8586

Reaction equation

triethylamine

2-(6-chloro-2-pyridinyl)-1-(4-fluorophenyl)ethanone oxime

trifluoroacetic anhydride

→

7-chloro-2-(4-fluorophenyl)pyrazolo[1.5-α]pyridine

Yield 68.3%

Solvents

1,2-dimethoxyethane

1,2-dimethoxyethane

Conditions

Workup

1. 1
   Otherthe temperature below 10° C
2. 2
   workup.ADDITIONAfter the addition
3. 3
   TemperatureThe solution was then cooled to 4° C.
4. 4
   TemperatureAfter warming to room temperature
5. 5
   Temperaturethe reaction was heated
6. 6
   Temperatureto reflux for 3 hours
7. 7
   ConcentrationThe reaction was concentrated
8. 8
   Otherthe resulting solid was recrystallized from ethyl acetate-hexanes

Procedure

To a solution of 2-(6-chloro-2-pyridinyl)-1-(4-fluorophenyl)ethanone oxime (109.2 g, 414 mmol) in 1,2-dimethoxyethane (500 mL) at 0° C. was added trifluoroacetic anhydride (59 mL, 414 mmol), keeping the temperature below 10° C. After the addition was complete, the reaction was warmed to 15° C. The solution was then cooled to 4° C. and a solution of triethylamine (116 mL, 828 mmol) in 1,2-dimethoxyethane (60 mL) was added over 0.5 hours. After warming to room temperature, the mixture was stirred for 1.5 hours. To this was added iron(II) chloride (0.52 g, 4.1 mmol) and the reaction was heated to reflux for 3 hours. The reaction was concentrated and the resulting solid was recrystallized from ethyl acetate-hexanes to give 7-chloro-2-(4-fluorophenyl)pyrazolo[1.5-α]pyridine (69.7 g. 68%) as off-white needles. 1H NMR (CDCl3): δ 8.03 (m, 2 H), 7.54 (d, 1 H), 7.16 (m, 3 H), 6.93 (d, 1 H), 6.91 (s, 1 H); MS m/z 247 (M+1); mp 156–157° C.

Source