Reaction #9854

Reaction equation

hexane

2-bromoethanol

3,5-dibromo-4-nitropyrazole

NaH

→

2-(3,5-dibromo-4-nitropyrazol-1-yl)ethanol

Solvents

DMF

DMF

DMF

Conditions

Workup

1. 1
   Otherthe DMF was evaporated off under reduced pressure
2. 2
   workup.ADDITIONA mixture of DCM/water (100 ml, 1/1)
3. 3
   workup.ADDITIONis added to the residue
4. 4
   Washthe organic phase is washed with water (50 ml)
5. 5
   DryingThe organic phase was dried over Na2SO4
6. 6
   Otherthe solvent was evaporated off under reduced pressure
7. 7
   OtherThe crude brown solid obtained
8. 8
   Otherwas subsequently purified by column chromatography (5%/95% EtOAc/hexane)
9. 9
   OtherThe yellow solid product (3.4 g) was recrystallized from a mixture of toluene/hexane (20 ml, 55%/45%)

Procedure

A solution of 3,5-dibromo-4-nitropyrazole (2) (11.0 g, 41 mmol) in DMF (52 ml) was added dropwise over 20 min to a stirred solution of NaH (1.76 g, 46 mmol; 60% dispersion in oil, prewashed with hexane under an inert atmosphere) in DMF (88 ml). After stirring for 10 minutes, a solution of 2-bromoethanol (6.4 g, 49 mmol) in DMF (14 ml) was added dropwise over 10 minutes. The reaction mixture was heated to 80° C. for 2 hours and then the DMF was evaporated off under reduced pressure. A mixture of DCM/water (100 ml, 1/1) is added to the residue and the organic phase is washed with water (50 ml). The organic phase was dried over Na2SO4 and the solvent was evaporated off under reduced pressure. The crude brown solid obtained was subsequently purified by column chromatography (5%/95% EtOAc/hexane). The yellow solid product (3.4 g) was recrystallized from a mixture of toluene/hexane (20 ml, 55%/45%) to give the 2-(3,5-dibromo-4-nitropyrazol-1-yl)ethanol (3) in the form of a white solid (2.8 g, 22%).

Source