Reaction #76767

Reaction equation

sodium hydrogencarbonate

ethyl 2-chloro-4-fluoro-5-hydrazinobenzoate hydrochloride

sodium acetate

1,1-dibromo-3,3,3-trifluoroacetone

→

ethyl 2-chloro-4-fluoro-5-hydrazinobenzoate

Solvents

water

diethyl ether

water

Conditions

Workup

1. 1
   workup.ADDITIONwas added
2. 2
   Temperaturewhile cooling
3. 3
   Washby washing with saturated sodium chloride solution, which

Procedure

To a mixed aqueous solution of 5.3 g (53.5 mmol) of sodium acetate and about 100 ml of water was added under ice cooling 6.6 g (24.3 mmol) of 1,1-dibromo-3,3,3-trifluoroacetone, and the reaction was allowed to proceed at 70° C. for 20 minutes. Then, the reaction mixture was cooled to room temperature. Separately, 5.8 g (21.5 mmol) of ethyl 2-chloro-4-fluoro-5-hydrazinobenzoate hydrochloride was dissolved in 30 ml of water, to which 100 ml of diethyl ether was added, and while cooling, the mixture was neutralized by the addition of saturated sodium hydrogencarbonate solution, followed by washing with saturated sodium chloride solution, which afforded a solution of ethyl 2-chloro-4-fluoro-5-hydrazinobenzoate in diethyl ether. This solution was added to the above reaction mixture, followed by vigorous stirring at room temperature for 2 hours. The ether layer was separated, washed once with 10 ml of saturated sodium chloride solution, and dried with magnesium sulfate. The diethyl ether was distilled out, and a small amount of hexane was added to give 4.3 g (12.6 mmol) of ethyl 2-chloro-4-fluoro-5-(2-oxo-3,3,3-trifluoropentylidenehydrazino)benzoate. This product was dissolved in 50 ml of THF, to which 5.0 g (14.4 mmol) of carbethoxymethylenetriphenylphosphorane was added, and the mixture was heated under reflux for 2 hours. The THF was distilled out under reduced pressure, and the residue was subjected to silica gel column chromatography, which afforded 3.6 g (9.7 mmol) of compound 1-1279.

Source