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235 mg (0.783 mmol) of 2-methyl-3-(methylthio)-4-(pentafluoroethyl)benzoic acid were introduced into 20 ml of dry dichloromethane and admixed in succession with 129 mg (1.02 mmol) of oxalyl chloride and also with two drops of N,N-dimethyl-formamide. After the end of evolution of gas, the mixture was heated under reflux for another 10 minutes. Then, the contents were cooled and concentrated on a rotary evaporator. The residue was taken up in 20 ml of dry dichloromethane and admixed with 119 mg (0.861 mmol) of bicyclo[3.2.1]octane-2,4-dione and a catalytic amount of DMAP. Then 158 mg (1.57 mmol) of triethylamine were added dropwise. The mixture was stirred at RT for 16 hours. For working up, 3 ml of 1N hydrochloric acid were added. Following phase separation, the organic phase was freed from the solvent and the residue, finally, was purified by chromatography. This gave 280 mg of product with a purity of 90% by weight.

1. temperatureAfter the end of evolution of gas, the mixture was heated
2. temperatureunder reflux for another 10 minutes
3. temperatureThen, the contents were cooled
4. concentrationconcentrated on a rotary evaporator
5. customFollowing phase separation
6. customthe residue, finally, was purified by chromatography