Chlorotrimethylsilane → 1-Bromo-2,4,5-trifluoro-3-(trimethylsilyl)benzene

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This preparation route is very expensive. The first and the second synthesis step each involve reaction with butyllithium and diisopropylamine in tetrahydrofuran at −78° C., and the third synthesis step involves reaction with butyllithium in ether, likewise at −78° C. In the first step, 1-bromo-2,4,5-trifluorobenzene is reacted first with lithium diisopropylamide and then with trimethylsilyl chloride, the resulting 1-bromo-2,4,5-trifluoro-3-(trimethylsilyl)benzene (88% yield) is once more reacted with lithium diisopropylamide and subsequently with methyl trifluoromethanesulfonate, the resulting 1-bromo-2,4,5-trifluoro-6-methyl-3-(trimethylsilyl)benzene (75% yield) is reacted with butyllithium and subsequently with CO2 in the form of dry ice, and the resulting 2,4,5-trifluoro-6-methyl-3-(trimethylsilyl)- benzoic acid (62% yield) is reacted with cesium fluoride in acetonitrile to give 6-methyl-2,4,5-trifluorobenzoic acid (89% yield).

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