Dicyclohexylamine → (2-Fluoro-5-methyl-phenyl)-acetic acid tert-butyl ester

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In analogy to the procedure described in M. Jørgensen et al., J. Am. Chem. Soc. 124 (2002), 12557-12565, in a first flask, dicyclohexylamine (3.06 g, 16.9 mmol) was dissolved in toluene and cooled in an ice bath. n-Butyllithium (6.14 ml, 2.5 M solution in hexane) was added. After 5 min, tert-butyl acetate (1.78 g, 15.3 mmol) was added slowly. A second flask was charged with tri-(tert-butyl)phosphonium tetrafluoroborate (83 mg, 0.30 mmol) and tris(dibenzylideneacetone)dipalladium(0) (146 mg, 0.153 mmol) and thoroughly flushed with argon. Toluene (100 ml) was added, followed by 3-bromo-4-fluoro-toluene (2.90 g, 15.3 mmol) and by the contents of the first flask. After stirring overnight, the formed suspension was filtered over a small plug of silica gel which was washed repeatedly with diethyl ether. The filtrates were evaporated in vacuo and the residue was purified by silica gel chromatography (HEP/EA gradient) to give 2.81 g of (2-fluoro-5-methyl-phenyl)-acetic acid tert-butyl ester.

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