To a solution of 760 mg (2.61 mmol) of 6-fluoro-1-triisopropylsilylindole dissolved in 6 ml of anhydrous tetrahydrofuran are added dropwise at −78° C. under argon 2.01 ml of a sec-butyllithium solution (1.3M in cyclohexane, 2.01 mmol). The reaction mixture is stirred for 2 h at −78° C. then 500 μL (3.15 mmol) of diethyl carbonate are added dropwise at −78° C. to the reaction mixture. This mixture is stirred for 5 h with a gentle temperature rise then an ammonium chloride saturated aqueous solution is added. The product is extracted several times with ethyl acetate. The organic phases are combined, dried over magnesium sulfate, and concentrated. The residue is purified by chromatography on silica (cyclohexane/ethyl acetate eluent: 97:3) to yield 445 mg (46%) of 5-carboethoxy-6-fluoro-1-triisopropylsilylindole in the form of a colourless oil.
