Triethylsilane → ethyl 2-ethyl-5-(tetrahydro-2H-pyran-4-yl)thiophene-3-carboxylate

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To a solution of ethyl 5-bromo-2-ethylthiophene-3-carboxylate (5.00 g) synthesized in Example 69 (4) in tetrahydrofuran (50 mL) was added dropwise 1.0M isopropylmagnesium bromide-tetrahydrofuran solution (22.8 mL) at −45° C., and the mixture was stirred for 1 hr under an argon atmosphere. Tetrahydro-4H-pyran-4-one (5.26 mL) was added dropwise, and the mixture was stirred at −45° C. for 1 hr, and then at room temperature for 2 hr. Saturated aqueous ammonium chloride solution was added to quench the reaction, tetrahydrofuran was evaporated using evaporator, and the mixture was extracted with ethyl acetate. The extract was washed with saturated brine, dried over magnesium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate:hexane=2:3, volume ratio) to give a colorless oil. To a solution of the obtained oil in trifluoroacetic acid (25 mL) was added triethylsilane (2.86 mL), and the mixture was stirred at room temperature for 1.5 hr, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate:hexane=3:17, volume ratio) to give the title compound (1.35 g, 26%) as a colorless oil.

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