2-(Ethylamino)ethanol → Tert-butyl 3-(4-{({4'-[2-(ethylamino)ethoxy]-2',6'-dimethylbiphenyl-3-yl}methyl)[(2-nitrophenyl)sulfonyl]amino}-2-fluorophenyl)propanoate

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To a solution of tert-butyl 3-(2-fluoro-4-{[(4′-hydroxy-2′,6′-dimethylbiphenyl-3-yl)methyl][(2-nitrophenyl)sulfonyl]amino}phenyl)propanoate (3.60 g, 5.67 mmol), 2-(ethylamino)ethanol (0.61 mL, 6.24 mmol) and tributylphosphine (2.26 mL, 8.51 mmol) in tetrahydrofuran (100 mL) was added 1,1′-(azodicarbonyl)dipiperidine (2.21 g, 8.53 mmol) under stirring at room temperature, and the mixture was stirred for 16 hr. The resulting precipitate was filtered off, and the filtrate was concentrated under reduced pressure. The residue was subjected to silica gel column chromatography (hexane/ethyl acetate=5/1-hexane/ethyl acetate=1/3) to give a mixture (6.11 g) of tert-butyl 3-(4-{({4′-[2-(ethylamino)ethoxy]-2′,6′-dimethylbiphenyl-3-yl}methyl)[(2-nitrophenyl)sulfonyl]amino}-2-fluorophenyl)propanoate and tributylphosphine oxide as a yellow oil. To a solution of the obtained oil (0.57 g) in pyridine (3 mL) were added 2-methylpropanoyl chloride (0.17 mL, 1.62 mmol) and a small amount of N,N-dimethylpyridine-4-amine under stirring at room temperature, and the mixture was stirred for 1 hr. The reaction mixture was concentrated under reduced pressure, and the residue was partitioned between ethyl acetate and saturated aqueous sodium hydrogencarbonate, and the mixture was extracted with ethyl acetate. The organic layer was dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The obtained residue was purified by silica gel column chromatography (hexane/ethyl acetate=10/1-hexane/ethyl acetate=2/5) to give the title compound (0.35 g) as a colorless oil.

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