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0 °C

1-(2,4-Dihydroxy-3-propylphenyl)-2,2,2-trifluoroethanone oxime (prepared by the method described in WO 97/28137, 4.2 g, 15.96 mmol) and triphenylphosphine (8.82 g, 33.6 mmol) were dissolved in THF (250 mL) and the mixture was cooled to 0° C. A solution of diethyl azodicarboxylate (5.02 mL, 32.0 mmol) in THF (150 mL) was then slowly added over a period of 30 minutes. The reaction mixture was stirred for 1 h at 0° C. After addition of water (500 mL), the aqueous layer was extracted with ethyl acetate. The combined organic layers were washed with brine and dried over sodium sulfate. The solvent was removed in vacuo and the product purified via silica gel flash chromatography (ethyl acetate/hexane (v/v)=1:6). The product was obtained as a white-yellow powder in a yield of 1.96 g (8.0 mmol, 50%). 1H NMR (300 MHz, CDCl3) δ 1.00 (t, 3H), 1.73 (m, 2H), 2.88 (t, 2H), 5.34 (s, 1H), 6.93 (d, 1H), 7.48 (d, 1H).

1. extractionthe aqueous layer was extracted with ethyl acetate
2. washThe combined organic layers were washed with brine
3. dry with materialdried over sodium sulfate
4. customThe solvent was removed in vacuo
5. customthe product purified via silica gel flash chromatography (ethyl acetate/hexane (v/v)=1:6)
6. customThe product was obtained as a white-yellow powder in a yield of 1.96 g (8.0 mmol, 50%)