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A solution of (S)-4-benzyl-3-((E)-(R)-2-cyclopropylmethyl-pent-3-enoyl)-oxazolidin-2-one (3.50 g, 10.92 mmol) in tetrahydrofuran (75 mL) was cooled to 0° C. before addition of a 30% aqueous solution of hydrogen peroxide (5.8 mL, 56 mmol) and a solution of lithium hydroxide monohydrate (950 mg, 22.6 mmol) in water (37 mL). The reaction was stirred at 0° C. for 2.5 h. The reaction mixture was treated with an aqueous solution of sodium metabisulphite and stirred for 10 minutes before acidifying to pH 1 with hydrochloric acid (2 M). The mixture was extracted with ethyl acetate (3×50 mL). The extract was dried over anhydrous sodium sulfate, filtered and evaporated to give a colourless oil. The oil was purified by silica gel chromatography using iso-hexanes/ethyl acetate 7:3 to yield the title compound (1.32 g, 78%) as a colourless oil and as a mixture of 2.5:1 E/Z isomers. 1H NMR (300 MHz, CDCl3) δ 0.02-0.15 (m, 1.96H), 0.39-0.52 (m, 1.96H), 0.65-0.81 (m, 0.98H), 1.47-1.63 (m, 1.96H), 1.71 (d, J=6.7 Hz, 2.94H), 3.06-3.17 (m, 0.98H), 3.45-3.56 (m, 0.28H), 5.40-5.56 (m, 0.98H), 5.57-5.72 (m, 0.98H), 10.5-12.0 (bs, LCMS (m/z) 153.1 [M−H], Tr=1.91 min.

1. stirringstirred for 10 minutes
2. extractionThe mixture was extracted with ethyl acetate (3×50 mL)
3. dry with materialThe extract was dried over anhydrous sodium sulfate
4. filtrationfiltered
5. customevaporated
6. customto give a colourless oil
7. customThe oil was purified by silica gel chromatography