Isobutyric Acid → Allyl 1-{[(alpha-Isobutanoyloxyethoxy)carbonyl]aminomethyl}-1-Cyclohexane Acetate

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A solution of compound (14) (38 g, 0.12 mol) in isobutyric acid (55 mL, 52.5 g, 0.6 mol) was added to a mixture of isobutyric acid (55 mL, 52.5 g, 0.6 mol) in N-methylmorpholine (65 mL, 60 g, 0.59 mol) at 0° C. over a period of 30 min. The resulting turbid solution was stirred for 16 h at room temperature. The reaction mixture was diluted with diethyl ether (500 mL) and washed with water (3×200 mL) followed by 10% potassium bicarbonate (4×200 mL) and brine (200 mL). The organic phase was dried over anhydrous sodium sulfate and concentrated to yield a viscous liquid. This crude product was purified by column chromatography on silica gel, eluting with 7.5% ethyl acetate:hexane to give the desired compound (15) as a clear, viscous liquid (37 g, 84% yield). 1H NMR (CDCl3, 400 MHz): δ 1.15 (d, 6H), 1.35-1.58 (m, 10H), 2.31 (s, 2H), 2.51 (m, 1H), 3.19 (d, 2H), 4.56 (d, 2H), 5.24 (dd, 1H), 5.32 (dd, 1H), 5.35 (br. s, 1H), 5.84-5.94 (m, 1H), 6.78 (q, 1H). MS (ESI) m/z 392.24 (M+H+).

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