[Na].[C:2]([O:10][CH2:11][CH3:12])(=[O:9])[CH2:3][C:4]([O:6][CH2:7][CH3:8])=[O:5].[O-]CC.[Na+:16].Br[CH:18]([CH2:20][CH2:21][CH3:22])[CH3:19]>C(O)C>[O-:5][CH2:4][CH3:3].[Na+:16].[CH3:19][CH:18]([CH:3]([C:4]([O:6][CH2:7][CH3:8])=[O:5])[C:2]([O:10][CH2:11][CH3:12])=[O:9])[CH2:20][CH2:21][CH3:22]Sodium ethoxide was prepared from sodium metal (7.61 g) and absolute ethanol (200 ml). Diethyl malonate (50.3 ml) was added dropwise to the ethanol containing sodium ethoxide. After heating to 80° C., 2-bromopentane (50 g) was added and the mixture was reflued for 24 h. Diethyl (2-pentyl)malonate (62.7 g) was obtained after the usual work-up. Diethyl (2-pentyl)malonate was added to a 50% potassium hydroxide solution and the mixture was heated for 3 h while water/ethanol being distilled off. After cooling, the solution was acidified with concentrated hydrochloric acid. Then, the solution was extracted with ethyl acetate. The extract was concentrated under reduced pressure, and the resulting product was heated to 180° C. until bubbling ceased. After distillation, colorless 3R,S-methy-caproic acid was obtained. Yield: 27.7 g (35%), b.p. 200° C./760 mmHg.
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