C[O-].[Na+].[C:4]([O:12][CH2:13][CH3:14])(=[O:11])[CH2:5][C:6]([O:8][CH2:9][CH3:10])=[O:7].CS(O[C@@H:20]([CH3:25])[CH2:21][CH2:22][CH2:23][CH3:24])(=O)=O.[Cl-].[NH4+]>CO.C(Cl)Cl>[CH3:25][C@@H:20]([CH:5]([C:6]([O:8][CH2:9][CH3:10])=[O:7])[C:4]([O:12][CH2:13][CH3:14])=[O:11])[CH2:21][CH2:22][CH2:23][CH3:24]At room temperature, 28.9 g of sodium methoxide (95% pure, 0.51 mol) were dissolved in 150 ml of dry methanol under protective nitrogen gas in a three-neck flask with internal thermometer, dropping funnel and stirrer. Subsequently, 85.3 g of diethyl malonate (0.533 mol) were added dropwise at from 30 to 35° C., in the course of which a suspension initially formed and dissolved toward the end of the addition. The clear mixture was stirred at 50° C. for 60 min and 80 g of (S)-1-methylpentyl methanesulfonate (0.444 mol) were added undiluted. The mixture was heated to 66° C. and stirred for 6 h. After cooling to 25° C., the suspension was admixed with 400 ml of methylene chloride and 300 ml of 5% by weight ammonium chloride solution. After phase separation, the organic phase was washed with 100 ml of water and then dried over sodium sulfate. After distillative removal of solvent, diethyl [(R)-1-methylpentyl]malonate was obtained in a yield of 94 g. The product comprises dimethyl ester and ethyl methyl ester, formed by transesterification, and unconverted malonic ester. The corrected yield is 84% of theory.
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