Methanol → Methyl 3-[(2S)-oxiran-2-yl]propanoate

28% Sodium methoxide/MeOH solution (74.0 g, 383.35 mmol) was added to a mixture of (S)-(5-oxotetrahydrofuran-2-yl)methyl 4-methylbenzenesulfonate (51.81 g, 191.67 mmol) and dehydrated MeOH (280 mL) at room temperature, and the mixture was stirred at room temperature for 1.5 hr. The reaction mixture was cooled under ice-cooling, and the mixture was neutralized with acetic acid (about 15 mL). The reaction mixture was concentrated to about half-volume under reduced pressure, and ice water (350 mL) was added thereto. Then, the mixture was extracted with a mixed solvent of ethyl acetate/diethyl ether (3:1) (×3). The organic layer was washed successively with aqueous sodium hydrogencarbonate solution, water and brine, and dried over magnesium sulfate, and the solvent was evaporated under reduced pressure to give crude methyl (S)-3-(oxiran-2-yl)propanoate (13.12 g, 101 mmol, 53%) as a colorless oil.