PURPOSE: To obtain a chiral epoxybutyrate in high yield by reacting a γ-lactone with an alkoxide, which is useful as a synthetic intermediate for 1-carba-1-dethia cephem series antibiotics.

CONSTITUTION: A γ-lactone of formula I (R1 is a 1-6C alkyl, trifluoromethyl, benzyl, phenyl or tolyl) is reacted with an alkoxide of the formula RO- (R is the hydrocarbyl residue of a 1-8C alcohol) in the presence of an alcohol of the formula ROH under substantially anhydrous conditions at -60 to 0°C, thereby to obtain a chiral epoxybutyrate of formula II. The alkoxide is used in at least one equivalent, preferably 1.0-1.2 equivalents, and the alcohol is used in 10-200 equivalents to the lactone. The compound of the formula I is new and is obtained by sulfonylation of a chiral dihydroxyfuranone of formula III with a sulfonyl halide.