There are provided novel and optically active 2,2-dimethyl-1,3-dioxin-4-ones which are useful as starting materials for physiologically active compounds, functional materials or the like. Provided are optically active 5,6-epoxyhexanoic acid esters and novel optically active 6-substituted tetrahydropyran-2-one derivatives. That is, optically active 6-chloromethyltetrahydropyran-2-one can be synthesized by lactonizing optically active 2,2-dimethyl-6-(3-chloro-2-hydroxypropyl)-1,3-dioxin-4-one to form optically active 6-chloromethyltetrahydropyran-2,4-dione; reacting the thus formed compound with hydrogen in the presence of a catalyst to obtain optically active 6-chloromethyl-4-hydroxytetrahydropyran-2-one; subjecting this compound to a dehydration reaction, thereby obtaining optically active 6-chloromethyldihydropyran-2-one; reacting this compound with hydrogen in the presence of a catalyst to form optically active 6-chloromethyltetrahydropyran-2-one; and then treating this compound under basic conditions to prepare an optically active 5,6-epoxyhexanoic acid ester represented by the formula (6) ##STR1## (wherein the symbol * represents an asymmetric carbon atom, and R is a methyl group or an ethyl group).