NEW MATERIAL:An optically active acetic acid ester expressed by formula I [CH3 groups at the 1- and 4-positions are (1R,4S) or (1S,4R); R is CH2OH or COOH].

EXAMPLE: (2R,5S)-6-Hydroxy-5-methyl-2-hexyl acetate.

USE: An intermediate for synthesizing sex pheromones of carpenter bee, e.g. (2R, 5S)-2-methyl-5-hexanolide, in high optical purity in large quantities.

PREPARATION: An ester compound expressed by formulaII is converted into a compound having protected OH group, which is reduced with LiAlH4, etc. to afford a compound expressed by formula III (R1 is a protecting group). The resultant compound is then converted into a p-toluenesulfonic acid ester, which is further converted into a sulfide compound. The sulfide compound is then oxidized to give a sulfone compound, which is then reacted with an epoxide expressed by formula IV to give an alcohol compound expressed by formula V. The resultant alcohol compound expressed by formula V is then desulfurized and acetylated to afford an acetylated compound expressed by formula VI, which is deprotected to give the aimed compound expressed by formula I (R is CH2 OH).