Abstract Optically active terpene such as (R)-(+)-citronellol,(R)-(+)-pulegone or (S)-ar- turmerone is prepared in high enantiomeric excess from an intermediate,(R)-(+)-citronellic acid or (S)-(+)-3-p-tolylbutyric acid, which is easily prepared by the S n 2 type of ring opening reaction of (R)-(+)-β-methyl-β-propiolactone with homoprenylmagnesium bromide in the presence of a copper (I) salt or di-p-tolylcuprate.
