(1S)-(-)-10-Mercaptoisoborneol undergoes conjugate addition to (±)-4-tert-butoxycyclopent-2-enone in methanol containing N,N,N′,N′-tetramethylethylenediamine to give a 1:1 mixture of diastereomers of 3-tert-butoxy-4-[[(exo-2′-hydroxy-7′,7′-dimethylbicyclo[2.2.1]heptanyl)methyl]thio]cyclopentanone in 93-95% yield. The mixture is converted by m-chloroperbenzoic acid into the corresponding sulfoxide mixture. The (3R,4R,Rs)-sulfoxide isomer, whose absolute configuration has been determined by X-ray crystallography, crystallizes cleanly from this mixture in an enantiomeric yield of 76% from the corresponding sulfide. It is decomposed on silica gel to generate (R)-(+)-4-tert-butoxycyclopent-2-enone, with an enantiomeric purity of ≥99.9% in 92% yield from the sulfoxide, and 10-thiodiisobornyl 10′-sulfoxide. Similarly, the (S)-(-)-enone is prepared from (1R)-(+)-10-mercaptoisoborneol. The (±)- and the (R)-(+)-enone, respectively, are converted by a catalytic amount of FeCl3 in acetic anhydride into (±)- and (R)-(+)-4-acetoxycyclopent-2-enone (with an enantiomeric purity of ≥99.9%) in 80% yield. The enantiomeric purity of the products was assessed through their treatment with (-)-10-mercaptoisoborneol and analysis of the adducts by HPLC and 400-MHz 1H NMR spectroscopy.