A NEW RESOLUTION PROCEDURE FOR THE PREPARATION OF BOTH (R)-(+)-4-TERT-BUTOXYCYCLOPENT-2-ENONE AND (S)-(-)-4-TERT-BUTOXYCYCLOPENT-2-ENONE FROM RACEMIC 4-TERT-BUTOXYCYCLOPENT-2-ENONE AND CONVERSION OF (R)-(+)-4-TERT-BUTOXYCYCLOPENT-2-ENONE INTO (R)-(+)-4-ACETOXYCYCLOPENT-2-ENONE - A NEW METHOD FOR THE DETERMINATION OF THE ENANTIOMERIC PURITIES OF THE RESOLVED ENONES

(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,R(S))-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 greater-than-or-equal-to 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 greater-than-or-equal-to 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 H-1 NMR spectroscopy.