A new resolution procedure for the preparation of both (R)-(+)- 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
作者:Bart M. Eschler、Richard K. Haynes、Michael D. Ironside、Steve Kremmydas、Damon D. Ridley、Trevor W. Hambley
DOI:10.1021/jo00015a035
日期:1991.7
(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.
(1S)-(-)-10-巯基异冰片在含有N,N,N',N'-四甲基乙二胺的甲醇中与(+/-)-4-叔丁氧基环戊-2-烯酮发生共轭加成,得到3-叔丁氧基-4-[[(exo-2'-羟基-7',7'-二甲基双环[2.2.1]庚烷基)甲基]硫代]环戊酮的两种异构体(1:1比例)的混合物,收率93-95%。该混合物在过氯苯甲酸作用下转化为相应的硫氧化物混合物。通过X射线晶体学确定了绝对构型的(3R,4R,R(S))-硫氧化物异构体从该混合物中以76%的手性收率析出。在二氧化硅胶上分解此硫氧化物可得到(R)-(+)-4-叔丁氧基环戊-2-烯酮(手性纯度≥99.9%),以及10-硫二异冰片-10'-硫氧化物,产率为92%。同样,(S)-(-)-烯酮可由(1R)-(+)-10-巯基异冰片制得。在醋酐中添加催化量的FeCl3,(±)-和(R)-(+)-烯酮分别转化为(+/-)-和(R)-(+)-4-乙酰氧基环戊-2-烯酮(手性纯度≥99.9%),收率为80%。产物的手性纯度通过与(-)-10-巯基异冰片的处理及其加成物的HPLC和400 MHz H-1 NMR光谱分析确定。