Reactions of Aliphatic Ketones R2CO (R=Me, Et,iPr, andtBu) with the MCl4/Li(Hg) System (M=U or Ti): Mechanistic Analogies between the McMurry, Wittig, and Clemmensen Reactions
作者:Claude Villiers、Michel Ephritikhine
DOI:10.1002/1521-3765(20010716)7:14<3043::aid-chem3043>3.0.co;2-d
日期:2001.7.16
system (M = U, Ti) at 20 degrees C revealed significant differences. For R = Me, the reaction proceeded exclusively (M = U) or preferentially (M = Ti) via a metallopinacol intermediate resulting from dimerization of ketyl radicals. Pinacol was liberated by hydrolysis, and tetramethylethylene was obtained after further reduction at 65 degrees C. For R=iPr, formation of iPr2C=CiPr2 as the only coupling
酮R2CO(R = Me,Et,iPr,tBu)与MCl4 / Li(Hg)系统(M = U,Ti)在20摄氏度下反应的产物分析显示出显着差异。对于R = Me,反应仅通过(由酮基的二聚化产生的)金属麦草醇中间体进行(M = U)或优选地(M = Ti)进行。通过水解释放出频哪醇,并在65℃进一步还原后获得四甲基乙烯。对于R = iPr,形成iPr2C = CiPr2作为唯一的偶联产物,该烯烃不通过还原松果磺酸铀[U] -OCR2CR2O来生产-[U](R = iPr)在20摄氏度时,相应的松果酸钛对松碳CC键断裂的不稳定性表明,iPr2CO的还原偶联并未通过酮基的二聚作用进行。2的形成 4-二甲基-2-戊烯有利于酮基的脱氧还原而产生的类胡萝卜素中间体。这些结果表明,对于位阻酮,McMurry反应可以看作是类似Wittig的烯化反应。对于R = tBu,没有获得偶联产物,并且烷烃tBu2CH2是主要产物。类胡萝卜素物质[M]