Synthesis of trifluoromethyl cyclohexyl, cyclohexenyl and aryl compounds via stepwise Robinson annulation
作者:Fabien Massicot、Alex Mor Iriarte、Thierry Brigaud、Aurélien Lebrun、Charles Portella
DOI:10.1039/c0ob00518e
日期:——
The diketone 2-fluoro-2-(trifluoromethyl)-1-phenylhexane-1,5-dione 3 was synthesized by a Mukaiyama Michael type reaction from the corresponding tetrafluoroenol silyl ether prepared from pentafluoropropiophenone. This diketone was treated under basic conditions and was converted, depending on the stoichiometry of the base, into the surprisingly stable ketol 4-fluoro-4-(trifluoromethyl)-3-hydroxy-3-phenylcyclohexanone 4 as a single diastereomer (catalytic KOH) or to the biphenylol 6-(trifluoromethyl)biphenyl-3-ol (excess KOH, THF) 5. Solvolysis of the trifluoromethyl group (anionic activation) occurred using excess KOH in alcohol. The corresponding cyclohexenone derivative 7, the usual product of Robinson annulation, might be prepared in good yield via mesylation of the ketol. Thus various unprecedented fluorinated cyclohexane and aromatic derivatives were achieved in a few steps from the commercially available pentafluoropropiophenone.
二酮化合物2-氟-2-(三氟甲基)-1-苯基己烷-1,5-二酮3是通过Mukaiyama Michael反应合成的,反应物为从五氟丙酮酮准备的四氟醇硅醚。该二酮在碱性条件下处理后,根据碱的化学计量,可以转化为出人意料的稳定酮醇4-氟-4-(三氟甲基)-3-羟基-3-苯基环己酮4,作为单一的立体异构体(催化KOH),或者转化为联苯醇6-(三氟甲基)联苯-3-醇(过量KOH,THF)5。使用过量KOH在醇中对三氟甲基的溶剂解离(阴离子活化)发生。相应的环己烯酮衍生物7,作为Robinson缩合的常见产物,可通过对酮醇的梅磷化获得良好的产率。因此,从商业可得的五氟丙酮酮出发,仅需几步即可获得多种前所未有的氟化环己烷和芳香衍生物。