New insights into addition reactions of dialkylzinc reagents to trifluoromethyl ketones: structural authentication of a beta-hydride elimination product containing a tetranuclear zinc chain.
New insights into addition reactions of dialkylzinc reagents to trifluoromethyl ketones: structural authentication of a beta-hydride elimination product containing a tetranuclear zinc chain.
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二烷基锌试剂与三氟甲基酮的加成反应的新见解：含有四核锌链的β-氢化物消除产物的结构鉴定。
DOI：
10.1039/b911818g
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发表时间：
2010
影响因子：
4
通讯作者：
Matthew D. McCall
中科院分区：
文献类型：
--
作者：
Eva Hevia;A. Kennedy;J. Klett;Zoe Livingstone;Matthew D. McCall
本文用（1）H和（19）F NMR谱研究了2，2，2-三氟苯乙酮1与[ZnR（2）（TMEDA）]（R= Me，Et，（t）Bu，CH（2）SiMe（3）; TMEDA= N，N，N '，N'-四甲基乙二胺）的化学计量烷基化反应。对于R = Me，Et，烷基化产物烷基（醇盐）[（TMEDA）Zn（R）{OC（CF（3））（R）Ph}]（R = Me，2：Et，3）作为反应的单一产物获得。当二烷基锌试剂的空间体积增加时，烷基化反应被抑制。因此，对于R =（t）Bu，还原产物[（TMEDA）Zn（（t）Bu）{OC（CF（3））（H）Ph}]作为从有机金属试剂的（t）Bu基团之一消除β-氢化物的结果而获得。(1)H反应的NMR光谱监测允许检测作为该还原过程的副产物的异丁烯。对于在β位缺少氢原子的高度空间要求的基团R = CH（2）SiMe（3），即使在无氧条件下也没有观察到反应。这些反应中的两个重要中间体已在结构上得到了阐明：[（TMEDA）Zn（Me）{OC（CF（3））（Me）Ph}]（2），其可能参与先前报道的由TMEDA催化的ZnR（2）的三氟甲基酮的烷基化反应;以及前所未有的四核[（（t）Bu）（2）Zn（4）{OC（CF（3））（H）Ph}（6）]（5），其由1与（t）Bu（2）Zn，其显示出稀有的Zn。锌...锌...烷基锌（烷氧基）的Zn直链排列。
A systematic study of the stoichiometric alkylation reactions of 2,2,2-trifluoroacetophenone 1 with [ZnR(2)(TMEDA)] (R= Me, Et, (t)Bu, CH(2)SiMe(3); TMEDA= N,N,N',N'-tetramethylethylenediamine) monitored by (1)H and (19)F NMR spectroscopy is presented. For R = Me, Et the alkylation products alkyl(alkoxides) [(TMEDA)Zn(R){OC(CF(3))(R)Ph}] (R = Me, 2: Et, 3) are obtained as the single products of the reaction. When the steric bulk of the dialkylzinc reagent is increased the alkylation reaction is inhibited. Thus, for R = (t)Bu, the reduction product [(TMEDA)Zn((t)Bu){OC(CF(3))(H)Ph}] is obtained as a result of beta-hydride elimination from one of the (t)Bu groups of the organometallic reagent. (1)H NMR spectroscopic monitoring of the reaction allowed the detection of isobutene as a side product of this reduction process. For the highly sterically demanding group R = CH(2)SiMe(3) which lacks hydrogen atoms at the beta position, no reaction is observed even under refluxing conditions. Two important intermediates from these reactions have been structurally elucidated: [(TMEDA)Zn(Me){OC(CF(3))(Me)Ph}] (2) which could be involved in the previously reported alkylation reaction of trifluoromethyl ketones by ZnR(2) catalysed by TMEDA and unprecedented tetranuclear [((t)Bu)(2)Zn(4){OC(CF(3))(H)Ph}(6)] (5) resulting from the reduction of 1 when reacted with (t)Bu(2)Zn, which displays a rare Zn...Zn...Zn...Zn linear chain arrangement for a zinc alkyl(alkoxide).