Chemoselectivity as a delineator of cuprate structure in catalytic 1,4-addition of diorganozinc reagents to Michael acceptors.
Chemoselectivity as a delineator of cuprate structure in catalytic 1,4-addition of diorganozinc reagents to Michael acceptors.
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DOI：
10.1002/chem.200903310
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发表时间：
2010-05
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影响因子：
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通讯作者：
M. Welker;S. Woodward;L. Veiros;M. J. Calhorda
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文献类型：
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作者：
M. Welker;S. Woodward;L. Veiros;M. J. Calhorda
环硫缩醛（RS）(2)CHCHO [R=1/2 x -(CH(2))(3)-]与HCCCOMe反应，然后用TsCl/DABCO （Ts=tosyl， DABCO=1,4-重氮杂环[2.2.2]辛烷）处理，得到单保护的1,4-苯并醌二硫缩醛。用手性磷酰胺配体将sr保护的1,4-苯醌与类似or保护的缩醛在铜催化ZnMe(2)的加成反应性进行了比较。在两种CuX(2)预催化剂（X=OAc, 12.2 kcal mol(-1)）下，测定了后一种or缩醛与ZnMe(2) （>95% ee）的1,4甲基化活化能；X=OTf， 6.7千卡摩尔（-1）；Tf = triflate)。二硫缩醛SR在Cu(I)/ZnMe(2)存在下芳构化，通过C-S键生成1,4- hoc (6)H(4)S(CH(2))(3)SMe。这两种非常密切相关的底物的不同行为与密切相关的铜中间体的形成一致，这些中间体通过DFT计算优化，支持合成和动力学研究，从而定义了这两种途径的机制。
Reaction of the cyclic thioacetal (RS)(2)CHCHO [R=1/2 x -(CH(2))(3)-] with HCCCOMe, followed by treatment with TsCl/DABCO (Ts=tosyl, DABCO=1,4-diazabicyclo[2.2.2]octane) affords the mono-protected 1,4-benzoquinone dithioacetal. The reactivity of this SR-protected 1,4-benzoquinone has been compared with the behavior of the analogous OR-protected acetal in copper-catalyzed additions of ZnMe(2) by using chiral phosphoramidite ligands. The activation energy for 1,4-methylation of the latter OR-acetals with ZnMe(2) (>95% ee) has been determined for two CuX(2) pre-catalysts (X=OAc, 12.2 kcal mol(-1); X=OTf, 6.7 kcal mol(-1); Tf=triflate). The dithioacetal SR aromatizes in the presence of Cu(I)/ZnMe(2) giving 1,4-HOC(6)H(4)S(CH(2))(3)SMe through C-S bond formation. The disparate behavior of these two very closely related substrates is in accordance with the formation of closely related cuprate intermediates that were optimized by DFT calculations, supporting the synthetic and kinetic studies and thus defining the mechanisms of both pathways.