Funk Timothy W, Berlin Jacob M, Grubbs Robert H
Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
J Am Chem Soc. 2006 Feb 15;128(6):1840-6. doi: 10.1021/ja055994d.
The synthesis of olefin metathesis catalysts containing chiral, monodentate N-heterocyclic carbenes and their application to asymmetric ring-closing metathesis (ARCM) are reported. These catalysts retain the high levels of reactivity found in the related achiral variants (1a and 1b). Using the parent chiral catalysts 2a and 2b and derivatives that contain steric bulk in the meta positions of the N-bound aryl rings (catalysts 3-5), five- through seven-membered rings were formed in up to 92% ee. The addition of sodium iodide to catalysts 2a-4a (to form 2b-4b in situ) caused a dramatic increase in enantioselectivity for many substrates. Catalyst 5a, which gave high enantiomeric excesses for certain substrates without the addition of NaI, could be used in loadings of < or =1 mol %. Mechanistic explanations for the large sodium iodide effect as well as possible mechanistic pathways leading to the observed products are discussed.
报道了含有手性单齿N-杂环卡宾的烯烃复分解催化剂的合成及其在不对称闭环复分解反应（ARCM）中的应用。这些催化剂保留了相关非手性变体（1a和1b）中发现的高反应活性。使用母体手性催化剂2a和2b以及在与氮相连的芳基环的间位含有空间位阻的衍生物（催化剂3 - 5），五元至七元环的形成对映体过量率高达92%。向催化剂2a - 4a中加入碘化钠（原位形成2b - 4b），对许多底物的对映选择性有显著提高。对于某些底物，在不添加NaI时能给出高对映体过量的催化剂5a，其用量可低至或等于1 mol%。讨论了碘化钠的显著效应的机理解释以及导致观察到的产物的可能机理途径。
