Mukaiyama Aldol Reactions Catalyzed by Zirconocene Bis(triflate) Complexes: Stereochemistry and Mechanisms for C−C Bond Formation
Mukaiyama Aldol Reactions Catalyzed by Zirconocene Bis(triflate) Complexes: Stereochemistry and Mechanisms for C−C Bond Formation
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DOI：
10.1021/jo971803g
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发表时间：
1998-02
影响因子：
3.6
通讯作者：
Shuqiong Lin;G. V. Bondar;C. J. Levy;S. Collins
中科院分区：
文献类型：
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作者：
Shuqiong Lin;G. V. Bondar;C. J. Levy;S. Collins
研究了Cp2Zr(OTf)2·THF或Cp2Zr(OTf)2在多种溶剂中催化α-和β-(苄氧基)醛与烯醇硅烷的醇醛缩合反应。这些反应的简单非对映选择性是适度的并且与使用具有相似空间要求的简单醛所观察到的结果相当。研究表明，二茂锆催化剂与烯醇式硅烷在硝基烷溶剂中直接反应生成TMSOTf，或者在二氯甲烷溶液中催化生成TMSOTf。尽管已知 TMSOTf 在这些条件下催化交叉羟醛反应，但该过程的速率并不总是与使用二茂锆催化剂观察到的速率具有竞争力。特别是，基于Zr介导的反应和Si介导的反应之间的速率差异以及交叉型实验中烯醇硅烷/三氟甲磺酸硅酯反应性的差异，空间无阻碍或芳香醛通过似乎主要由Zr催化的机制进行反应。与空间位阻醛...
The aldol condensations of α- and β-(benzyloxy) aldehydes with enol silanes, catalyzed by Cp2Zr(OTf)2·THF or Cp2Zr(OTf)2, in a variety of solvents were studied. The simple diastereoselectivity of these reactions is modest and comparable to that observed using simple aldehydes of similar steric requirements. Studies have revealed that TMSOTf is directly produced on reaction with the zirconocene catalyst with the enol silane in nitroalkane solvent or is formed during catalysis in dichloromethane solution. Although TMSOTf is known to catalyze cross-aldol reactions under these conditions, the rate of this process is not always competitive with that observed using the zirconocene catalysts. In particular, sterically unhindered or aromatic aldehydes react via a mechanism that appears to be mainly Zr-catalyzed, based on both the difference in rate between Zr- and Si-mediated reactions as well as differences in enol silane/silyl triflate reactivity in crossover-type experiments. With sterically hindered aldehydes...