Role of base assisted proton transfer in N-heterocyclic carbene-catalyzed intermolecular Stetter reaction

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• 作者：Manjaly J. Ajitha ; Cherumuttathu H. Suresh
• 关键词：Organocatalysis ; N-Heterocyclic carbene ; Stetter reaction ; Breslow intermediate ; Density functional theory
• 刊名：Tetrahedron Letters
• 出版年：25 December, 2013
• 年：2013
• 卷：54
• 期：52
• 页码：7144-7146
• 全文大小：758 K

文摘

The mechanism of the NHC-catalyzed intermolecular Stetter reaction between benzaldehyde and cyclopropene has been investigated using the PCM-M062X/6-311++G(3df,2p)//M062X/6-31+G(d,p) level of DFT. Compared to the direct reaction, a substantial reduction in the activation free energy by 10.6-14.4 kcal/mol is observed when the reaction is performed in the presence of water, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The bases promote the proton transfer step of the reaction to yield the Breslow intermediate. An early concerted transition state has been located for the stereocontrolling C-C bond formation step (螖G^# = 26.6 kcal/mol) which is used to explain the diastereomeric ratio observed in the experiment.