Why do thioureas and squaramides slow down the Ireland-Claisen rearrangement?,Beilstein Journal of Organic Chemistry

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Why do thioureas and squaramides slow down the Ireland-Claisen rearrangement?
Beilstein Journal of Organic Chemistry ( IF 2.2 ) Pub Date : 2019-12-10 , DOI: 10.3762/bjoc.15.290
Dominika Krištofíková ₁ , Juraj Filo ₂ , Mária Mečiarová ₁ , Radovan Šebesta ₁

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A range of chiral hydrogen-bond-donating organocatalysts was tested in the Ireland-Claisen rearrangement of silyl ketene acetals. None of these organocatalysts was able to impart any enantioselectivity on the rearrangements. Furthermore, these organocatalysts slowed down the Ireland-Claisen rearrangement in comparison to an uncatalyzed reaction. The catalyst-free reaction proceeded well in green solvents or without any solvent. DFT calculations showed that the activation barriers are higher for reactions involving hydrogen-donating organocatalysts and kinetic experiments suggest that the catalysts bind stronger to the starting silyl ketene acetals than to transition structures thus leading to inefficient rearrangement reactions.

中文翻译：

为什么硫脲和方胺会减缓爱尔兰-克莱森的重排？

在甲硅烷基乙烯酮缩醛的爱尔兰-克莱森重排中测试了一系列手性给氢键的有机催化剂。这些有机催化剂均不能在重排上赋予任何对映选择性。此外，与未催化反应相比，这些有机催化剂减缓了爱尔兰-克莱森重排。在绿色溶剂中或没有任何溶剂的情况下，无催化剂的反应进展顺利。DFT计算表明，涉及供氢有机催化剂的反应的活化能垒较高，动力学实验表明，催化剂与起始甲硅烷基乙烯酮缩醛的结合力强于过渡结构，从而导致重排反应效率低下。

更新日期：2019-12-11

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