Catalysis using N-heterocyclic carbenes (NHCs) has been widely employed for the umpolung of aldehydes, and these reactions proceed via the generation of nucleophilic Breslow intermediates. These acyl anion equivalents can be added to aldehydes, ketones, imines, Michael acceptors, and even unactivated carbon–carbon multiple bonds. In a majority of the cases, aromatic aldehydes are used in NHC catalysis. However, the use of aliphatic aldehydes is relatively less explored because of the low electrophilicity of the aliphatic aldehydes compared to aromatic aldehydes for the nucleophilic addition of carbenes, and the presence of α-acidic protons leading to side reactions under basic conditions. There are several NHC-catalyzed reactions that engage aliphatic aldehydes, and this Highlight summarizes the advances in NHC catalysis using aliphatic aldehydes as substrates.

中文翻译：

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使用脂族醛的N-杂环卡宾（NHC）有机催化

使用N-杂环卡宾（NHC）的催化已广泛用于醛的缩酮反应，这些反应通过亲核Breslow中间体的产生。这些酰基阴离子当量可以添加到醛，酮，亚胺，迈克尔受体，甚至未活化的碳-碳多键中。在大多数情况下，芳族醛用于NHC催化。然而，相对而言，由于相对于芳族醛而言，与芳族醛相比，脂族醛的亲电性较低，因此脂肪族醛的亲电性较低，而且α-酸性质子的存在导致在碱性条件下发生副反应。有几种NHC催化的反应会与脂族醛发生反应，本要点总结了使用脂族醛作为底物进行NHC催化的进展。