Oxidative N‐Heterocyclic Carbene Catalysis

N‐Heterocyclic carbene (NHC) catalysis is a by now consolidated organocatalytic platform for a number of synthetic (asymmetric) transformations via diverse reaction modes/intermediates. In addition to the typical umpolung processes involving acyl anion/homoenolate equivalent species, implementation of protocols under oxidative conditions greatly expands the possibilities of this methodology. Oxidative NHC‐catalysis allows for oxidative and oxygenative transformations through specific manipulations of Breslow‐type species depending upon the oxidant used (external oxidant or O(2)/air), the derived NHC‐bound intermediates paving the way to non‐umpolung processes through activation of carbon atoms and heteroatoms. This review is intended to update the state of the art in oxidative NHC‐catalyzed reactions that appeared in the literature from 2014 to present, with a strong focus to crucial intermediates and their mechanistic implications.