Recent Advances in N-Heterocyclic Carbene Catalyzed Oxidative Cyclization for the Formation of Heterocycles

Oxidative N-heterocyclic carbene catalyst mediated cyclization proved to be an efficient strategy for the construction of various N- and O- heterocycles. Among several metal-free methods available for the construction of heterocyclic compounds, oxidative NHC catalysis proved to be an elegant and efficient strategy as several enantioenriched compounds with excellent enantioselectivities can be synthesized in good yields. The most common method of the generation of these heterocycles proceeds via the commonly encountered intermediate in oxidative NHC catalysis (i. e.) acyl azolium intermediate. This intermediate proves to be the active species as it can undergo reaction with suitable substrates leading to the formation of numerous N- and O- heterocycles. Herein, recent reports on different strategies that enable formal [2+2], [3+2], [3+3], [4+2] or [4+3] annulations between the incoming substrates and acyl azolium species or other active intermediates which can add to suitable substrate leading to various heterocycles were summarized.

Automated summary

Oxidative N-heterocyclic carbene-catalyzed cyclization is an efficient strategy for constructing various N- and O-heterocycles with excellent enantioselectivities. The reaction proceeds via an acyl azolium intermediate, which is an active species capable of forming a diverse array of heterocycles through reactions with suitable substrates. Recent reports have summarized different strategies for formal annulations between incoming substrates and acyl azolium or other active intermediates, leading to the formation of various heterocycles.