Addition, Substitution, and Ring-Contraction Reactions of Quinones with N-Heterocyclic Carbenes

N-Heterocyclic Carbenes and N-Heterocycles as Synthetic Reagents and Building Blocks

N-Heterocyclic carbenes (NHCs) have become important tools in modern synthetic chemistry due to their versatility as organocatalysts and ligands in organometallic complexes. Since their first isolation and characterization, NHCs have demonstrated significant utility in various catalytic processes, offering advantages such as strong σ-electron donation and the ability to stabilize reactive intermediates. However, beyond their well-documented roles in catalysis, the potential of NHCs as stoichiometric reagents and synthetic building blocks remains an underexplored yet promising area. This Mini-review aims to shed light on these lesser-known applications of NHCs and their N-heterocyclic precursors or derivatives in organic synthesis. Furthermore, we discuss how the unique electronic and steric properties of NHCs can be harnessed to develop new synthetic methodologies or construct interesting organic frameworks. By highlighting these emerging uses, we hope to encourage further research into the non-catalytic applications of NHCs, broadening their scope and impact in synthetic chemistry.

N-Heterocyclic carbene based catalytic platform for Hauser-Kraus annulations

The venerable Hauser–Kraus annulation is an effective and convergent method for generating oxygenated polycyclic aromatic compounds. Despite its application in complex molecule synthesis, the harsh and strongly basic conditions can limit its utility in more functionalized molecular settings. We have developed the first catalytic Hauser–Kraus annulation based on N-heterocyclic carbene catalysis that proceeds under milder conditions. We demonstrate the scope of the transformation in the presence of several functional groups. We also propose a concerted mechanism for the annulation that proceeds through a non-canonical Breslow intermediate.

The venerable Hauser–Kraus annulation is an effective and convergent method for generating oxygenated polycyclic aromatic compounds. A catalytic Hauser–Kraus annulation has been developed based on N-heterocyclic carbene catalysis.