N-Heterocyclic Carbene Catalyzed Benzannulations: Mechanism and Synthetic Utility

Aromatic compounds are ubiquitous in pharmaceutical agents and other functional materials. Therefore, synthetic methods to construct highly functionalized aromatic frameworks have attracted considerable attention, especially when utilizing acyclic precursors instead of pre-existing benzenoid cores. A plethora of methods exist in the literature for the construction of substituted aromatic products by using transition metal catalysis and base-promoted benzannulation reactions starting from acyclic precursors. In recent years, organocatalytic approaches such as N-heterocyclic carbene catalysis have emerged as effective tools for the efficient and regioselective construction of highly functionalized aryl rings under metal-free and mild reaction conditions. The fundamental objective of this minireview is to highlight the synthetic potential of NHC-catalyzed benzannulations for the generation of aromatic rings with complex substitution patterns and to discuss these reactions from the perspective of their mechanistic design.