Progress in Organocatalytic Dearomatization Reactions Catalyzed by N-Heterocyclic Carbenes

Abstract

Dearomative reactions allow for concise assembly of structurally complex, highly functionalized three-dimensional molecules by breaking the plane of two-dimensional aromatic starting materials. With the growing interest in N-heterocyclic carbene (NHC) organocatalysis as a powerful strategy for synthesizing diversiform molecules, mainly by polarity-reversal (umpolung) approaches, NHC-catalyzed dearomatization reactions have recently been successfully used for the construction of the skeletons of natural products and drugs. By generating various key intermediates (i. e., Breslow intermediates, acyl azolium intermediates, homoenolate intermediates, enolate intermediates, and azolium dienolate intermediates), NHCs can readily destroy aromaticity by electrophilic or nucleophilic interactions with aromatic compounds. In this overview, progress in NHC-catalyzed dearomative reactions is summarized; the reactions are grouped according to reaction modes and categories of intermediates, and representative mechanisms are provided. This review aims to serve as a comprehensive reference for work in the emerging field of organocatalytic dearomatization.