Strategies for the Synthesis of N-Arylammonium Salts

Abstract

The N-arylation of tertiary amines to provide sp3 quaternary ammonium salts is a challenge in organic chemistry. To date, no general method for such arylations has been established. Here, we summarize a variety of strategies that have been tested, starting with harsh nucleophilic aromatic substitutions, through to the use of copper catalysis and the application of strong electrophiles, such as phenyl cations and benzynes. The achievements and limitations of each method are summarized, and the challenges yet to be met in the synthesis of charged ammonium compounds are described.1 Introduction2 Alkylation of Anilines: The Menshutkin Reaction3 Arylations3.1 Nucleophilic Aromatic Substitutions by Tertiary Amines3.2 Preparation of N-Arylpyridinum Salts from Zincke and Pyrylium Salts3.3 Arylations Using Phenyl Cations3.4 Copper-Catalyzed Arylation of N-Heteroarenes3.5 Benzynes as Aryl Electrophiles4 Conclusions and Perspective