Catalysis-Controlled Selective N-mono or N-di-methylation of Anilines: A Review on Synthesis of N-methyl or N,N-dimethyl anilines

N-alkyl anilines are a series of common and versatile compounds which not only have been used as reaction solvents, acid-accepters, and organic-bases, but also in synthesis of dyes, pharmaceuticals, and anti-colodal. The N-methyl and/or N,N-dimethyl anilines are the most representative ones among these. Due to their widespread uses, numerous works have been reported on synthetic strategies in the past decades. The studies on N−H methylations of anilines mainly focus on selection of reagents, selection of catalysts, or ligands design. Different transition-metals, e. g., Ir, Ru, Pd, and et. al, with different ligands have been used in the methylation protocols. Methanol (CH₃OH), carbon dioxide (CO₂), formaldehyde (HCHO), or dimethyl carbonate ((CH₃)₂CO₃) was used as C source, and hydrogen (H₂) or silanes as H source. In this work, we would like to summarize the latest advances on the synthesis of N-methyl (N,N-dimethyl included) anilines and derivatives. This review provides an overview of reactants and catalyst, as well as an emphasis on the scope of substrates and proposed reaction mechanism for each work.