N-Methylation of Aromatic Amines and N-Heterocycles under Acidic Conditions with the TTT (1,3,5-Trioxane–Triethylsilane–Trifluoroacetic Acid) System

A novel reductive N-methylation protocol under acidic conditions with the TTT (1,3,5-trioxane–triethylsilane–trifluoroacetic acid) system is disclosed. This method is highly specific for aromatic amines and several N-heterocycles (indoles and annulated analogues, phenoxazine, phenothiazine), insensitive to steric hindrance, and compatible with a wide range of functional groups. Further the N-methylation step can be combined with an in situ N-Boc deprotection. Compounds in which the nucleophilicity of the NH group is eliminated by protonation under the reaction conditions (aliphatic amines, azaarenes of noteworthy basicity) are inert. In several examples, it was demonstrated that the TTT system is complementary to other N-methylation protocols.