Highly specific N-monomethylation of primary aromatic amines

Abstract A synthetic methodology for the specific conversion of primary aromatic amines into their N -monomethyl derivatives under very mild conditions is presented. Anilines are treated with 4-nitrobenzenesulfonyl (nosyl) chloride to generate the corresponding sulfonamides 2 in high yields. The subsequent N-methylation reaction of the sulfonamides 2 with a solution of diazomethane is rapid and quantitative. Removal of the nosyl protecting group is readily carried out using the reagent system mercaptoacetic acid/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) affording the N -monomethylated aromatic amines 4 . The procedure is convenient, efficient, and gives rise to the N -monomethyl-anilines exclusively.