Regioselective C3-N alkylation of coumarins under solvent-free conditions: a graphene oxide nanosheet promoted novel strategy for C-N bond formation via azide-alkene 1,3-dipolar cycloaddition reaction

A carbocatalytic, regioselective synthesis of C₃-N alkylated coumarins has been reported under solvent-free conditions. This synthetic protocol provides a series of C₃-N alkylated coumarins in good yields starting directly from coumarins and azides in the presence of GO nanosheets without any additives or ligands needed. In contrast to the frequently applied synthetic strategy that involves nucleophilic substitution of benzylamine/benzyl alcohol with halogenated coumarins in the presence of Pd or Cu catalyst for the generation of N-alkylated coumarins, here, coumarins directly reacts with azides via azide-alkene 1,3-dipolar cycloaddition/ring cleavage/1,2-H migration/denitrogenation, followed by 1,3-H migration to afford C₃-N alkylated coumarins.