Solution-Phase and Mechanochemical Brønsted-Acid-Catalyzed N-Alkylation of NH-Heterocycles via Hydroamination of Vinyl Ethers

A Brønsted-acid-catalyzed hydroamination of vinyl ethers with carbazoles was developed using diphenyl hydrogen phosphate (DPHP) as the catalyst. The method enables the efficient, regioselective N-alkylation of various carbazoles and NH-heterocycles under mild conditions. Mechanistic studies indicate bifunctional activation through hydrogen bonding and cation-π interactions. The reaction was also adapted to mechanochemical conditions for a greener process. While attempts at enantioselective hydroamination have met with limited success, this approach provides a practical and sustainable route to N-alkylated heterocycles.