N-alkylation Of Activated Alcohols Catalyzed By Transition Metal Iridium

The N-alkylation of amines presents one of the most fundamental and important C-N bond-forming reactions in organic synthesis.Traditionally,such transformations were performed with alkyl halides as alkylating agents in the presence of stoichiometric bases.However,this method uses more toxic haloalkanes and produces environmentally hazardous waste.In recent years,much attention has been directed to the N-alkylation of amines with alcohols as alkylating agents based on the so-called hydrogen autotransfer process or hydrogen-borrowing strategy,using transition metal catalyst.Similarly,N-methylation of amines is also an important type of reaction.N-methylated products containing N-methylation are widely used in medicine,fine chemicals and daily necessities.However,based on the automatic hydrogen transfer mechanism,transition metals to activate methanol as alkylating agents often require more severe conditions.We hope to develop a transition metal catalyst that can accomplish N-methylation under milder conditions.The iridium complex[Cp*Ir(biim H₂)(H₂O)][OTf]₂ was synthesized and developed as a new-type of water-soluble metal–ligand bifunctional catalyst for the N-alkylation of poorly nucleophilic sulfonamides with alcohols in water.In the presence of catalyst(1 mol%)and Cs₂CO₃(0.1 equiv.),a series of desirable products was obtained in 74-91%yields under microwave irradiation.Mechanistic experiments revealed that the presence of NH units in the imidazole ligand was crucially important for the catalytic activity of the iridium complex.Notably,this research would facilitate the process of water-soluble metal-ligand bifunctional catalysis for the hydrogen autotransfer process.The third chapter of the dissertation successfully applied the metal-ligand bifunctional iridium catalyst to synthesize tertiary amines by automatic series transfer hydrogenation/methylation.A variety of tertiary amine products could be successfully obtained by reacting at0.3 equivalent of Cs₂CO₃ for 12 h at 130 ^oC.The catalytic system had mild reaction conditions,reacted in methanol,and was environmentally friendly.The only by-product produced is water,which has high atomic economy and conforms to the concept of green chemistry.