Synthesis Of Chiral Nitrogen-Containing Heterocycles And Fluorinated Carboxylic Acids Using Carbon Dioxide

Carbon dioxide(CO₂)is not only the most abundant greenhouse gas,but also an inexpensive and renewable carbon resource.It is of great significance to utilize CO₂ in chemical conversion to synthesize value-added compounds,which represents an important task of green carbon science.However,the thermodynamic stability and kinetic inertness of CO₂ make its chemical conversion to be a challenging issue.This dissertation focuses on the development of new synthetic methods to obtain chiral nitrogen-containing heterocycles and fluorinated carboxylic acids with CO₂ as C1synthon.Accordingly,the silver-catalyzed carboxylative cyclization of(homo)propargyl amines,as well as the direct electrochemical defluorinative carboxylation of Csp³-F bond were explored,which included following research work:1)By employing a dual catalysis of DPG/Ag OBz,a carboxylative cyclization of N-aryl propargylamines and CO₂ for the synthesis of N-aryl 2-oxazolidinones was developed,whilst the side alkyne hydroarylation process was suppressed.With this aid,the first tandem asymmetric A³(aldehyde,amine and alkyne)coupling-carboxylative cyclization sequence was achieved to synthesize optically active N-aryl 2-oxazolidinones from simple starting materials aldehyde,amine and alkyne with CO₂.The copper species and ligand that used in the upstream A³ reaction were found to facilitate the downstream Ag-catalyzed carboxylative cyclization.This represented the first sustainable tandem reaction that internally recycled the metal catalyst and ligand from the previous step were reused as the additives to accelerate the subsequent step.2)The above developed dual catalysis of DPG/Ag was further successfully applied to develop an unprecedented highly efficient carboxylative cyclization of homopropargyl amines with CO₂ facilitated by the combination of DPG and Ag Sb F₆,allowing the smooth synthesis of structurally diverse chiral and achiral 1,3-oxazinan-2-ones under ambient temperature and pressure.A mechanistic study revealed that DPG was critical to the reaction,which not only increased the effective concentration of CO₂in solution,but also improved the catalytic activity of Ag Sb F₆,and stabilized the reaction intermediates.As demonstrated by X-ray analysis,the three N–H bonds of DPG was the key to the stabilization of[DPGH][HCO₃].3)An efficient electrochemical?-carboxylation of?-CF₃ alkenes with CO₂ was developed to provide an access to vinylacetic acids bearing a gem-difluoroalkene moiety,which constituted a method of using an electrochemical process to secure regioselectivity that differed from that of the metal-catalyzed process.This approach was realized under mild conditions with a broad range of functional groups,avoiding the usage of sacrificial anode,and represented a rare electrochemical defluorinative carboxylation using H2O as promotor.Preliminary mechanistic studies suggested that an ECEC(single-electron reduction,reaction with CO₂,single-electron reduction,loss of fluoride)process should be involved at the cathode,and the oxidation of DMF or H₂O occurred at the anode.