SalenCo Complex Catalyzed Asymmetric Electrocarboxylation To Prepare Chiral Carboxylic Acids

Carbon dioxide is an important part of the global carbon cycle,and it has extremely high stability with highest oxidation state of carbon.At the same time,carbon dioxide is a safe and easily available renewable resource.The use of carbon dioxide to synthesize high value-added fine chemical products is a research hotspot in green chemistry.Due to the special structure of the carbon dioxide,the synthesis of carboxylic acid compounds using carbon dioxide has a long history.The reaction of carbon dioxide often requires harsh conditions,and studies on the synthesis of chiral carboxylic acid compounds using carbon dioxide are rarely reported.Chiral carboxylic acid compounds are widely present in medicines,natural products,and biologically active molecules.Therefore,it is highly desirabale to develop a method for synthesizing chiral carboxylic acid compounds with carbon dioxide.Electrochemical organic synthesis is a sustainable redox reaction by applying voltage or current to the reaction and using electrons as a reagent to drive the chemical reaction.Electrochemistry only needs to control the electrode potential to obtain highly active reaction intermediates,with mild and efficient reaction conditions.The asymmetric catalytic reaction of carbon dioxide catalyzed by chiral metal complexes is an important way to obtain chiral carboxylic acid compounds.However,stoichiometric reductive reagents are often required.Combining organic electrochemical synthesis with asymmetric catalysis can avoid the use of reductive reagents and is the frontier field of electrochemical organic synthesis.In this paper,we have developed an electrochemically driven metal complex catalyzed asymmetric carboxylation to synthesize chiral 2-arylpropionic acid compounds.In this thesis,the electrochemical behavior of several chiral Salen metal complexes was studied by electrochemical techniques.When Ag/AgI was used as the reference electrode,chiral biSalenCo complexes showed good asymmetric catalytic potential.Then the effect of carbon dioxide and the reaction substrate 1-chloro-1-benzeneethane on the electrochemical behavior of（S,S）-SalenCo（II）was studied.Through the analysis of reaction intermediates and reaction mechanism,it was observed that the formation of chiral metal complex[PhCH（CH₃）SalenCo（II）]^-is the key to the realization of asymmetric carboxylation.We carried out asymmetric carboxylation of 1-chloro-1-phenylethane under constant current and constant voltage conditions,and investigated the chiral catalyst,cathode material,reaction temperature,electrolytic potential and current density on the reaction yield.Under optimal conditions using chiral biSalenCo（II）catalyst,the enantiomeric excess of 2-phenylpropionic acid can reach 77%.At the same time,we further studied the electrochemical behavior and the asymmetric electrocarboxy-lation reaction of the electron-deficient substrate.Carbonyl sulfide is a hazardous sulfur-containing gas.We also developed a base-promoted cyclization reaction of phenylyne hydrazone with carbonyl sulfur,to synthesize thiadiazine-2-one compounds.Through the investigation of the reaction conditions such as base,amount of base and solvent,the obtained the optimal reaction conditions are:0.1equivalent of Cs₂CO₃ as the base,CH₃CN as the solvent and reacted at 60 ^oC for 12 hours.Under optimal conditions,the yield of thiadiazin-2-one can reach up to 77%.The yield of the electron-rich substrate was significantly higher than that of the electron-deficient substrate,and a variety of thiadiazine-2-one compounds were synthesized.