Study On The Construction Of Carbonyl-containing Heterocycles And γ-amino Acids Using CO₂ As The C1 Synthon

With the development of human industrialization,fossil energy has been overconsumed,resulting in releasing a large amount of"greenhouse effect"gas carbon dioxide,which has coursed serious effect on the environment and the sustainable economic development.From the viewpoint of chemical synthesis,CO₂ could be used as a cheap,readily available,non-toxic and renewable source of C1 sourse.By using CO₂ as a building-block for the synthesis of diverse fine chemicals has gained much attention.However,only limited examples of chemical conversion reactions of CO₂ that can be industrialized at present stage,and the diversity of the corresponding products are rather limited.Therefore,further development of chemical fixation reactions of CO₂ under mild conditions is still necessary.Recently,much progress has been made in the fixation of CO₂ triggered by nitrogen-or carbon-centered nucleophiles.However,there are still some shortcomings should be overcome,such as the narrow range of substrate scope and the lack of the diversity of products generated.It is of great significance to further develop green methods for the synthesis of biologically active compounds,such as carboxylic acids and heterocycles by using CO₂ as the carboxylic or carbonyl source.This paper mainly studied the synthesis of benzoxazin-2-ones,oxazolidin-2,4-diones,γ-amino acids,γ-lactams and other compounds by multi-component reaction with CO₂ as C1biluding-block.The main research contents include the following three parts:（1）Investigation on multicomponent reaction of propargyl amides,CO₂ and halogenated hydrocarbonsOxazolidine-2,4-diones with tetra-substituted enyl moiety is a kind of important bioactive molecules with a variety of pharmacological activities.Herien,a series of oxazolidine-2,4-diketones and their derivatives were synthesized by the transition metal catalyzed three-component reaction of propargyl amides,CO₂ and halogenated hydrocarbon.The reaction mainly underwent the following sequences:oxidative addition of halogenated hydrocarbon to Pd⁰,carboxylation of amide group with CO₂,trans-oxygen-palladium of alkenyl moiety,reductive elimination,etc.The control experiments have shown that copper salt could inhibit the hydrogen-carbonization of the C-C triple bond.（2）Multi-component reaction of 2-（α-arylenyl）arylamines,alkyl bromides and CO₂A novel visible-light promoted palladium-catalyzed three-component reactions of 2-（α-arylenyl）arylamines,bromoalkanes and CO₂ have been developed,to afford a series of benzooxazin-2-ketones in high yields.The reaction has good substrate adaptability,for instance,primary-,secondary-and tertiary-alkyl bromides worked well in this reaction.Based on the corresponding control experiments,it was proposed that the reaction underwent a cascade carboxylation,free radical addition of alkenyl moiety,single electron oxidation,and intramolecular cyclization.（3）Study on carboxylation/cyclization of olefins,sodium glycinates and CO₂We further realized the visible-light promoted carboxylation/cyclization of olefins by sodium glycinates to access diverseγ-amino acidsγ-lactams in high yields,respectively.Particularly,sodium glycinates could be served as a bifunctional reagent,which could not only be used as the precursor of ammonia alkyl radicals,but also the carboxylic source.The relative control experiments showed that the reaction was triggered by the reductive quenching of the photosensitizer by sodium glycinates.In addition,isotopic labeling experiments show that carboanion intermediates are formed during the reaction.