Transition-metal-free Oxidative Coupling Reactions

The efficient construction of C-C and C-X(hetero atom)bonds is of great significance in the field of organic synthesis.The transition-metal-free oxidative coupling reaction is a kind of sustainable synthetic method capable of efficiently constructing C-C and C-X bonds.In recent years,transition-metal-free oxidative coupling reaction has attracted a lot of attention and been vigorously development in organic chemistry.Combined with our previous research,this thesis focuses on the synthesis of?-aminophosphonates,oxazoles,and allylamines under transition-metal-free oxidative conditions.The main contents and results are listed as following:Part 1:DDQ promoted C-P bond coupling for synthesis of?-aminophosphonatesThis procedure involved C-P bond formation under transition-metal-free conditions.We have developed a novel synthetic method of?-aminophosphonates using DDQ as oxidant.The reaction is facile,efficient,atomic economy,and compatible,in which the yield is up to 99%.Mechanistic studies indicated that an imine intermediate is formed and radical process is existed in the transformation.The reaction could be scaled up to grams with good yield,illustrating important potential industrial application.Part 2:DDQ promoted C-C bond coupling for synthesis of allylamineA transition metal-free pathway for constructing C-C bond under the mild oxidation system was developed.In this transformation,the oxidation system comprised of DDQ,and allyltributyltin as the allyl regent.The allylation reaction of the?-position of sp~3 C-H bond of the secondary amine was achieved and the corresponding allylamine product was obtained.A reasonable mechanism was proposed,in which a vital imine intermediate formed through DDQ oxidation of N-benzyl aniline.Part 3:hypervalent iodine regent promoted intramolecular coupling/rearrangement/cyclization for synthesis of oxazolesAn oxidation method was proposed to prepare oxazoles from the corresponding enol amines using hypervalent as the oxidant.The polysubstituted oxazole compounds were produced by oxidative coupling,rearrangement and cyclization of the enol amine substrates.Radical process of the reaction was confirmed by radical inhibition experiments.Control experiments uncovered a process that the reaction may firstly form isoxazole intermediate and then transform into oxazole.Sunlight illumination can also facilitate this transformation.Oxazole structure was confirmed by X-ray single crystal diffraction.