The Research Of Visible-light Photo-catalyzed External Oxidant-free Oxidative Coupling Reactions

The concept of "green chemistry" and "sustainable chemistry" leads the drastic changes in the field of organic synthesis.The development of new reactions to improve the efficiency of resources,energy efficiency,product selectivity and environmental safety in organic synthesis has become an important research field.Oxidative cross-coupling is one of the frontiers in modern organic synthesis research.Compared with the traditional cross coupling reaction,the nucleophiles can be used as the starting materials of the reaction in oxidative coupling,which can avoide pre-functionalization steps of substrates.Recentlly,the development of photoredox catalyzed organic synthesis has injected new blood into the development of oxidative coupling.Especially,cross dehydrogenation coupling of hydrocarbons has become an ideal synthetic method.In the oxidative coupling reaction,however,the use of stoichiometric oxidants would bring the unwanted chemical waste.The ideal oxidative coupling would be the directly oxidative cross-coupling reaction under external oxidant-free conditions.Therefore,the development of a catalytic system to achieve this goal is still challenging but significant.In this doctoral dissertation,the history of the development of oxidative coupling and the application of photocatalytic dehydrogenation process in synthesis are introduced.Then the development of photoredox catalyzed oxidative coupling is reviewed.With respect to green chemistry concept,the oxidative cross-coupling reactions in the absence of additional oxidants were developed by the combination of photoredox catalysis and hydrogen reducing catalysis.Meanwhile,the mechanism of the reaction has been explored by kinetic research,which revealed the inherent law of these reactions.The main results of this study are as follows:1.Based on the dual catalytic system including photoredox catalyst and cobaloxime catalyst,the intramolecular oxidation cyclization reaction of benzoylaniline derivatives under the condition of no external oxidant has been developed.This reaction can achieve the synthesis of benzothiazole derivatives with H2 evolution as the only byproduct.When the TBAOH was used as the base,both of 2-aryl and 2-alkyl benzothiazole can be synthesized by this method,which can effectively avoided the formation of the amides by-product.The mechanistic studies showed that hydrogen is derived from substrates and the protonation of cobaloxime might be a rate-determining step of the reaction.2.Using eosin Y as the photosensitizer,combined with a cobaloxime catalyst,the intermolecular formation of carbon-sulfur of a-alkyl styrene with sulfonic acid derivatives can be achieved.The allylic sulfonation of a-alkyl styrene is the major product of this reation,which accompany with the generation of H2.As a radical acceptor,olefins can effectively trap the photogenerated sulfonyl radicals.3.Olefins can not only be used as a radical acceptor,but also can be regarded as the electron donor under strong oxidative conditions.Based on the free radical cation intermediates generated from the photocatalyzed single-electron-oxidation of olefin,we have realized the anti-Markovnikov Wacker-type oxygenation and hydration reactions of olefin.The oxygenation process of styrene derivatives can be achieved by a dual catalytic system including acridine photosensitizer and cobaloxime catalyst.H2 is the only by-product of the reaction.When the hydrogen atom transfer catalyst,phenyl disulfide,was used instead of cobaloxime,the anti-Markovnikov hydration of olefin can be achieved.These transformations can avoide the use of oxidant and noble metal catalyst,which greatly improved the atomic economy and reduced the cost of reaction.4.The sequenced Diels-Alder/oxidation reaction represents a powerful route for the construction of six membered aromatic compounds in organic synthesis.A dual catalytic system including an acridine photosensitizer and cobaloxime catalyst would lead the dehydrogenative[4+2]cyclization between styrene and electron-rich dienophiles.Many aromatic compounds can be synthesized without using stiochiometric chemical oxidants.The gram synthesis can be achieved by using solar as the light source.With respect to atom and step-economy ideals,this dual catalytic system enables the formation of high-value molecules from feedstock chemicals.5.It was found that the interaction of elemental sulfur and strong base would produce a trisulfur radical anion.And the 1,3-butadiyne can be used to capture the free radical species.Various 2,5-disubstituted thiophenes can be synthesized.The EPR studies indicate that trisulfur radical anion might be the key intermediate of the reaction.