Study On The Application Of Organoboron Catalysts In Photo-oxidation Reactions And Cycloaddition Reactions

After recent decades of research and development,non-metallic catalysts and non-metallic catalytic systems have developed rapidly and are widely used in organic synthesis and chemical production.However,there is still a big gap between non-metallic catalysts and traditional metal organocatalysts in terms of reaction activity,product selectivity and adaptability.Therefore,the development of highly active non-metallic catalytic systems has also become a hot research topic nowadays.Organoboron compounds,which have empty p orbitals and thus exhibit metal-like Lewis acidity,are expected to complement the conventional metal organocatalytic systems,especially for their efficient electrophilic activation of nucleophilic reagents.On the other hand,some organoboron compounds are also very promising materials for optoelectronic functions.The common ones are tetra-coordinated organoboron compounds,which are represented by the boron fluoride coordination dipyrrometacene(BODIPY)class of compounds,which are widely used in photodynamic therapy,chemical and biological sensing,organic light-emitting diodes,etc.However,compared with applications in other fields,tetra-ligand boron compounds are less used in visible light-catalyzed organic reactions,and the only applications are with BODIPY-like compounds as photosensitizers.Therefore,it is necessary to develop a novel organoboron-based catalyst for photocatalytic organic transformations.In summary,this thesis is devoted to the study of organoboron catalysts in two major directions: photo-oxidation and cycloaddition reactions.The main research of this thesis is divided into four main parts as follows:(1)This chapter works on organoboron-catalyzed intramolecular cycloaddition reactions of unactivated alkenyl cyclopropanes.We have discovered a novel method to induce intramolecular ring-opening of cyclopropane,by which a series of novel cyclopentenes are obtained.The method is metal-free,easy to operate,and yields can reach up to 96%.Finally,the mechanism was explored and the reaction was concluded to be a free radical involved reaction.(2)The work in this chapter is a study of organoboron-catalyzed hydroxylation of organoboronic acids under visible light-mediated conditions.The method uses a novel B,B-bisaryl tetra-ligand boron compound as a photocatalyst and various types of organoboronic acids as starting materials to obtain phenolic products with various functional groups in excellent yields up to 99% under metal-free conditions using air as an oxygen source under ambient visible light conditions.Subsequently,expanded volume experiments were performed to explore the practicality of the reaction.Finally,an exploratory study of the mechanism was carried out and it was concluded that the reaction is one involving superoxide radicals.(3)The work in this chapter is a study of visible-light-mediated organoboron-catalyzed oxidative dehydroaromatization reactions of N-heterocyclic compounds.The method uses a novel B,B-bisaryl tetra-ligand boron compound as a photocatalyst for the dehydroaromatization of N-heterocyclic compounds in excellent yields up to 97% at room temperature under visible light conditions using oxygen as the oxygen source without metals or additives.Subsequently,we achieved the ring closure and dehydroaromatization of N-heterocyclic compounds by a one-pot method using o-amino compounds and aldehydes as starting materials under the above standard conditions.Finally,the mechanism was explored and it was concluded that the reaction is a reaction involving superoxide radicals.(4)The work in this chapter is a study of visible-light-mediated organoboron-catalyzed oxidation reactions for C-N,C-S,and C-Se bond breaking.We developed a new method for visible light-induced selective oxidative breakage of C-N,C-S,and C-Se bonds.The method uses a novel B,B-bisaryl tetra-ligand boron compound as a photocatalyst and molecular oxygen and water as oxidants.By this method,a series of carbonyl compounds can be obtained in good yields up to 90% under mild metal-free conditions.Finally,an exploratory study of the mechanism was carried out and it was concluded that the reaction is one involving superoxide radicals.