Study On The Construction Of Carbon Heterobonds Under Photochemical Conditions

Carbon heterobonds are common structures in natural products.Compounds containing carbon heterobonds(including C-O,C-N bonds,etc.)have a wide range of applications in the fields of medicine,agriculture,daily necessities,and materials.In recent years,metal-catalyzed photoredox construction of carbon heterobonds has developed rapidly.Photocatalytic excitation of various carbon-centered free radicals,combined with the unparalleled bonding ability of transition metals,enables the construction of a large number of carbon-hetero containing functional groups(aldehydes,ketones,esters,carboxylic acids,amines,oximes,nitriles).However,metal-catalyzed photoredox reactions still have shortcomings that cannot be ignored: expensive metal catalysts(iridium,ruthenium,etc.),or stoichiometric acid-base additives,or harsh reaction conditions.Therefore,there is an urgent need to continue to develop more green,efficient and inexpensive photocatalysts to realize the photocatalytic C-heterobond construction with mild reaction process.In this thesis,a cheap and readily available TBATB(tetrabutylammonium tribromide)was used as a photocatalyst to study the construction of carbon-hetero bonds.(1)Photocatalysis has been widely used in the construction of C-O bonds based on the advantages of green environmental protection and mild conditions for photoredox reactions.We used photocatalytic excitation of carbon radicals to generate peroxides,and further developed and studied photocatalytic synthesis of ketones.We use ethyl aromatic hydrocarbon as raw material,cheap and easily available tetrabutylammonium tribromide as catalyst,molecular oxygen in the air as oxidant,and irradiated the mixture with white light at room temperature for 48 hours.The model reaction yield reached 85%.The reaction system was suitable for various benzene ring-substituted ethylbenzenes,and 29 kinds of aromatic ketones and heteroaromatic ketones were obtained in good yields.We also performed a scale-up reaction to explore the utility of this reaction.We then attempted methyl oxidation to give the aldehyde as the product.The final mechanistic study revealed that the reaction go through a free radical mechanism involving a peroxide intermediate.(2)C-H activation to construct C-N bonds has developed rapidly.Based on the oxidation reaction of benzylic carbon-hydrogen bonds in our study,we studied how to functionalize C-H bonds to directly obtain cyanide products.We used various modified toluene as raw material,molecular oxygen as oxidant,hydroxylamine hydrochloride as nitrogen source,and reacted in acetonitrile solvent under the irradiation of white LED lamp for 48 hours to obtain C-N bond-containing products.By controlling the conditions of temperature and additives,we could selectively obtain various aryl oximes and aryl nitrile products in yields ranging from 30% to 85%.