Studies On Intramolecular Cyclization Of Diazonium Compounds Promoted By Visible Light

Diazo compounds are the main precursors of carbenes,and are widely used in carbene based transformations,such as cyclopropanization,C-H and X-H insertion,Wolff rearrangement,and conversion through Yellowstone intermediates.They play a very important role in organic synthesis.The reported methods of pyrolysis,UV photolysis,and metal catalyzed synthesis of carbene have limited their development due to their harsh reaction conditions,low selectivity,and metal residues.In recent years,the carbene transfer reaction involving diazo promoted by visible light has become one of the hot spots in organic synthesis chemistry research due to its advantages of simple operation,no need for metal catalysts,and in line with the concept of green chemistry.In this master’s thesis,we first studied the intramolecular cyclization of fluorene promoted by visible light under mild conditions.The intermolecular reactions previously reported in the literature have achieved good reaction results,but there are few reports on intramolecular reactions.So it is of great significance to study this.In addition,this study has also applied this method to other diazo substrates,effectively synthesizing various aromatic structures such as cycloheptane,benzoxazine,and benzazetidine compounds.The specific research contents are as follows.In the second chapter,diaryldiazoacetate was used as a model compound.It was found that the substrate could efficiently promote the intramolecular cyclization of fluorene under the promotion of visible light at room temperature.Then under the optimized reaction conditions,22 cyclization products were obtained in 90-99%yield.The UV-visible absorption spectra and theoretical calculations show that the n-π* transition of diazo groups is the key to their specific excitation by blue light.The mechanism of C-H insertion was determined by kinetic isotope effect study and density functional theory calculation.In addition,an unsaturated aldehyde of indene was obtained for a special ring opening reaction using 2-position furan as the substrate,and a reasonable explanation for the reaction mechanism was given through theoretical calculations.In the third chapter,we further extend the visible light promoted intramolecular cyclization reaction to Buchner reaction.By using only blue light as the driving force of the reaction,under the optimized reaction conditions,through the intramolecular Buchner reaction,a series of cycloheptane derivatives were efficiently obtained.The substrate of the reaction has good applicability,with diazo on the p-benzene ring α All substituents have good derivability.Compared with the traditional metal catalyzed Buchner reaction,the reaction conditions are mild and the operation is simple.In addition,the reaction mechanism was reasonably explained by theoretical calculation.In the fourth Chapter,we attempt to further synthesize benzoxazine heterocyclic compounds using this method,and preliminary experiments have obtained two mixtures of benzoxazine and benzazetidine compounds.This indicates that the active intermediate of the reaction is not selective at the reaction site.To solve this problem,we screened the reaction conditions and found that different solvents have a significant impact on the reaction.When dioxane is used as a solvent,a single product dominated by benzoxazine is obtained,while equal amounts of benzoxazine and benzazetidine compounds are obtained in acetonitrile.Subsequently,the corresponding benzoxazine and benzazetidine products were obtained by controlling the reaction conditions with moderate to high yield.