Study On Base-Promoted Reactions Of N-aryloxyalamine And Alkynylated Hypervalent Iodines

Highly functionalized oxazole is very important heterocyclic motif in biologically active natural products,pharmaceuticals and materials.Benzofurans have pharmaceutical and biological activities including anti-fungal,anti-bacterial,anti-inflammatory and anti-cancer and anti-proliferation.The synthetic methodology by metal catalysis provides great convenience to synthesize specific target molecules,but it also causes some pollutions to the environment.Therefore,the development of efficient metal-free reactions is in line with the current trend of green chemistry.N-Phenoxyamides have been reported in transition metal-catalyzed C-H activation for the alkynylation,olefination and heteroarylation,however,the metal-free catalytic annulation which shows new distinct reactivity of N-phenoxyamides hasn’t been disclosed.Ethynylbenziodoxolones（EBXs）as a source of electrophilic acetylene equivalents,could efficiently react with different substrates to afford alkynylation products.Although EBXs have gained a lot of success for the C-H bond functionalization,there are few studies on transformations other than alkynylation of EBXs.On the basis of our research group devoted to the design and synthesis of heterocyclic compounds,a synthetic protocol for the construction of 2-（oxazol-5-yl）phenol derivatives promoted by K₂CO₃ from N-phenoxyamides and alkynylbenziodoxolones at room temperature and DCE as solvent has been developed.Thirty-one polysubstituted oxazole derivatives were synthesized and the reaction mechanism was investigated by several control experiments,such as,radical capture experiment,crossover experiment and kinetic isotope effect experiment.The metal-free conditions,broad substrate scope and simple execution make this novel protocol very attractive.In the course of exploring the substrate tolerance of oxazole derivatives,TIPS-EBX shows different reactivity.A new method for the preparation of benzofuran derivatives using N-phenoxyamides and TIPS-EBX as materials was established by adding TBAF.Thirty-three substituted benzofuran derivatives were successfully synthesized by this strategy.The structures of all the target compounds were confirmed by ¹H NMR,¹³C NMR and HRMS.The structures of target compounds have been confirmed by the X-ray single crystal diffraction analysis of compounds 3aa、3a and 4a.