Visible-Light-Promoted[2+2]?[3+2]Cycloadditions For The Construction Of Nitrogen-Containing Compounds

[2+2]and[3+2]cycloadditions are convenient strategies to access nitrogen-containing carbolic cyclobutanes/cyclopentanes,which are important motifs of medicine and nature products.UV light promoted[2+2]cycloadditions are commonly used for the synthesis of nitrogen-containing carbolic cyclobutanes and usually restricted in intramolecular reactions.The highly regio-and diastereoselective intermolecular[2+2]cycloadditions is still a challenge.[3+2]cycloadditions of 1,3-dipolar precursors with olefins/enamines mainly serve as direct strategies for the preparation of nitrogen-containing carbolic cyclopentanes.Customarily,donor-acceptor nitrogen-containing cyclopropanes or enamines are employed as nitrogen sources in[3+2]cycloadditions.Therefore,the development of new strategies for the efficient construction of nitrogen-containing cyclobutanes/cyclopentanes is still highly desirable.Visible-light-promoted organic transformations have many advantages,such as green,operationally simple and high efficiency.Visible-light-promoted[2+2]/[3+2]cycloadditions could also be used to access nitrogen-containing cyclobutanes/cyclopentanes.In the dissertation,the syntheses of nitrogen-containing cyclobutanes/cyclopentaneswe are described via visible-light photocatalysis,The dissertation could be divided into three sections,as follows:1.The highly regio-and diastereoselective construction of strained polysubstituted 2-azabicyclo[4.2.0]octanes with three all-carbon quaternary centers has been achieved through visible-light promoted[2+2]cycloadditions of bioactive 1,4-dihydropyridines with olefins.This strategy using Ir?ppy?3 as a photosensitizer and MeCN as a solvent is operationally simple,atom-economical with good functional group tolerance and the products can be easily converted to various structurally unique derivatives.The primary mechanistic studies demonstrated that the reaction proceeded through an energy transfer pathway.2.The visible-light promoted catalyst-free[2+2]cycloaddition of trans-?-nitrostyrenes with olfins has been accomplished using a 8 W blue LED as light source and toluene as a solvent.The reactions between various trans-?-nitrostyrenes and olfins can be completed in 48-96 hours,yielding nitro-containing cyclobutanes.This protocol is operationally simple with broad substrates scope using relatively simple and readily available starting materials.3.The first nitro-initiated redox-neutral[3+2]cycloaddition of nitrocyclopropanes with styrenes using Ru?bpy?₃?PF₆?₂ or Ir?ppy?₂?dtbbpy??PF₆?as a photocatalyst and Et3N as a reductant has been reported.The protocol is operationally simple with broad substrates scope.The mechanistic studies demonstrated that the reaction was initiated by single-electron-reduction.Additionally,high diastereoselectivities were observed between two quaternary carbon centers on the ring and validated by DFT calculations.In summary,nitrogen-containing cyclobutane/cyclopentane core skeletons have been constructed efficiently under mild conditions.The[2+2]cycloadditions of bioactive 1,4-dihydropyridines with olefins,the catalyst-free[2+2]cycloaddition of trans-?-nitrostyrenes with olfins and the nitro-initiated redox-neutral[3+2]cycloadditions of nitrocyclopropanes with styrenes have been efficiently achieved for the synthesis of nitrogen-containing cyclobutanes/cyclopentanes in the presence of visible-light.Further extended to other radical reactions and asymmetric transformations of nitrogen-containing carbolic compounds will be next stage of work.