Visible-Light-Promoted Synthesis Of N-Containing Heterocycles

The energy of UV light is very high and harmful to human.Furthermore,organic reactions promoted by UV light often need special and expensive experimental facility(such as high pressure mercury lamp or xenon lamp)and reaction scale usually depends on the size of reaction containers,which limits the applications of UV light in organic synthesis.Sunlight as an inexhaustible,non-polluting energy has attracted more and more attention of chemists.Visible light,as the highest proportion of sunlight,almost comes to 46%.Using visible light instead of ultraviolet to catalyse organic reactions and developing green and sustainable organic photochemistry reactions,is still an important task for organic chemists.This paper will focus on two novel routes to generate radicals:visible light photoredox catalysis and halogen-bond catalysis.This paper is divided into five parts,as follows:1.Visible-light-promoted synthesis of 6-mono-and difluoromethylated phenanthridine derivatives.In this job,we chose ethyl bromofluoroacetate(EBFA)and ethyl bromodifluoroacetate(EBDFA)as fluorine source.A series of 6-alkylated phenanthridine derivatives were obtained in good to excellent yields at room temperature.Followed by decarboxylation,the desired 6-mono-and difluoromethylated phenanthridine derivatives could be synthesised in satisfactory yields.Furthermore,we also developed the one-pot procedure,which made this method more practical.2.Visible-light-promoted synthesis of quinoline and quinoxaline derivatives.In this part,we chose fac-Ir(ppy)3 as photocatalyst,a number of fused quinoline and quinoxaline derivatives were prepared by domino somophilic triple bond insertions via visible light irradiation.The skeletons of quinoline and quinoxaline were very important blocks for natural products and drug molecules.Furthermore,we avoided using ultraviolet irradiation and any toxic reagents.3.Visible-light-promoted synthesis of 6-(fluoro)alkylated phenanthridines.In this part,we developed a novel method for iminyl radical formation.We chose alkyl bromides and Umemoto's reagent as the precursors of alkyl and trifluoromethyl radicals,which added onto vinyl azides leading to iminyl radicals formation,followed by intramolecular HAS,oxidation and deprotonation,we could obtain a number of 6-(fluoro)alkylated phenanthridine derivatives with high yields and broad substrate scope.4.Halogen-bond-promoted synthesis of 2-fluoroalkylated quinoxalines.In this work,we developed a halogen-bond-promoted synthesis of 2-fluoroalkylated quinoxaline derivatives via double radical isocyanide insertion under visible light irradiation.It was found that fluoroalkyl radicals could be produced by a visible-light-promoted SET process when we chose perfluoroalkyl halides and organic bases as halogen bond partners.Furthermore,we also did a series of mechanism experiments and calculations to investigate the existence of a halogen bond complex.5.Halogen-bond-promoted atom transfer radical addition of alkynes.Atom transfer radical addition(ATRA)usually requires harsh conditions,such as stoichiometric amounts of initiators and high reaction temperature.In this work,we developed a halogen-bond-promoted generatation of fluoroalkyl radicals by visible light irradiation.Subsequently fluoroalkyl radicals added to terminal alkynes to afford the corresponding iodoperfluoroalkylated alkenes with high yields and broad substrate scope at room temperature.The resulting perfluoroalkylated alkenyl iodides could be further functionalized by cross-coupling reactions.