Hypervalent Iodine(?) Reagents Mediated Formation Of Cyclic Compounds And Selective Halogenation

Hypervalent iodine(?)reagent is an active electrophile and goes through similar reaction patterns with transition metals.It is non-toxic,environmentally benign,and easy to be prepared.Hence,in recent years,hypervalent iodine(?)reagent is broadly used in all aspects of organic synthesis.In the first charpter of this dissertation,the use of hypervalent iodine compound in cycloaddition,oxidative cyclization and C-H bond activation was briefly reviewed.Based on the oxidizing properties of hypervalent iodine(?)reagent,we studied the in situ generation of 1,3-dipoles and their applications in one-pot reactions.First,we disclosed a PhIO/MgO protocol that can oxidize aromatic aldoximes to nitrile oxides that react in situ with acetonitrile or aromatic nitriles.Various substituted aromatic aldoximes can react with acetonitrile and the corresponding 1,2,4-oxazoles can be isolated in 68-95%yields.Using 8 equivalents of aromatic nitriles,the reaction with 4-chlorobenzaldehyde oxime went well and the desired products were obtained in 65-80%yields.Using readily available N-tosylhydrazones as starting martierals and HTIB as oxidant,we succeeded in producing a series of 1,4-dihydro-3,6-disubstituted-1,4-bis(p-toluenesulfonyl)-1,2,4,5-tetrazines.We postulated that the reaction produces nitrile imine in situ,and the dimerization of nitrile imine leads to the product.3,6-Disubstituted 1,2,4,5-tetrazines can be easily obtained by subsequent deprotection/aromatization of the dimer.PhIO was proved to be a powerful and efficient oxidant to oxidize N-unstubstituted hydraozones to diazo compounds.With the aid of nickel catalyst,diazo compounds react with alkenes at 80? to furnish cyclopropanes efficiently(5 min-4 h)in moderate to good yields(42-91%).The mild protocol is generally applicable to aryl alkenes with different electronic effect substituents,alphatic internal alkenes and hydrazones derived from diaryl ketone,aryl-alkyl ketone and aldehyde.As hypervalent iodine(?)compound mediated oxidative cyclization is well-developed to construct heterocycles,we designed to use N-benzyl amide oximes as substrates and aimed to form intramolecular C-O bond by oxidative cyclization.It was found that DIB/K2CO3/DMF protocol meets our anticipation.The corresponding 2,5-disubstituted 1,2,4-oxazoles can be synthesized in 71-95%yields,and the protocol tolerates electron-rich aromatic ring(furyl)and electron-donating substituents(MeO,Me2N).The strategy of generation of diazo compound in situ from N-unstubstituted hydraozones was utilized to study the donor/donor metal carbenoid participated sp3C-H insertion reaction.By using PhIO as oxidant,Ni(OH)2 as catalyst,(diphenylmethylene)hydrazine goes through intermolecular sp3C-H insertion reactions with cyclohexene and 1,3-cyclohexadiene with medium yields.Applying the same protocol to intramolecular sp3C-H insertion reaction and we managed to synthesis various 2,3-dihydrobenzofuran derivatives in 50-88%yields.The selective C-H chlorination/bromination of amide was also studied.PhIO/ZnCl2/TFE protocol was developed to mediate ortho-chlorination of N-aryl amide,the protocol can apply to N-substituted benzoyl aniline and tolerates halogen or strong electron-withdrawing groups on the aniline ring which overcomes the defects of Pd-catalyzed ortho-chlorination.The coordination of ZnCl2 with amide and the formation of nitrilium intermediate were postulated.Replacing ZnC12 with ZnBr2,the protocol enables para-bromination of N-(phenyl)substituented benzamide and ortho-bromination of N-(4-substituented phenyl)benzamide with up to 98%yield.The reaction system is mild,efficient and avoids using toxic and corrosion bromine.