The Studies On Synthesizing Nitrogen Heterocycles Through Tandem Reaction Of O-arylation And [3,3]-rearrangement

Compounds containing N-o bond,such as O-aryl oxime ethers,O-alkenyl oxime ethers,nitrones and N-oxides,have been utilized extensively as important starting materials or intermediates to construct key building blocks in organic synthesis.These compounds could be served as key precursors to access benzoxazoles,benzofurans/dihydrobenzofurans,pyrrolidines,piperidines,indolizidine alkaloids,polysubstituted pyrroles,trisubstituted isoxazoles,aziridines,chiral primary amines,a-amino ketones and their derivatives,and so on.Up to now,they have been successfully applied in[1,3],[3,3]and[2,3]-rearrangements,cyclizations,cycloadditions,C-H activations,radical trapping reactions,and related transformations.In recent years,arylation of N-O bond combined with[3,3]-rearrangement has been demonstrated as a useful strategy in organic synthesis because of its fast construction of complex molecules,which played a very important role in the synthetic methodology and attracted much attention of chemists and pharmacologists.This thesis mainly focused on metal-free synthesizing heterocyclic compounds through tandem reaction of O-arylation and[3,3]-rearrangement.It could be divided into the following three parts:In the first part,we studied the method of metal-free O-arylation and[3,3]-rearrangement,which was used to prepare N-aryl benzo[1,2,3]triazin-4(1H)-one derivatives in good yields from N-hydroxy benzo[1,2,3]triazin-4(3H)-one and diaryliodonium salts in one-pot reaction.We have obtained 23 new compounds.The effects of different solvents,temperature and various bases were screened.The reaction was tolerated a variety of sensitive functional groups.A rational mechanism was proposed on the basis of the controlled experimental results.In the second part,we investigated the Chan-Evans-Lam coupling reaction of N-hydroxybenzotriazoles and alkenyl or aryl boronic acids to synthesize 1-vinyl/aryl benzotriazole 3-oxides.The effect of different solvents,temperature and catalyst were studied.This strategy features mild reaction conditions,good functional group tolerance,and compatible to modify complex bioactive compounds.DFT calculations revealed that the formation of the favored N-coupling product depended on the formation of the thermodynamically more stable N-C bond products in the Chan-Evans-Lam reaction.In the third part,on the basis of the first part work,we found that amidoximes reacted with readily available diaryliodonium salts under metal free mild conditions to form O-arylation products selectively instead of N-arylation products.The obtained arylation of amidoximes could undergo[3,3]-rearrangement and condensation under trifluoroacetic acid conditions to yield substituted benzoxazoles.The effect of different solvents,temperature and the species of additive were examined.The methodology was easily applied to synthesize a double benzoxazole,which was already used as N-ligand in transition metal catalysis.