A New Hypervalent Iodine (Ⅲ/Ⅴ) Oxidant And Its Application To The Synthesis Of 2H-Azirines

In the past several decades hypervalent iodine chemistry has witnessed prosperous development in organic synthesis.On one hand,organic chemists are making use of the existing hypervalent iodine oxidants to discover new organic reactions.On the other hand,many endeavors have been devoted to the development of novel hypervalent iodine oxidants,seeking for new versatile applications in important synthetic transformations.In this regard,designing novel hypervalent iodine compounds and discovering their new application continues to be an important research topic of hypervalent iodine chemistry.The existing hypervalent iodine reagents can be generally classified into iodine(Ⅲ)and iodine(Ⅴ)based on the valance of the iodine atom.It is evident that all these hypervalent iodine compounds whether it bears one single iodine atom center or the multinuclear iodine centers,all have a sole valence number of either I(Ⅲ)or I(Ⅴ)present in its chemical structure.To the best of our knowledge there is no report on a hypervalent iodine compound that bears both I(Ⅲ)and I(Ⅴ)moieties in its chemical structure.Herein,we reported such an unprecedented hypervalent iodine compound bearing concurrently I(Ⅲ)and I(Ⅴ)moieties and its preliminary application in the synthesis of 2-unsubstitued 2H-azirines,which could not be efficiently achieved by the existing known hypervalent iodine reagents.When o-nitroiodobenzene reacted with m CPBA in acetic acid at 60 ~oC for 3 h,a hypervalent iodine(Ⅲ/Ⅴ)186 was formed as an orange solid(the structure was undoubtedly confirmed by X-ray analysis).A careful literature survey indicated that this could represent the first hypervalent iodine compound containing both I(Ⅲ)and I(Ⅴ)moieties in its chemical structure.The X-ray data revealed that four crystallographically independent molecules are present in one crystal unit cell.Molecule 186 assembles in a unique“scissor”manner as a result of intermolecular I(2)···O(5)and I(1)···O(4)interactions.The crystal structure of 186 is unique among the known hypervalent iodine structures that have been characterized to date with a pentavalent I(2)atom and a trivalent I(1)atom coexisting in one molecule via connection of O(3)atom.In addition,the DFT calculations were performed for molecular electrostatic potential surface.Electro-positive regions(surface maxima)around I(Ⅲ)or I(Ⅴ)atoms displayed electrostatic interaction with oxygen atoms of nitro groups.The calculation results indicated that nitro groups played an essential role in molecule 186.We were interested to investigate the applicability of this newly discovered hypervalent iodine(Ⅲ/Ⅴ)oxidant.Fortunately,it was found in this work that this newly discovered hypervalent iodine(Ⅲ/Ⅴ)is a key in the azirination synthesis of2H-Azirines demonstrating the unique property of this hypervalent iodine oxidant.With the optimized conditions in hand,substrate scope study was carried out by using this newly discovered hypervalent iodine(Ⅲ/Ⅴ)reagent on a series ofα-substituted enamines.It was observed that a variety of substituents on the phenyl ring could be well tolerated during the reaction.Regarding to the substituent effect of R group substrates bearing electron-withdrawing groups or electron-donating groups at the para-position of the phenyl ring both gave the corresponding products in good yields,with the substrates bearing electron-withdrawing groups affording better outcome.Lower yield was obtained for substrates containing substituents at meta-position of the phenyl ring.While for the substrate bearing an ortho-substituent methyl group on the phenyl ring the desired 2H-azirine product was only afforded in a much lower yield.This work reports the existenceof a new hypervalent iodine oxidant containing both I(Ⅲ)and I(Ⅴ)moieties in its chemical structure for the first time.Computational experiments were carried out and showed that the nitro group at the ortho phenyl position is crucial in stabilizing this exclusive structure.This novel hypervalent iodine(Ⅲ/Ⅴ)oxidant can be applied to the synthesis of 2-unsubstitued2H-azirines,which cannot be successfully achieved by other traditional hypervalent iodine reagents.Further application of this hypervalent iodine(Ⅲ/Ⅴ)oxidant is currently under study in our lab.