Studies On Cascade Reactions Of Aziridines

Development of new reactions is one of the most attractive areas in organic chemistry.In this thesis,we have studied a series of new types of cascade reactions of aziridines.The details are summarized below:(1) A cascade reaction of aziridines and propargylic alcohols to functionalized indenes has been developed.A plausible mechanism for this approach has been proposed as follows:In the presence of LA,the in situ ring-opening of aziridine generates an azomethine ylide,while propynol is converted to the cationic intermediate via a Meyer-Schuster rearrangement.Then,azomethine ylide reacts with cationic intermediate through a[3+2]cycloaddition to form a five-membered ring carbocation.Deprotonation along with the ring opening of five-membered ring carbocation leads to the formation of imine,which is sequentially transferred into the final indene product via an intramolecular Friedel-Crafts reaction promoted by LA. Since the substrates are readily available and the products can be converted to polycyclic indenes,indenimines and indenones,this approach may prove to be useful for the synthesis of biologically active indene derivatives and related carbocycles.(2) A cascade reaction of aziridines and ethyl diazoacetate to 1,3-diazabicyclo[3.1.0]hex-3-ene system has been developed.A plausible mechanism for this approach has been proposed as follows:The diazo acetate reacts with CuI to give the copper-stabilized carbene complex,next,carbene complex reacts with the aziridine by N-H bond insertion to give the N-alkylaziridine,which decomposed to chalcone and ethyl-2-iminoacetate.Aziridine reacts with ethyl-2-iminoacetate by nucleophilic addition to form a diamine,then it undergoes cyclization to the 1,3-diazabicyclo[3.1.0]hex-3-ene system.This mild and efficient approach provides 9 compounds.(3) A cascade reaction of aziridine,dialkyl azodicarboxylates and aldehydes to hydrazinecarboxylates has been developed.A plausible mechanism for this approach has been proposed as follows:The phosphine reacts with the azoester to form the Huisgen zwitterion,then the zwitterion reacts with aldehyde and aziridine sequentially to form the hydrazinecarboxylates.