The Chemoselective Ring-opening Metathesis Polymerization Of Sspirocyclopropene Derivatives

Cyclopropenes is the smallest unsaturated ring compound in nature.It was very reactive due to its high strain energy.Ring-opening metathesis polymerization(ROMP)is an important class of olefin metathesis reaction,which has been widely used in the construction of organic polymer compounds and the development of new polymer materials.The ring-opening metathesis polymerization of cyclopropene has been widely reported.The research showed that the substituents on the saturated carbon of cyclopropane and the catalyst have important effects on the chemoselectivity and stereoselectivity of polymerization.However,the mechanism leads to the selectivity differentiation is not clear.It has been reported that Grubbs-Ⅰ catalyzed spirocyclopropene containing an N-aryl substituted azetidine gives E-linear polymers,while the E-cyclic polymers was obtained under Grubbs-Ⅱ catalyzed reaction condition.Based on previous research,the selectivity of ROMP reaction of spiropropene derivatives was further studied in this thesis.The aim is to explore the effect of substituent groups and catalysts on the selectivity of ROMP reaction and the reaction mechanism.The research content is as follows:In this thesis,piperidine-appended spirocyclopropenes were designed and synthesized and their ROMP reactions were studied under different catalytic conditions.Using Grubbs-Ⅰ catalyst,the polymerization of piperidine-appended spirocyclopropenes was not possible,only the ROCM products were obtained after the vinyl ether was quenched.Under Grubbs-II,Hoveyda-Grubbs-II or Grubbs-II catalysis,Elinear polymers were obtained,and dimer cyclohexadiene molecules are obtained.For its different chemoselectivity and stereoselectivity,we attempted to capture and structure analysis these Ru carbene propagating species during polymerization and clarified their chelation mode.Using Grubbs-Ⅰ,the chain growth of Ru carbene intermediates is difficult due to the high steric hindrance of the substituent groups in the piperidine-appended substituents.While Grubbs-II,Hoveyda-Grubbs-II or Grubbs-Ⅲ catalyzed reaction conditions,the activity of catalyst is relatively high,and chain growth can proceed smoothly to obtain polymer.At the same time,the steric hindrance effect of the substituent is also the fundamental reason for its different chemical selectivity from that ROMP of spirocyclopropene containing an N-aryl substituted azetidine.In addition,the mechanism of stereoselective synthesis of E-configuration polymers under Grubbs-II,Hoveyda-Grubbs-II and Grubbs-Ⅲ catalysts is also proposed.This thesis would like to provide insights into the mechanism of the chemoselective ROMP of spirocyclopropenes using Grubbs catalysts and offer clues for designing new ROMP reactions.