N-Heterocyclic Carbene Catalyzed Regioselective Umpolung Of Alkynyl Aldehydes And Asymmetric Catalysis Via Activation Of Esters

This thesis makes a description of N-heterocyclic carbene catalyzed regioselective umpolung of alkynyl aldehydes and asymmetric catalysis via activation of esters.It consists of three chapters:First chapter was the literature review,which introduced the background,properties and application of the regioselective umpolung of alkynyl aldehydes and ester activation.Second chapter was investigation on the N-heterocyclic carbene catalyzed regioselective umpolung of alkynyl aldehydes:N-Heterocyclic carbene was successfully used as organic catalyst for the regioselective umpolung(a1-d1 and a3-d3)of alkynyl aldehydes.The regioisomeric products were obtained from the same substrates.After optimization reaction condiotions,formal[3+2]annulation of alkynyl aldehydes and nitrosobenzenes via a1-d1 umpolung gave 2,5-disubstituted isoxazol-3(2H)-ones efficiently,while moderate yields were obtained via a3-d3 umpolung.These two kinds of products are skeletons of some of the biologically active compounds and materials.Also,the possible mechanism was investigated via deuterium experiments.The third chapter was the studying on the asymmetric catalysis via activation of esters:Turn waste into treasured strategy was used successfully under N-heterocyclic carbene(NHC)catalysis followed by N-hydroxyphthalimide(NHPI)catalysis and this mode made the combination of the NHC chemistry and NHPI chemistry together.First,N-heterocyclic carbene was performed as nuclephilic catalyst for the asymmetric[4+2]cyclization of esters and a,?-unsaturated imines.Lower catalyst loading and less amount of base were used and it was performed well under additive free condition.Then,upstream waste NHPI acted as downstream catalyst for the N-to C-sulfonyl migration for the main product and enantiomeric excess were maintained under radical conditions,which fill the blank of the application of the concept in the N-heterocyclic chemistry.