Study On The Selective Desymmetrization Reaction Catalyzed By Nitrogen Heterocyclic Carbene

Urazole is a heteroatom-rich five-membered heterocycle,which receives considerable interest in developing bioactive molecules as potential medicines.In the area of bioactive molecule development,it has been long-established that the chirality of the molecules,including axial chirality,can have profound influence on the activities.Given the wide presence of nitrogen atoms,molecules bearing a chiral C-N axis is of particular interest.Therefore,N-Heterocyclic carbene(NHC)catalyst was used to prepare axially chiral and urazole-containing molecules with high optical purities.We have disclosed an atroposelective [3 + 2] annulation reaction for desymmetrization of 4-arylurazoles.The C-N axis that is remote to the NHC catalyst moiety of the reaction intermediates is efficiently established.Axially chiral pyrazolo[1,2-a]triazole derivatives bearing various substituents and substitution patterns are afforded as the final products in good to excellent yields and enantioselectivities.The stereochemical stability of the axially chiral products is evaluated via thermal dynamic methods.Versatile functional molecules bearing chiral C-N axes can be obtained from the pyrazolo[1,2-a]triazole products in good yields with excellent enantioselectivities.