Application Of N-Heterocyclic Carbenes As Base Catalysts And Cobalt Ligands

In recent years,N-heterocyclic carbenes(NHCs)have received considerable attention as an important class of organocatalysts and ligands in organic chemistry field.As a special class of organocatalysts,NHCs have been widely used in umpolung reactions of aldehyde compound,however,the reactive substrate of this mode is confined to the aldehyde compound.Therefore,chemists have begun to explore new types of reaction substrate,so as to expand the catalytic mode of NHCs.As one of new catalytic modes,which is using NHCs as general base catalysts,is still at exploratory stage.In addition,as a class of versatile ligands,NHCs are employed as new generation catalysts in transition noble metal catalysis.Therefore,exploring the new catalytic modes using NHCs as base catalysts and expanding the reactions catalyzed by inexpensive cobalt/NHC are promising from academic viewpoint and practical application.Our research concentrates on the application of NHCs as base catalysts and cobalt ligands.The main work is described as follows:N-heterocyclic carbene precursors are applied in the reaction of ?-alkylation of ketones with primary alcohols.With the assistance of a base,these N-heterocyclic carbenes can catalyze the reaction smoothly to furnish dialkylated ketones in good yields(up to 98%).The significant features of this method include high atom economical,operational simplicity,and no need of transition metals and ligands.The direct C-3 alkylation of indoles with alcohols through N-heterocyclic carbene is described.With the assistance of a base,C-3 benzylated indoles could be obtained not only with primary alcohols,but also with second alcohols in moderate to good yields.The significant features of this method include high atom economical,high regioselectivity,low-cost and environmentally benign.Quinolines have been obtained through the indirect Friendlander annulation starting from 2-aminobenzyl alcohol and ketones catalyzed by N-heterocyclic carbene,and the synthesis of polysubstituted quinolines through a one-pot,two-step tandem reaction starting from readily available ketones and alcohols via alpha-alkylation andindirect Friedlander annulation under air also has been presented.The method can avoid products containing toxic metals,makes it a choice for the pharmaceutical and chemical industries.A NHC catalyzed domino aza-Michael/aldol reaction of ?-ketoamides with a,?-unsaturated ketones have been realized.The domino reaction proceeded smoothly,affording pharmaceutically important 3-hydroxypyrrolidinones in good to excellent yields with excellent functional group tolerance.The reaction features a transition-metal-free approach,mild reaction conditions,the relative stability of the domino products as well as a simple procedure.A newly developed process for direct C-H functionalization of heteroarenes with ethyl bromodifluoroacetate catalyzed by cobalt catalyst has been disclosed with the use of a N-heterocyclic carbene ligand.The methods take place at the C-H bonds adjacent to the heteroatoms.It is applicable to a variety of heteroarenes and delivers the corresponding products in moderate to good yields with high regioselectivity.