Preparation Of N-Heterocyclic Carbenes Containing Adamantyl Group And Their Applications In Organic Catalysis

Carbene is a type of high active catalyst and plays an important role in modern chemical industry.Similar to the general structure of carbene,N-heterocuclic carbene(NHC)is also an electroneutral compound,and is widely used in the umpolung reaction of aldehydes because of its structural diversity.However,There are some limitations in the selection of products,so chemists are dedicated to exploring new carbene structures.Adamantane-contained ligands are often ued in a variety of reactions because of the rigidity,stability and electron-donating nature of adamantane motif.Therefore,it is of theoretical significance and practical value to introduce adamantane moiety into the NHC structure.In this dissertation,the syntheses and applications of several NHCs containing adamantane were investigated.The main work is described as follows:The synthesis of a spirocyclic alkylamino carbene containing two adamantyl groups was attempted first but failed to give target product.Then,two substituted imidazole carbene precursors containing two aromatic substituents and that containing two adamantyl groups,and dihydro imidazole carbene precursor were successfully synthesized.After that,a novel unsymmetrical NHC containing one adamantane ring was designed and synthesized.Finally,a bicyclic triazole onium was prepared via a modified route.The as-prepared carbenes were used to catalyze the lactonization of dienals with aromatic aldehydes.The results indicated that the unsymmetrical 1-adamantyl-3-mesitylimidazolium chloride showed the highest catalytic activity.Under the optimized reaction conditions,a series of y-butyrolactones were obtained in excellent yields up to 90%and with satisfactory selectivities up to 14:1(cis:trans).The coordinations of 1,3-diadamantyl-4,5-dihydroimidazolium chloride derived carbene to Cu(I)and Ni(II)were investigated.The reaction between the chloride salt with cuprous chloride in presence of potassium tert-butoxide did not generate the corresponding coordination product,but afforded 1,3-diadamantyl-4,5-dihydroimidazolium dichlorocuprite,The product was characterized by NMR and single crystal diffractometer.Treating the imidazolium chloride with LDA at low temperature(-78 ?)and reacting with nickel acetylacetonate gave no coordination product neither,only oxidation by-product 1,3-adamantyl imidazolidinone was obtained.The obtained 1,3-diadamantyl-4,5-dihydroimidazolium dichlorocuprite was applied to the aerobic oxidation of benzyl alcohol,however,moderate yield of benzaldehydes were achieved due to its low stability.The introduction of adamantane skeleton into NHC molecule is a new idea for carbene chemistry.When two adamantly groups are present in NHC,the reactivity of the derived carbene would decrease because of too high steric hindrance,and it would make coordination with metal more difficult.In comparison,the NHC bearing only one adamantly group possesses some advantages such as good stability,high catalytic activity and excellent seteroselectivity.This work provides new idea for the design and synthesis of more active and selective carbene catalysts.