N-heterocyclic Carbene-palladium (?)-1-Methylimidazole Complex Catalyzed Suzuki-Miyaura Coupling Of Benzyl Esters

Diarylmethanes have important applications in industry and medicine.They are mainly prepared from the Suzuki-Miyaura coupling of benzyl halides.However,due to the instability of benzyl halides and toxicity of the halides-containing by-products,to find out more suitable electrophilic reagents are necessary.During the past years,the O-based alternative electrophiles have attracted much attention because they are more easily available from phenol derivatives or carbonyl enolates and they are also sometimes cheaper.In addition,the use of O-based electrophiles instead of their halides counterparts will thus throw away the toxic halides-containing by-products.However,no paper was reported on the Suzuki-Miyaura coupling of benzyl sulfonates and dimethylaminocarbanates to date.This thesis mainly introduced the N-heterocyclic carbene-palladium(?)-1-methylimidazole [NHC-Pd(?)-Im] complex catalyzed Suzuki-Miyaura coupling reaction of benzyl esters including tosylates,mesylates and dimethylaminocarbamates,which can be divided into two parts:1.The first example of NHC-Pd(?)-Im complex catalyzed Suzuki-Miyaura coupling between benzyl sulfonates and arylboronic acids was reported.Under the optimal conditions,all reactions worked well to give the desired products in good to almost quantitative yields under the optimal conditions.Electron-rich,-neutral,-poor and sterically-hindered substituents on both substrates are tolerated in such transformation,providing a convenient,efficient and alternative method for the synthesis of diarylmethanes.2.The first example of NHC-Pd(?)-Im complex catalyzed Suzuki-Miyaura coupling of benzyl dimethylaminocarbamates with arylboronic acids was achieved in an environmentally benign medium.Using water as the sole solvent,such transformation took place very well to give the desired diarylmethanes in good to almost quantitative yields under mild conditions.It is worthy of noting here that this is the first example of benzyl dimethylaminocarbamates used in coupling reaction,thus affording a new method for the formation of diarylmethanes by palladium-catalyzed C-O bond activation.