Study On Cyanation Reaction Catalyzed By N-Heterocyclic Carbene

The past decade has witnessed a dramatic growth in organocatalysis chemistry. As one class of versatile nucleophilic organocatalyst, NHCs have been utilized broadly in a variety of important transformations such as Umpolung, cycloaddition,Polymerization and other reactions. However,there is few research reported about addition reaction catalyzed by NHCs. In this article we would like to discourse the NHCs be used as efficient catalysts for the cyanation reaction of aldehydes, aldimines and ketones with ethyl cyanoformate and acetyl cyanide respectively which substituted the high toxic compound as HCN,TMSCN. A novel organic catalysis method for cyanation reaction has been developed.In the first part, the optimization experiments were carried out by use ethyl cyanoformate and acetyl cyanide as cyanide resouse and NHCs as catalysts. The results showed that ethyl cyanoformate and acetyl cyanide can be catalyzed well with aldehydes. With the optimal reaction conditions in hand, 19 and 18 aldehydes were evaluated for the reaction respectively and the results indicated the reaction between ethyl cyanoformate and aldehydes can be ended in quantitative yield within short times,the highest yield is 99% and the catalyst load is only 1%. When catalyst load added to 10 %, acetyl cyanide and aldehyde can reacted well and the highest yield is 90%. The products of the reaction can be easily hydrolysis and obtain theα- cyanohydrin.In the second part, the cyanation of aldimines named Strecker reaction was examined. Fourteen aldimines were synthesized and reacted with cyanide source to obtain the correspondingα-amino nitriles. It was found that both aromatic and aliphatic aldimines were suitable electrophiles. When reacted with ethyl cyanoformate the highest yield is 93% while reacted with acetyl cyanide the highest yield is 76%.In the third part, we decided to investigate the catalytic cyanation reaction of ketones and ketimines in order to expand the scope of this cyanation and construct tetrasubstituted carbon. When we found the reaction between acetophenone and ethyl cyanoformate or acetyl cyanide can't be generated, we refer toα-keto esters, 2, 2, 2-trifluoro-1-phenylethenone and ketimines. The compounds likeα- keto esters reacted well and gained a good yield contrasted with compounds like 2, 2, 2-trifluoro-1-phenylethenone and ketimines.The latter get only a poor yield. In summary, we have demonstrated a new method for NHCs-catalyzed cyanation reaction of aldehydes, imines and ketones with ethyl cyanoformate or acetyl cyanide and obtain lots of important compouds likeα- cyanohydrin,α-amino nitriles and cyanide with tetrasubstituted carbon. These cyanation reactions afford the corresponding products in good yields under mild reaction conditions and the subsrates of this reaction can be extended to a broad scope.