Palladium-catalyzed Cyclobutanation Of Aryl Sulfonates With Norbornenes And Arylalkynylation Of Norbornenes

Phenol derivatives are lower toxic,stable and abundant in nature,thus their transformation and appli cation have attracted attention of synthetic scientists.Studies show that phenol derivatives can be used as the effective electrophiles instead of organic halides,coupling with organometallic compounds(B,Mg,Zn,etc)or Z-H compounds(Z = C,N and P)t o build new C-C or C-Z bonds.C-H activation directed by phenoxides is also widel y applied in organic synthesis.Herein,we report a cyclobutanation of phenol derivatives with norbornenes to synthesize benzocyclobutanes.In this palladium-catal yzed reactri on,C-O and C-H bonds are activated in one pot.Meanwhile,we utilize aryl sulfonates as aryl sources and terminal alkynes as alkyne sources to realize arylalkynylation of double bonds in norbornenes forming 2,3-disubstituted norbornene compunds.As for the traditional synthesis of these compounds,alkylation reagents are mainly limited to the toxic organostannes and aryl terminal alkynes,while the electrophiles inevitably were aryl haildes.Moreover,reactions were conducted under harsh conditions with lo w yields.The specific research contents and results are as follows :(1)Pd-catal yzed cyclobutanation of aryl sulfonates(activated triflates,relativel y inert p-toluenesulfonates and mesylates)with norbornenes via dual C-O and C-H activation in one pot.The substrate scope for both phenol derivatives and norbornenes were general.Phenol derivatives from bioactive molecules such as eugenol,methyl vanillate,hordeine and raspberry ketone work well under the reaction conditions.When the reaction is conduc ted at gram-scale,only 0.4 mol % Pd catal yst is required.These results well demonstrated the potential synthetic value of this reaction in organic synthesis.(2)Pd-catal ysted arylalkynylation of double bonds in norbornenes with the use of aryl triflates as the aryl sources and terminal alkynes as the alkyne sources.Aliphatic chain alkynes,circular alkynes and heteroaryl alkynes are all applicable to this reaction to generate the corresponding difunctionalization product in high yields.This reaction co nditions were relatively mild and tolerant to a series of substrates,and it was a new method to synthesize 2,3-disubstituted norbornene compounds,the analogues of Prostaglandin.