Cobalt-Catalyzed Remote Hydroboration And Isomerization Of Vinyl Ethers

Alkylboronate eaters have received much attention because of their reactivities and stability.However,remote hydroboration involving alkene isomerization or chain walking remains underdeveloped.In recent years,although some progress has been made,the current methods suffer from a substrate limitation.For example,the use of internal alkenes bearing heteroatoms（O,N,S,etc.）on the chain remains challenging and scarce.Therefore,the development of new methods to address this limitation is in high demand.This dissertation describes a ligand-controlled cobalt-catalyzed remote hydroboration and alkene isomerization of vinyl ethers.When the dcype ligand（1,2-bis（dicyclohexylphosphino）ethane）is used,the remote hydroboration reaction occurs to generate alkylboronate silyl ethers,when the xantphos ligand（4,5-bis（diphenylphosphino）-9,9-dimethylxanthene）is used,the formation of silyl enol ethers is favored.The reaction has the following advantages:（1）a cheap base-metal catalytic system,high efficiency,a broad substrate scope,good functional group tolerance as well as the reaction conditions are simple.（2）The direction of chain walking can be changed by regulating the ligand.（3）The remote migration hydroboration reaction can be scaled up to the gram scale,the product has a wide range of applications.1.The cobalt-catalyzed remote hydroboration reaction of allylic siloxanes was realized,a variety of alkylborate oxysilane was synthesized.The reaction uses 1mol%Co（acac）₂ and dcype as catalytic system,HBpin as boron source and octane as solvent for 12 hours at room temperature in N₂ atmosphere.The reaction conditions are simple,and no additive participation is required.A range of linear,branched,aryl group-terminated allylic siloxanes were also viable substrates.This protocol features easy gram-scale preparation,alkylboronate was successfully converted into other C–O,C–Br,C–N,and C–C bonds by various C–B bond transformations.Preliminary mechanistic studies suggest that the remote hydroboration reaction goes through a tandem chain walking/hydroboration process.2.Ligand-controlled cobalt-catalyzed alkene isomerization of allylic siloxanes to synthesize silyl enol ethers was realized.The reaction still uses Co（acac）₂ as the catalyst,by changing the ligand to xantphos,DME as the solvent,adding a catalytic amount of additive CF₃COONa,and reacting at 60℃for 12 hours under N₂ atmosphere.This protocol features a broad substrate scope and good functional group tolerance.