Iridium-Catalyzed Regioselective Hydroboration Of Unactivated Internal Alkenes

Alkyl boronic acid and its derivatives are important building blocks in synthetic chemistry due to their ability in participating in carbon-carbon and carbon-heteroatom bonds forming reactions.In addition,some of them have shown attractive bioactivities.Consesquently,a number of methods have been developed to prepare these structural.Traditional moethods rely on reaction of alkyl lithium or Grignard reagent with boronic esters,which usually suffers from limitations such as harsh reaction conditions and narrow functional group compatibility.On the other hand,transition-metal-catalyzed hydroboration of alkenes has become one of the most convenient and straightforward methods to synthesiz alkyl boronic acids under milder reaction conditions.However,there are still some challenges in this area,for example,regioselective hydroboration of aliphatic internal alkenes.This challgene is mainly caused by similar properties of steric and electronic properties of two substituents of both sides of alkenes.In the current work,we have developed a highly regioselective hydroboration of aliphatic ineternal alkenes using[IrCp*Cl₂]₂ as catalyst.We have screened a series of conditions such as catalyst,ligand,solvent,temperature,catalyst loading,amount of HBpin,etc.Finally,we determined the optimal conditions is:1 mol%of[IrCp*Cl₂]₂,2 mol%of Xantphos,and 1.0 equiv of HBpin in 1,4-dioxane for 12 h at room temperature.This reaction could tolerate a wide range of functional groups with excellentγ-selectivityup to 99%).