Iridium-Catalyzed Regioselective Hydroboration Of ?-Substituted Allylic Amides

Alkyl borates are an important building block in organic synthesis.They are often used in the construction of carbon-carbon and carbon-heteroatom?oxygen,nitrogen,halogen,etc.?bonds,and have been found widespread applications in materials and synthetic chemistry.Meanwhile,alkyl borates are important bioactive compounds and pharmaceutical intermediates.Among them,alkyl pinacol borates has been receiving widespread attention in synthetic chemistry,due to their good stability and insensitive to air and water.Traditional methods rely on reaction of organometallic reagent such as lithium reagent or Grignard reagent with boronic esters to prepare alkylboronic acid compounds,suffer from limitations such as narrow functional group compatibility and harsh reaction conditions.Transition-metal-catalyzed hydroboration of alkenes provide a simple,efficient,and atomically economical method for obtaining alkylboronic acid compounds with broad functional groups and diverse structures.Transition-metal-catalyzed hydroboration of alkenes are recently concentrated in terminal alkenes,activated alkenes and styrene derivatives.The regioselective hydroboration reaction of aliphatic internal alkenes is still a challenging problem,which is mainly caused by difficulty in the differentiation of two sterically and electronically similar alkene substituents.Therefore,it is of great significance to develop regioselective hydroboration of internal alkenes.Recently,we have developed iridium-catalyzed?-selective hydroboration of?-substituted allylic amides.[Ir Cp^*Cl₂]₂ was found to be a highly efficient catalyst for this reaction without ligands,which combined with HBpin?1.6 equiv?as the hydroboration reagent,and in the presence of 1,1-diphenylethene?1.0 equiv?as additive,giving the corresponding products in high yield.A variety of functional groups could be well-tolerated,affording?-borylated products in good yields with 80-97%?-selectivity.