One‐Pot Cobalt‐ or Copper‐Catalyzed Asymmetric Ring‐Opening Hydrosilylation/Hydroboration of Arylidenecyclopropanes

An operationally convenient cobalt-catalyzed one-pot one-step hydrosilylation/hydroboration reaction of arylidenecyclopropanes is developed to access racemic 1,4-borylsilylalkanes. In addition, the corresponding asymmetric reaction is developed with a chiral copper catalyst to prepare 1,4-borylsilylalkanes with high enantioselectivity by a one-pot two-step procedure. Mechanistic studies reveal that this difunctionalization process begins with metal-hydride-catalyzed ring-opening hydrosilylation of arylidenecyclopropanes to generate homoallylsilane intermediates, followed by regio- or enantioselective metal-hydride-catalyzed hydroboration of homoallylsilanes to produce skipped borylsilylalkanes. Selective transformations of C-B and Si-H bonds in skipped borylsilylalkane products are also demonstrated.