Asymmetric <i>gem</i>‐Hydroboration and <i>gem</i>‐Hydrogenation of Ynamides: A New Gateway to Chiral Fischer Carbene Complexes and their Catalytic Transformations

Ynamides, when reacted with H₂ or HBpin in the presence of [Cp*RuCl]₄, convert into chiral-at-metal Fischer carbenes by regioselective gem-hydrogenation or gem-hydroboration of the polarized triple bond, respectively. gem-Hydroboration concomitantly affords a carbogenic borylated stereocenter adjacent to the ruthenium carbene unit, the configuration of which can be controlled using an Evans auxiliary. These are the first examples of asymmetric gem-addition reactions to alkynes known in the literature; representative pianostool ruthenium carbene complexes formed by this unconventional route were characterized by crystallographic and spectroscopic means. They undergo various stoichiometric reactions and can even entertain catalytic asymmetric transformations, such as hydrogenative cyclopropanations or a novel type of borylative cycloisomerization.