Ligand‐Controlled Highly Regioselective and Asymmetric Hydrogenation of Quinoxalines Catalyzed by Ruthenium N‐Heterocyclic Carbene Complexes

Abstract

Inflating flat bicycles: Proper choice of the N-heterocyclic carbene (NHC) ligand in Ru NHC complexes allows the completely regioselective ligand-controlled hydrogenation of either the heterocyclic or the carbocyclic ring of a substituted quinoxaline in quantitative yields. Chiral NHC ligands allow the challenging asymmetric hydrogenation of the carbocyclic ring of quinoxalines, yielding enantioenriched 5,6,7,8-tetrahydroquinoxalines with an enantiomeric ratio of up to 94:6.