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

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  • We thank Dr. Hans-Ulrich Blaser for helpful discussions. Generous financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged. The research of F.G. is supported by the Alfried Krupp Prize for Young University Teachers of the Alfried Krupp von Bohlen und Halbach Foundation.

Abstract

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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.

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