Deracemization of Chiral-at-Ruthenium Catalyst by Diastereoselective Dynamic Resolution

Abstract

In this work, we introduce an auxiliary-mediated deracemization protocol in the synthesis of a non-C2-symmetric chiral-at-ruthenium catalyst bearing two cyclometalated 7-methyl-1,7-phenanthrolinium heterocycles, a CO ligand, and an additional labile MeCN ligand. Upon coordination of a monodentate chiral oxazoline ligand as chiral auxiliary, the racemic complex mixture is transformed into a single diastereomer in quantitative yield via a diastereoselective dynamic resolution process. After removal of the oxazoline ligand under acidic conditions, enantiomerically pure complexes (>20:1 er) with a Δ-and Λ-configuration were obtained. An application of the chiral-at-ruthenium catalyst to an enantioselective ring-closing C(sp3)-H amidation of a 1,2,4-dioxazol-5-one to the corresponding chiral γ-lactam is demonstrated.