Semicorrin Metal Complexes as Enantioselective Catalysts. Part 1. Synthesis of Chiral Semicorrin Ligands and General Concepts

Article abstract of DOI:10.1002/hlca.19880710620

An efficient synthesis of chiral semicorrin ligands is described (see 6-9, Schemes 2 and 3).Both enantiomers are readily obtained in enantiomerically pure form starting either from D- or L-pyroglutamic acid (1).Semicorrins of this type possess several features that make them attractive ligands for enantioselective control of metal-catalyzed reactions.Their structure is characterized by C2 symmetry, a conformationally rigid ligand system, and two stereogenic centers adjacent to the coordination sphere.In a metal complex, the two substituents at the stereogenic centers shield the metal atom from two opposite directions and, therefore, are expected to have a pronounced effect on the stereochemical course of a reaction occuring in the coordination sphere.The structure of these two substituents can be easily modified in a variety of ways.A series of (semicorrinato)copper(II) complexes (see 10-14, Scheme 4) has been prepared, and in one case (14), the three-dimensional structure has been determined by X-ray analysis (Fig. 1).