Semicorrin Metal Complexes as Enantioselective Catalysts. Part 1. Synthesis of chiral semicorrin ligands and general concepts

TLDR: In this article, an efficient synthesis of chiral semicorrin ligands is described and a series of (semicorrinato)copper(II) complexes has been prepared, and in one case the three-dimensional structure has been determined by X-ray analysis.

Abstract: 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 occurring 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).