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

Abstract

AbstractAn 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).