Copper (II) in organic synthesis. XI. Evaluation of the ligand architecture on the efficiency of a copper (II) catalyst for enantioselective Michael reactions

Several bis-copper (II) complexes with chiral ligands derived from 2-substituted 2-(salicylideneamino) ethanols have been tested as catalysts of enantioselective Michael reactions. The degree of enantioselection is strongly affected by the architecture of the ligand. The best result (75% e.e.) was obtained for a ligand having a substituent potentially suitable to induce the formation of a bis-tetradentate copper (II) complex with a square pyramidal coordination.