Design of Chiral Hydroxyalkyl- and Hydroxyarylazolinium Salts as New Chelating Diaminocarbene Ligand Precursors Devoted to Asymmetric Copper-Catalyzed Conjugate Addition

The design and the synthesis of a set of new chiral hydroxyalkyl- and hydroxyaryl-chelating diaminocarbene ligands is reported. Comparative catalytic studies show the importance of the scaffold design around the NHC unit to obtain a high enantiocontrol in Cu-catalyzed asymmetric conjugate addition (ACA). Whereas low selectivities are observed when the stereogenic centre is placed within the N-heterocyclic ring, an interesting match effect can be observed when central chirality is located within both of the two side chains, which enables up to 92 % ee in the catalysis reaction. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)