synthesis and catalytic activity of two new cyclic tetraaza ligands合成和催化活性的两个新的循环tetraaza配体.pdf

Molecules 2003, 8, 453-458 molecules ISSN 1420-3049 / Synthesis and Catalytic Activity of Two New Cyclic Tetraaza Ligands María Hechavarría Fonseca, Thomas Hjelmgaard a and Burkhard König * Institut für Organische Chemie, Universität Regensburg, D-93040 Regensburg, Germany, Fax: (+49) 941-943-1717. a Current address: Department of Chemistry, Technical University of Denmark, Denmark * Author to whom correspondence should be addressed; e-mail: burkhard.koenig@chemie.uni- regensburg.de Received: 11 April 2003; in revised form: 9 May 2003 / Accepted: 9 May 2003 / Published: 31 May 2003 Abstract: Two new chiral cyclic tetraaza ligands were synthesized and characterized. Their catalytic activity was tested in the asymmetric addition of diethylzinc to benzaldehyde. The expected secondary alcohol was obtained in moderate yields, but with very low enantioselectivity. Keywords: Chiral tetraaza ligands; asymmetric catalysis. Introduction The importance of nitrogen-containing ligands as catalysts for many asymmetric transformations has grown in the last years [1] because of their high stability, easy preparation and promising results [2]. In 1969 Uhlemann developed the synthesis of a new chiral Schiff base 1 from o-amino- benzaldehyde and 1,2-cyclohexanediamine [3]. Compounds containing this optically active trans- cyclohexane-1,2-diamine moiety have proven to be very useful in both asymmetric synthesis [4] and diastereomeric recognition of peptides [5]. Molecules 2003, 8