ACADEMIA ROMÂNĂ Revue Roumaine de Chimie http://web.icf.ro/rrch/ Rev. Roum. Chim., 2010, 55(8), 455-458 NOVEL N-O TYPE OXAZOLINE LIGANDS Duygu ERGUNES, Zeynep KOKCE, Okan SIRKECIOGLU and Naciye TALINLI * Istanbul Technical University, Faculty of Science and Letters, Department of Chemistry, 34469 TR, Istanbul-Turkey Received September 22, 2009 We describe here the synthesis of three novel N-O type oxazoline compounds from readily available 3-hydroxy-2-naphthoic acid and pamoic acid (BINOL–box type) and 2-naphthol (Xabox type). INTRODUCTION ∗ Metal complexes of C 2 -symmetry ligands have gained a reputation as efficient chiral catalysts in enantioselective catalytic transformations. In particular, chiral bisoxazolines (Box) have found broad use as chiral ligands due to their versatility and easy preparation. They have been used in a large number of asymmetric reactions. For instance, metal complexes of chiral bisoxazolines have been used in enantioselective cyclopropanation, allylic alkylation, Diels-Alder cycloaddition, oxidative addition reaction etc. 1-5 On the other hand, catalysis by dinuclear transition metal complexes of oxazoline ligands have the potential of catalyzing a reaction more efficiently or stereoselectively than mononuclear metal complexes. Mixed-metal systems offer the possibility for selective activation of two different reactants. Dinuclear metal complexes generally contain tetradentante nitrogen ligands. 6,7 RESULTS AND DISCUSSION We present herein some preliminary results on new types of mono and bisoxazoline ligands starting from 2-naphthol, 3-hydroxy-2-naphthoic acid and pamoic acid respectively (Figure 1). In order to synthesize compound 1, 3-hydroxy-2- naphthoic acid was reacted with glyoxalaldehyde ∗ Corresponding author: talinlin@itu.edu.tr bisulfite in formic acid. 8 The carboxylic acid derivative was turned into acid chloride, and reacted with ethanolamine to get access to hydroxyamide compound that was cyclized in the presence of diethylaminosulfur trifluoride (DAST) to obtain bisoxazoline 1a (Scheme 1). 9,10 In the cis-7a,14c-dihydro-3,12-7,8- dioxa[6]helicene 1a aromatic rings are not co-planar because interconversions of the enantiomers is observed in solution 11 . Compound 1a can act as a chiral and tetradentate (N-O-O-N) or bidentate N-O ligand . The oxazoline rings are apart from each other which may allow the ligand to bind two metal atoms with each N-O. As mentioned before, this kind of dinuclear metal complexes have been a subject of great interest since there are examples in which dinuclear metal complexes catalyze the reactions more efficiently than the mononuclear ones. 6,7 Bisoxazoline 2 was derived from pamoic acid and (R)-phenylglycinol. This BINOL-box type compound also has the possibility of combining two metal atoms like the ligand 1a. However, in compound 2 chirality comes from oxazoline groups. Since phenolic salts have very poor solubility in organic solvents, in order to avoid potassium salt of the end product, we preffered Vorbrüggen method 12-14 (scheme 2) for synthesizing the compound 2. By using Vorbrüggen method, it is possible to get oxazolines in one step reaction but, the large excess of triphenylphosphine that had to be used made