[reaction: see text] Racemic 1,2-diols and alpha-hydroxy carbonyl compounds can be asymmetrically benzoylated in a kinetic resolution in the presence of various Cu(II)-aza(bisoxazoline) catalysts. A novel bisbenzyl-substituted aza(bisoxazoline) ligand proved to be especially effective when immobilized on MeOPEG(5000), giving from 91 to > or = 99% ee in 37-49% yield for each of five sequential reactions.

Phosphorus dendrimer immobilized azabis(oxazoline) ligands can be efficiently synthesized up to the third generation with 48 ligand molecules being attached to the periphery using click chemistry. The so-assembled macromolecules were evaluated in copper(II)-catalyzed asymmetric benzoylations, showing good yields and enantioselectivities. Moreover, the copper(II)-catalysts could be readily recovered and reused in several cycles. The globular structure of the dendritic ligands seems to prevent interference of the triazole moieties in the catalysis, contrasting MeOPEG or polystyrene bound ligands of the same type.

Aza(bisoxazoline) ligands were attached to various polymeric supports and the resulting immobilized ligands were evaluated in copper(I)-catalyzed asymmetric cyclopropanations. The efficiency of these transformations depends greatly on the polymeric support, on the protocol being applied for the immobilization of the ligands, and on the preparation of the catalysts.

A thorough experimental and theoretical study of the enantioselective cyclopropanation of alkenes catalyzed by chiral bis(oxazoline)- and azabis(oxazoline)-copper complexes, which comprise a new family of ligands that lack C2 symmetry, has been conducted. Surprisingly high enantioselectivities were observed with some of these ligands, which were rationalized on the basis of molecular modeling studies. The course of the asymmetric induction in connection with ligand symmetry and the implications for supported enantioselective catalysts are discussed.

Simple bis(oxazoline) ligands, especially azabis(oxazolines), can promote the copper(II)-catalyzed Michael addition of indoles to benzylidene malonates with up to >99 % ee (ee=enantiomeric excess), provided that the ligand/metal ratio is tuned meticulously with particular regard to the electronic properties of the substrate. Despite a common paradigm followed in many asymmetric catalyses, an excess of chiral ligand is not always beneficial. In fact any excess of ligand has to be avoided to reach excellent enantioselectivities when electron-rich benzylidene malonates are used. On the contrary, malonates carrying an electron-withdrawing group require an excess of ligand for an optimum ee value. A correlation of optical yields versus the sigma(I) values of several para substituents shows a sigmoid trajectory. In the presence of an additive, such as triflate, the significance of the ligand/metal ratio vanishes and very good enantioselectivities are achieved at any rate--no matter whether electron-donating or withdrawing substituents are present.

Palladium-azabis(oxazoline) complexes proVed to be highly selectiVe and efficient in the asymmetric copolymerization of styrene and CO at ambient pressure.Stereoregular polymers, like isotactic polypropylene, have changed the world due to their extraordinary material properties. Such polymers possess mirror planes and are consequently not chiral. Nevertheless, metal-promoted polymerization using chiral catalysts has proved to be the most powerful tool to achieve the stereocontrolled synthesis of these macromolecules. 1

Cyclopropane derivatives Q 0021Synthesis of Polymer-Bound Azabis (oxazoline) Ligands and Their Application in Asymmetric Cyclopropanations. -The catalyst derived from BOA and Cu(I) under optimal conditions gives the best results in the enantioselective cyclopropanations of aromatic alkenes and also exceeds the results achieved with non-polymer-bound azabis(oxazolines). -(WERNER, H.; HERRERIAS, C. I.; GLOS, M.; GISSIBL, A.; FRAILE, J. M.; PEREZ, I.; MAYORAL, J. A.; REISER*, O.; Adv. Synth. Catal. 348 (2006) 1-2, 125-132; Inst. Org. Chem., Univ. Regensburg, D-93053 Regensburg, Germany; Eng.) -Klein 22-063

Stereochemistry O 0030Cu (II)-Aza(bisoxazoline)-Catalyzed Asymmetric Benzoylations. -Among all ligands (I)-(IV) tested, the best results are presented in the scheme. -(GISSIBL, A.; FINN, M. G.; REISER*, O.; Org. Lett. 7 (2005) 12, 2325-2328; Inst. Org. Chem., Univ. Regensburg, D-93053 Regensburg, Germany; Eng.) -Nuesgen 42-031