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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.

[Structure: see text] Simple bis(oxazoline) ligands, especially azabis(oxazolines), can catalyze the copper-catalyzed addition of indoles to benzylidene malonates in up to >99% ee, provided that excess of chiral ligand is avoided. The paradigm followed in many asymmetric catalyses that an excess of chiral ligand with respect to the metal should improve enantioselectivity because a background reaction by free metal is suppressed, is not applicable here, which might call for revisiting some of the many copper(II)-bis(oxazoline)-catalyzed processes known.

[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 toor = 99% ee in 37-49% yield for each of five sequential reactions.

Simple bis(oxazoline) ligands, especially azabis(oxazolines), call 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 all electron-withdrawing group require an excess of ligand for all Optimum ee value. A correlation of optical yields versus the sigma(I) values of several para substituents shows a signioid trajectory. In the presence of in 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.

10 pages, 9 figures, 3 tables, 2 schemes., 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., This work was made possible by the financial support of the Ministerio de Educación y Ciencia (projects CTQ2005–08016 and Consolider Ingenio 2010 CSD 2006–00). I.V. and M.R. thankthe Ministerio de Educación y Ciencia and the Diputación General de Aragón for grants, respectively.

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.

This workw as supported by the Fonds der Chemischen Industrie, the DAAD (Acción Integrada HA2001 – 0096), the C.I.C.Y.T. (project PPQ2002– 04012), the DGA, and through generous chemical gifts by Degussa AG. I.P. is indebted to the MEC for a grant.

Palladium−azabis(oxazoline) complexes proved to be highly selective and efficient in the asymmetric copolymerization of styrene and CO at ambient pressure.

A straightforward synthesis of chiral aza-bis(oxazoline) (Azabox) ligands from commercially available amino alcohols is described. The new protocol allows access to previously reported Azabox ligands in considerably improved yields but also to new derivatives, including non-C2-symmetrical ones.