In palladium-catalyzed alkylations of allylic acetates with malonate as nucleophile, catalysts with oxazoline ligands bearing hydroxymethyl substituents in 4-position have been shown by density functional theory computations to undergo a conformational change on nucleophilic attack, which is accompanied by reduction of Pd(II) to Pd(0). The conformations of the Pd(0) complexes were shown to be governed by the presence of a hydrogen bond with the metal center acting as a hydrogen bond acceptor. The conformational change, which is absent in catalysts with O-alkylated analogs, largely affects the enantioselectivity of the catalytic process. This process is a previously uninvestigated example of where this type of weak hydrogen bond has been shown to influence the stereochemistry of a chemical reaction.

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Chiral pyridinooxazoline, quinolinooxazoline, bis(oxazolino)pyridine (pybox), and bisoxazoline (box) derivatives containing crown ether residues were prepared. Some of the ligands were assessed in substrate binding studies and in palladium catalyzed allylic alkylations.

First to fourth generation dendritic substituents based on 2,2-bis(hydroxymethyl)propionic acid and (1R,2S,5R)-menthoxyacetic acid were attached to 2-(hydroxymethyl)pyridinooxazoline and bis[4-(hydroxymethyl)oxazoline] compounds. The new ligands obtained were assessed in palladium-catalyzed allylic alkylations. The first type of ligands exhibited enantioselectivity similar to that of a benzoyl ester derivative, whereas the latter type of ligands afforded products with higher selectivity than the analogous benzoyl ester. The activity of the dendritic catalysts decreased with increasing generation.

Metal complexes of chiral oxazoline derivatives immobilized on soluble as well as insoluble supports serve as versatile asymmetric catalysts in a variety of applications. In a few cases recovery and reuse of the chiral ligands have been achieved.

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Oxidation of primary and secondary aliphatic and secondary benzylic alcohols into their corresponding aldehydes and ketones was achieved in good yields with palladium catalysts using air as the reoxidant of palladium. The use of palladacycle 1 resulted in higher yields and a faster reaction than the use of Pd(OAc)(2) as the palladium source.

A chiral bis(oxazoline) was grafted on ArgoGel and used in the palladium-catalysed substitution of (±)-1,3-diphenyl-2-propenyl acetate with dimethyl malonate. The enantioselectivity was the same as that observed when the analogous monomeric catalyst was used (94–95% e.e.), despite the fact that the C2 symmetry of the ligand was affected when coupled to the polymer. The polymer-supported catalyst could be recycled several times after removal of precipitated Pd(0). The polymer-bound bis(oxazoline) was also applied in a zinc-catalysed Diels–Alder reaction but lower selectivity and reactivity than the monomer was observed.

This thesis deals with the design of ligands for efficientasymmetric catalysis and studies of the conformation of theligands in the catalytically active complexes. All ligandsdeveloped contain chiral oxazoline heterocycles.The conformations of hydroxy- and methoxy-substitutedpyridinooxazolines and bis(oxazolines) during Pd-catalysedallylic alkylations were investigated using crystallography,2D-NMR techniques and DFT calculations. A stabilising OH-Pdinteraction was discovered which might explain the differencein reactivity between the hydroxy- and methoxy-containingligands. The conformational change in the ligands due to thisinteraction may explain the different selectivities observed inthe catalytic reaction.Polymer-bound pyridinooxazolines and bis(oxazolines) weresynthesised and employed in Pd-catalysed allylic alkylationswith results similar to those of monomeric analogues;enantioselectivities up to 95% were obtained. One polymer-boundligand could be re-used several times after removal of Pd(0).The polymer-bound bis(oxazoline) was also used in Zn-catalysedDiels-Alder reactions, but the heterogenised catalyst gavelower selectivities than a monomeric analogue.A series of chiral dendron-containing pyridinooxazolines andbis(oxazolines) were synthesised and evaluated in Pd-catalysedallylic alkylations. The dendrons did not seem to have anyinfluence on the selectivity and little influence on the yieldwhen introduced in the pyridinooxazoline ligands. In thebis(oxazoline) series lower generation dendrimers had a postiveon the selectivity, but the selectivity and the activitydecreased with increasing generation.Crown ether-containing ligands were investigated inpalladium-catalysed alkylations. No evidence of a possibleinteraction between the metal in the crown ether and thenucleophile was discovered.A new type of catalyst, an oxazoline-containing palladacyclewas found to be very active in oxidations of secondary alcoholsto the corresponding aldehydes or ketones. The reactions wereperformed with air as the re-oxidant. Therefore, this is anenviromentally friendly oxidation method.Keywords:asymmetric catalysis, chiral ligand,oxazolines, conformational study, allylic substitution,polymer-bound ligands, dendritic ligands, crown ether,oxidations, palladacycle.

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2-(1-Hydroxyalkyl)-6-oxazolyl-and 2-(1-alkoxyalkyl)-6-oxazolylpyridines serve as versatile ligands in the palladium-catalyzed allylic substitution of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. The enantioselectivity of the reaction is dependent on the conformation of the ligands, as deduced by NMR, X-ray crystallography and DFT calculations of palladium(II) complexes of the ligands. The reactions are slow, requiring up to four days reaction time. However, with the use of microwave flash heating, reaction times are reduced to 2 min, with only minor loss in stereoselectivity.

Chiral 2′-(4″,5″-dihydro-2″-oxazolyl)-6′-(1-hydroxyalkyl)pyridines were grafted via ester-linkages directly to cross-linked polystyrene and to polyethyleneglycol-containing resins TentaGel and ArgoGel functionalized with carboxylic acid groups or via spacers containing a carboxylic acid group. The polymeric ligands were used in the palladium-catalyzed substitution of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate. The enantioselectivities (up to 80% ee) were similar to those observed employing an analogous monomeric catalyst.

2-(3‘,4‘-Dihydro-2‘-oxazolyl)-6-(hydroxymethyl)pyridines have been shown by X-ray crystallographic analysis and DFT calculations to exhibit two conformational minima in their complexes with Pd(II) chloride. Theoretical studies of (π-allyl)palladium(II) and (π-olefin)palladium(0) complexes with 2-(3‘,4‘-dihydro-2‘-oxazolyl)-6-(hydroxymethyl)pyridine revealed two minima in each complex. In contrast, in the calculations of the Pd(II) chloride and Pd(II) allyl complexes of 2-(3‘,4‘-dihydro-2‘-oxazolyl)-6-(methoxymethyl)pyridine a single conformational minimum was found. NOE studies of complexes in solution were in agreement with the results obtained by the theoretical studies. The knowledge about the conformational preferences of the palladium complexes with (hydroxyalkyl)pyridinooxazolines and (methoxyalkyl)pyridinooxazolines is used to rationalize the results of palladium-catalyzed allylic alkylations employing the two types of ligands.