Catalysis oxazoline derivatives

Further, Jew and Park successfully applied the efficient phase-transfer catalysis of 32e to the asymmetric synthesis of a-alkyl serines using phenyl oxazoline derivative 55a as a requisite substrate. The reaction is general, and provides a practical access to a variety of optically active a-alkyl serines through acidic hydrolysis, as exemplified in Scheme 4.18 [52]. 

Jew and Park achieved the highly enantioselective synthesis of (2S)-a-(hydroxymethyl)glutamic acid, a potent metabotropic receptor ligand, through the Michael addition of 2-naphthyl oxazoline derivative (55b) to ethyl acrylate under phase-transfer conditions. As shown in Scheme 4.21, the use of Schwe-singer base BEMP at —60 °C with the catalysis of 32e appeared to be essential for attaining an excellent selectivity [60]. 

Monohgated oxazolines derived from commercially available 2-ethyl-2-oxazoUne can form trans-square-planar palladium complexes by simple treatment of this ligand with inorganic palladium salts in methanolic solutions (Scheme 6.15) [72]. The catalysis, when performed in pyrrolidine, gave a yield of 32%, which corresponded to a TON of 190. The Sonogashira reaction was carried out under aerobic conditions with no precautions to exclude moisture from the solvent or substrates. 

It has been found that various sugar oxazoline derivatives serve as monomers for enzymatic catalysis to produce natural and unnatural mucopolysaccharides, in which the monomers were designed and synthesized on the basis of the transition-state analogue substrate (TSAS) concept vide infra).All the sugar oxazoline monomers are of AB-type structure mentioned in Section 4.15.3.2. 

Other chiral grafting species which were linked to mesoporous pure silica phases in order to study chiral catalysis reactions include alkaloids and alkaloid derivates (cinchona and ephedrine ), bis(oxazoline), amino alcohols, proline... 

Planar chiral phosphaferrocene-oxazolines (379) constitute another family of complexes that are usefiil as ligands in asymmetric catalysis. Preparation of these takes advantage of a modified Friedel-Crafts acylation of (373) and an unusual conversion of the resulting trifluoromethyl ketone into an amide that is then cyclized to an oxazoline. The diastereomeric complexes thus formed are chromatographically separable and are used in a palladium-catalyzed asymmetric allylic substitution. Modification of this complex by using the anion derived from 3,4-dimethyl-2-phenylphosphole gives more... 

Chitin was prepared by the catalysis of chitinase. Incubation of a chitobiose oxazoline monomer with chitinase form bacillus sp. in phosphate buffer afforded chitin in quantitative yield (122). Using regiospecific 3-0- and/ or 3 -0-methylated derivatives of a chitobiose oxazoline as new substrate monomers, 3-0-methylated chitin oligomers were produced by enzymatic oligomerization using chitinase (123). 

Yohino, T, Sato, K, Wanme, F, Takai, I, Ishido, Y, Efficient catalysis by pyridinium sulfonate in glycosylation involving an oxazoline intermediate derived from per-O-acetyl-iV-acetyllactosamine and A,V-diacetylchitobiose, Glycoconjugate J., 9, 287-291, 1992. 

Derivatives of oxazolines, pyridines and phosphabicyclic compounds as chiral thioether ligands for asymmetric catalysis 03CCR(242)159. 

Lipase-catalyzed enantiomer-differentiating hydrolysis of racemic phenyl benzyl oxazolin-2-one in aqueous solution in combination with an uncatalyzed in situ racemization of the unchanged enantiomer of the heterocyclic system, with two different lipases, gives access to d- and L-N-benzoyl-phenylalanine 9 and ent-9, respectively. Enantiomer-differentiating alcoholysis and in situ racemization in organic solvents in the presence or absence of added water under the catalysis of lipase can in some cases furnish amino acid derivatives (10-18) with good selectivities and yields. 

The 2-oxazolin-4-one ring is readily opened under mild hydrolytic conditions to yield open-chain amides.127 132 The alkoxy and phenoxy groups in 53 are cleaved rapidly by water in organic solvents, whereas the amino derivative (53, R = NPhj) requires mild acid catalysis. 

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