Bis Oxazoline Research Articles

Catalytic Asymmetric Friedel-Crafts Alkylation of β,γ-Unsaturated α-Ketoesters: Enantioselective Addition of Aromatic C-H Bonds to Alkenes.

Useful catalytic BOXes: Chiral bisoxazoline (BOX)/Lewis acid complexes can catalyze highly enantioselective Friedel–Crafts alkylation reactions. The new reaction (see scheme) is successful with both aromatic and heteroaromatic compounds and with a wide range of β,γ-unsaturated α-ketoesters (R1 = alkyl, aryl, or a protected alcohol). Products are formed with up to >99 % ee.

Characterization by epr spectroscopy of the chiral catalysts bis(oxazoline)-Cu supported in laponites

Se presenta un estudio mediante Resonancia Paramagnetica Electronica del complejo quiral Bis(oxazolina)-Cu(II) soportado en laponita (hectorita sintetica) (libre de hierro. Del mismo se concluye que el complejo se incorpora en el espacio interlamelar de la arcilla dando lugar a entidades de Cu(II) aisladas en las cuales el metal se coordina a atomos de oxigenos y nitrogenos con una simetria practicamente planocuadrada, independientemente del disolvente empleado. Ello indica, de acuerdo con los datos previos de espectroscopia de absorcion de rayos-X, que los ligandos cloruro del complejo son intercambiados en el proceso de incorporacion de forma que los oxigenos de la superficie interlaminar y externa de la arcilla actuan como contraiones.

IMPROVEMENT OF COMPATIBILITY IN GLASS-REINFORCED PA6/PP BLENDS

This article deals with the study of the properties of glass-reinforced (30% in weight) compatibilized blends of polypropylene (PP) and polyamide (PA6). Reological properties (melt flow index and melt stability) and mechanical properties (tensile strength, flexural strength, and impact) of PA6/PP blends were investigated. The influence of potential compatibilizators 4,4′-diphenylmethane carbodiimide (OCDI), 4,4′-diphenylmethane bismaleimide (BMI), and 2,2′-(1,4-phenylene)-bisoxazoline (BOX) on mechanical properties and thermostability of initial and glass-reinforced polymer blends was investigated too. We tried to study the structure of glass-reinforced composites by mercury-intrusion porosimetry. The influence of compatibilizators on the molecular weight of PA6 was studied by gel permeation chromatography; that on the chemical structure of blends was investigated by nuclear magnetic resonance and infrared spectroscopy. The addition of OCDI and BOX (chain extenders) preserves the product formation as they react with the active and carbonyl groups of PA6. BMI has lower reactivity. Grafting of BMI to PP chains improves compatibility in the PA6/PP blend and increases PP adhesion to glass fiber.

Enantioselective cyclopropanation reactions promoted by immobilized bis(oxazoline)–copper complexes

Bis(oxazoline)–copper complexes can be immobilized by cationic exchange or a covalent bond to the support. In the first strategy the co-ordination properties of the solid counterion influence the results obtained, as is the case in the homogeneous phase. However, the solid counterions also lead to steric interactions with the chiral ligand and so the bis(oxazoline) behaves differently depending on its substituents and the nature of the anionic support. The best overall results are obtained with nanocomposite Nafion–silica as a support and the bis(oxazoline) with phenyl groups. In the second strategy the covalent bond between the ligand and an organic support can be achieved using a preformed polymer or by synthesis of the support using a functionalized chiral ligand. The best results are obtained with the latter system but the copolymerization conditions are critical for the activity and enantioselectivity of the catalyst.

Chiral Bis(oxazoline)-copper Catalyzed Enantioselective Imidation of Sulfides

Prochiral sulfides reacted with Phl=NTs in the presence of a catalytic amount of Cu(I) salt together with a chiral 4,4′-disubstituted bis(oxazoline) ligand to afford the corresponding chiral sulfimides.