Longmin Wu

Iron-Catalyzed Stereospecific Olefin Synthesis by Direct Coupling of Alcohols and Alkenes with Alcohols

An efficient Fe(III)-catalyzed direct coupling of alkenes with alcohols and cross-coupling of alcohols with alcohols to give the corresponding substituted (E)-alkenes stereospecifically is demonstrated. Additionally, this reaction could be scaled up. The kinetic isotope effect (KIE) experiments indicated a typical secondary isotope effect in this process. Although benzylic alcohols were effective substrates, mild conditions, atom efficiency, environmental soundness, and stereospecificity are features that make this procedure very attractive.

Synergistic antioxidant effect of green tea polyphenols with α-tocopherol on free radical initiated peroxidation of linoleic acid in micelles

The antioxidant effect of the main polyphenolic components extracted from green tea leaves, i.e., (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCG) and gallic acid (GA), against peroxidation of linoleic acid has been studied in sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) micelles. The peroxidation was initiated thermally by a water-soluble azo initiator 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AMPAD) and the reaction kinetics were followed by formation of linoleic acid hydroperoxides and consumption of the antioxidant. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants in micelles used either alone or in combination with α-tocopherol (vitamin E). The antioxidative action may involve trapping the initiating radicals in the bulk water phase, trapping the propagating lipid peroxyl radicals on the surface of the micelle and regenerating α-tocopherol by reducing α-tocopheroxyl radical. The antioxidant activity of these green tea polyphenols depends significantly on the microenvironment of the reaction medium, the oxidation potential and the size of the molecule.

Kinetic EPR studies on bio-antioxidants

The synergistic antioxidant mechanisms of α-tocopherol (vitamin E) with green tea polyphenols and β-carotene are discussed on the basis of kinetic studies on the reactions of α-tocopheroxyl radical with the green tea polyphenols, β-carotene and retinal by stopped-flow electron paramagnetic resonance technique, and on the inhibition of lipid peroxidation by these antioxidants.

Antioxidant activity of green tea polyphenols against lipid peroxidation initiated by lipid-soluble radicals in micelles

Antioxidant effects of the principal polyphenolic components extracted from green tea leaves, i.e., (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epigallocatechin gallate (EGCG), against peroxidation of linoleic acid have been studied in sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) micelles. The peroxidation was initiated thermally by a lipid-soluble azo initiator di-tert-butyl hyponitrite (DBHN) and the reaction kinetics were followed by formation of linoleic acid hydroperoxides and consumption of the antioxidant. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants in micelles used either alone or in combination with α-tocopherol (vitamin E), but their antioxidative behaviour and relative effectiveness are substantially different from those in the water-soluble initiator AMPAD-initiated peroxidations reported previously. The antioxidative action of the green tea polyphenols (GOHs) in DBHN-initiated peroxidation involves trapping the initiating tert-butoxyl radical and the propagating linoleic acid peroxyl radicals. However, the GOHs could not participate in the α-tocopherol recycling reaction as in the case of AMPAD-initiated reactions due to their very fast reaction with the initiating tert-butoxyl radical.

Novel photoinduced aromatization of Hantzsch 1,4-dihydropyridines

4-Alkyl- and/or aryl-1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylates (Hantzsch 1,4-dihydropyridines) are quantitatively oxidized to the corresponding pyridine derivatives by irradiation in CCl4via a photoinduced electron transfer mechanism.

Kinetic studies on the single electron transfer reaction between 2,2,6,6-tetramethylpiperidine oxoammonium ions and phenothiazines: the application of Marcus theory

Electron transfer reactions take place readily between 2, 2, 6, 6-tetramethylpiperidine oxoammonium ions (la,lb) and phenothiazines (2a—2g), giving corresponding nitroxides (3a,3b) and phenothiazine radical cations (4a—4g). The rate constants for the electron self-exchange reactions between1 and3, as well as between2 and4, are determined by EPR and1HNMR line-broadening effect in acetonitrile. By application of the Marcus theory, the kinetics of the cross exchange reactions between1 and2 is studied.

Effects of resveratrol and its analogs on scavenging hydroxyl radicals: Evaluation by EPR spin trapping method

Resveratrol (3,4′,5-trihydroxy-trans-stilbene) and six analogs, polyhydroxystilbenes, were synthesized. Their effects on scavenging hydroxyl radicals were studied by electron paramagnetic resonance (EPR) spin trapping method. The EPR signal intensity of the spin adduct of hydroxyl radical to 5,5-dimethyl-1-pyrroline N-oxide was detected and used as a standard for the evaluation of the effect of the seven compounds on scavenging hydroxyl radicals. While all seven compounds exhibited hydroxyl radical-scavenging activity, some of them proved to be more effective than resveratrol in this model. Another stable but low-intensity spin adduct was also observed by EPR. A possible assignment is proposed.

Oxidation of Aliphatic α,β-Unsaturated Aldimines to Amides Specifically by Oxone with AlCl3

Abstract α,β-Unsaturated aldimines were specifically oxidized to amides with Oxone in the presence of AlCl3 as a Lewis acid in CH2Cl2. No migration of aryl group occurred in the rearrangement reaction.

14N/15N ISOTOPE EFFECT ON THE ELECTRON TRANSFER PROCESS BETWEEN PHENOTHIAZINE AND ITS RADICAL CATION

An appreciable equilibrium isotope effect has been observed for electron transfer from phenothiazine (PT) to the radical cation of its N-15 substituted analogue ([N-15]PT+.), i,e, PT+[N-15]PT+.K reversible arrow PT+.+[N-15]PT via electron paramagnetic resonance analysis of the mixed radical cations formed from mixing the [N-15]phenothiazlne radical cation hexachloroantimonate and phenothiazine in acetonitrile (K=0.77+/-0.10 at 25 degrees C), and by physical separation of the neutral phenothiazines from the radical cation salts in the equilibrium mixture (K=0.83+/-0.10 at 25 degrees C), Infrared and Raman spectra of [N-14]- and [N-15]phenothiazines and their radical cations were measured to assign the vibrational frequency shifts caused by the heavy-atom substitution and radical cation formation, which gave an estimate of the enthalpy change of 441.7 J mol(-1) for the electron transfer process. These results reveal that N-15 substitution of phenothiazine decreases appreciably the ionization potential of the molecule, making it easier to lose an electron to form the corresponding radical cation in solution

A metal-free catalytic reduction of α,β-unsaturated carbonyl compounds with phenyldimethylsilane

Selective reduction of α,β-unsaturated carbonyl compounds to the corresponding saturated ones by phenyldimethyl silane was promoted by a catalytic amount of I2O5 at ambient temperature in CH2Cl2.