Arene oxides reduction reactions

An oxidation-reduction reaction has to be accompanied by a change in the oxidation state of the reactants. Sometimes, these changes aren t that obvious. It helps if you learn how to follow the oxidation states of an element during a chemical reaction. In ionic compounds, it is very obvious where the electrons have been transferred. However, in molecular compounds, electrons are being shared. Oxidation numbers are really fictitious creations that help us better understand atomic behavior. If you remember back to Chapter 6 when we discussed covalent bonds, you may recall that electrons are being shared between atoms in a covalent bond. In many cases, one atom is more electronegative than the other, resulting in a polar... 

Arene Oxides-Oxepins 4. Oxidation-Reduction Reactions... 

Oxidation-reduction reactions which lead to a change in the oxidation state of the metal are the most typical for sandwich arene complexes. However, this is not true for... 

The reversible oxidation-reduction reaction Ar2Cr Ar2Cr" is characteristic of bis arene x-complexes of chromium. This property of chromium... 

A clever application of this reaction has recently been carried out to achieve a high yield synthesis of arene oxides and other dihydroaromatic, as well as aromatic, compounds. Fused-ring /3-lactones, such as 1-substituted 5-bromo-7-oxabicyclo[4.2.0]oct-2-en-8-ones (32) can be readily prepared by bromolactonization of 1,4-dihydrobenzoic acids (obtainable by Birch reduction of benzoic acids) (75JOC2843). After suitable transformation of substituents, mild heating of the lactone results in decarboxylation and formation of aromatic derivatives which would often be difficult to make otherwise. An example is the synthesis of the arene oxide (33) shown (78JA352, 78JA353). 

New nickel-benzyne complexes (143-147) have been prepared by reaction of o-dihaloarenes with Ni(COD)2 in the presence of a trialkylphosphine followed by reduction of the oxidative addition product with either Li or 1% Na/Hg in ether [e.g., Eq. (23)]. The oxidative addition reaction depends on the nature of substituents on the arene and fails to occur when strong electron-donating groups are present. Based on NMR and mass spectrometry (MS) data, the new complexes were formulated as monomeric. It had been... 

The lactam derivative dibenz[h/]l 4-oxazepin-ll-(lOH)-one is a primary metabolic product of metabolism and a direct precursor of the urinary hydroxylated metabolites. In rats, the lactam, a dihydro-CR metabolite, an amino alcohol of CR, and an arene oxide are metabolites in CR degradation. In the rat, the major mechanism for elimination is sulfate conjugation and biliary excretion to a limited extent. Phase I metabolism by microsomal mixed fimction oxidases involves reduction of CR to the amino alcohol, oxidation to form the lactam ring, and hydroxylation to form the hydroxylactams. Phase II conjugation reactions sulfate the hydroxylactam intermediates for renal elimination. Amino alcohol intermediates are conjugated with glucuro-nide for biliary secretion. 

Arene oxides show the characteristic reactions of epoxides (isomerization to ketones, reductions to alcohols, nucleophilic additions, deoxygenations) and olefins or conjugated dienes (catalytic hydrogenation, photochemical isomerization, cycloaddition, epoxidation, metal complexation). Where a spontaneous, rapid equilibration between the arene oxide and oxepin forms exists, reactivity typical of a conjugated triene is also found. 

The earliest reduction reactions of arene oxides to be reported involved catalytic hydrogenation of 1 (H2-Pd) to yield oxepane and reaction with lithium aluminium hydride to give cyclohexa-l,3-dien-5-ol. An alternative type of reduction reaction... 

Dr. Fred Guengerich at Vanderbilt University has published mechanistic schemata for cytochrome P450 involvement in an extensive array of both common and uncommon oxidative reactions and reductive reactions. Some of those are exhibited later in this chapter in a brief consideration of reductive reactions. Mechanisms for carbon hydroxylation, heteroatom oxygenation, N-dealkylation, O-dealkylation, alcohol oxidation, arene epoxidation, phenol formation, oxidation of olefins and acetylenes, reduction of nitro compounds, reductive dehalogenation, and azo reduction, to name a few, are provided. 

The precipitation of [V(CO) Arene] [V(CO)g] in the reaction medium is probably preceded by the formation of a soluble substitution product of V(CO)g. In view of the known (1,6) oxydising properties of hexacarbonylvanadium, the formation of the final ionic compounds clearly involves an oxidation-reduction step by a second molecule of V(CO)g. The nature of the intermediate substitution product will be discussed. 

Reactions involving electrophilic substitution of hydrogen in arenes are known for both nontransition [Hg(II), Tl(III), Pb(IV)] and transition metals [Au(III), Pd(II), Pt(IV)] [49]. Pd(II)-catalyzed acetoxylation involves arene activation via formation of an organometallic aryl-Pd c-complex followed by oxidative addition of oxidant and reductive elimination to restore Pd(II) and release the product [11, 50]. Without oxidant, coupling reactions predominate, suggesting arylpalladium(IV) and arylpalladium(II) intermediates in the routes leading to aryl acetates and biaryls, respectively (Scheme 14.10). 

The reductive elimination from metal-alkyl-hydride complexes L MR(H) (M = Ir, R = Cy or M = Rh, R = Ph) giving the alkane or arene occurs with inverse kinetic isotope effects which were taken into account by a preequilibrium with the a-alkane or r -arene complex. These reactions represent the microscopic reverse of oxidative addition of an alkane or arene C-Fl bond on electron-rich 16-electron metal centers... 

Scheme 19.7 Synthesis of (a) mono- or (b) di- and (c) per-hydroxylated pillar[S]arenes using deprotection strategies using BBrs and sequential oxidation and reduction reactions, respectively...

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