Oxygen reaction with arenes

More recently, Curran and Keller found that the (TMSlsSiH-mediated addition of aryl iodides to arenes are facilitated by oxidative rearomatization with oxygen (Reaction 69). Here, AIBN is not necessary for good performance of the reaction. The reaction proceeds well in both inter- and intra-molecular (see above) versions. 

Productive bimolecular reactions of the ion radicals in the contact ion pair can effectively compete with the back electron transfer if either the cation radical or the anion radical undergoes a rapid reaction with an additive that is present during electron-transfer activation. For example, the [D, A] complex of an arene donor with nitrosonium cation exists in the equilibrium with a low steady-state concentration of the radical pair, which persists indefinitely. However, the introduction of oxygen rapidly oxidizes even small amounts of nitric oxide to compete with back electron transfer and thus successfully effects aromatic nitration80 (Scheme 16). 

Methyl benzoate, anisole, and diphenyl ether each give sandwich compounds with chromium vapor, although in rather low yield (32, 55, 110). Chromium appears to attack alkyl ethers and this deoxygenation probably competes with complexation with the aromatic oxygen compounds. No simple product has been isolated from chromium atoms and aniline, but bis(7V,7V-dimethylaniline)chromium has been prepared (32). The behavior of molybdenum and tungsten vapors closely resembles that of chromium in reactions with oxygen- and nitrogen-substituted arenes (113). 

Singlet oxygen reacts with binaphthylphosphine derivatives such as 1, l -binaphthyldi-/-butylphosphine to form the corresponding binaphthyl-2-oxide phosphine oxides. This intramolecular arene epoxidation reaction proceeds with complete retention of stereochemistry. The binaphthyl-2-oxide di-/-butylphosphine oxide undergoes a slow NIH rearrangement to form the corresponding hydroxylated product. A transient phospha-dioxirane intermediate has been directly observed by low-temperature NMR.241... 

As hosts for cations, the phenolic oxygen atoms at the calixarene lower rim (Figure 3.81) have the potential to act in a similar way to the anisole residues of the spherands, either in the original hydroxyl form or as alkyl ether derivatives. This kind of behaviour has been observed for the methyl ether of the parent /j-f-butylcalix[4] arene (compound 3.121) upon reaction with a mixture of sodium benzoate, one... 

Figure 7 Formation of side-on peroxo intermediate [CujlR-XYL) (02 )] (5 ) from O2-reaction with [Cu (R-XYL)], followed by oxygenation of the arene bridge...

Facile arene displacement is favored by hard donor solvents (T), particularly oxygenated ones like acetone, THF, and water. Reaction with MeCN shows second-order kinetics with activation parameters consistent with a SN2 mechanism where the MeCN adds directly to the metal. This reaction is 104 times faster for Re than for the Mn analog, due to the larger size of Re, thus explaining why preparations employing hydrolytic work-up work well for Mn but not for Re. 

In general, nucleophilic addition reactions of arene oxides with nonpolarizable oxygen and nitrogen nucleophiles are very slow. Thus both NH3 and NHj nucleophiles failed to add to benzene oxides under a range of conditions. Amine nucleophiles have, however, been found to react very slowly with benzene oxide. 

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