Arene derivatives oxidation reactions

Nitration of arenes. Reaction of 1-naphthol with CAN in acetic acid results in 2,4- and 4,6-dinitro derivatives. The reaction with CAN absorbed on silica gel results in 2-nitro- and 4-nitro-l-naphthol in 42 and 38% yield, respectively. Polynuclear arenes are not oxidized to quinones by CAN supported on silica but are converted mainly into mononitro derivatives. Thus phenanthrene is converted into 2-nitrophenanthrene (45% yield) and 3-nitrophenanthrene (28% yield).1... 

The ratio of parallel reactions of O3 with the aromatic ring versus substituents of toluene and its derivatives in acetic anhydride depends on the arene structure and reaction conditions. Tri- and tetra-methylbenzenes were oxidized only at the benzene... 

The intermolecular oxidative arylation of olefins has been reported in most cases with acrylic acid derivatives. This process could be developed as an alternative to the Heck reaction, which occurs with aryl halides. Several groups have reported versions of this oxidative C-C bond formation. Fujiwara reported intermolecular examples of this reaction catalyzed by palladium and copper (Equation 18.64). Intermolecular versions of this reaction have also been reported with ruthenium catalysts and as the oxidant. Other oxidative reactions in which electron-rich arenes add to olefins (Equation 18.66) have been reported as stoidiiometric steps of natural products syntheses, and later as a catalytic process. ... 

The authors also investigated the C—H borylation of a series of substituted pyridine 332-333 and arene 334-336 derivatives. Careful examination of the reaction conditions revealed that high yields could be obtained in the presence of 3 mol% catalyst and the diborane B2Pin2 (HBPin is formed in situ) in 0.55 M THE In these cases, THF was favored over running the reaction neat since the pyridine and arene derivatives were often solids. Through their studies the authors determined that borylation occurred at the most sterically accessible C—H bonds, with the selectivity arising from the C—H oxidative addition step. In addition, electron-poor arenes borylated much more readily than the electron-rich examples due to the acidity of the C—H bond. 

Nevertheless, the application of alkoxy-functionalized 1,3-dienes is of increasing interest. 1-Alkoxy-functionalized 1,3-butadienes led directly to arene derivatives such as 22 via the cycloaddition/elimination route (Scheme 13.12) [13]. The arene is formed under the reaction conditions of cobalt catalysis upon elimination of trimethyl-silanol from the labile dihydroaromatic intermediate. When 2-alkoxy-functionalized 1,3-butadienes are employed, 3,4-disubstituted phenol derivatives such as 23 are readily available by DDQ oxidation of the dihydroaromatic intermediate. The DDQ oxidation conditions led in several cases to direct desilylation of the enol ether or the desilylation takes place during column chromatography on (nondeactivated) silica gel. 

The Fujiwara-Moritani reaction enables the coupling of alkenes with arenes under oxidative conditions—also named oxidative Heck reaction (for the mechanism, see Ref [ 29]) Garcia-Rubia et al. used this Pd"-catalyzed oxidative direct C-H alkenylation to produce /rans-stilbene derivatives.As exemplified by their synthesis of pterostilene (Scheme 5-45), a partially methylated resveratrol derivative, a 2-pyridyl sulfinyl group efficiently promotes the Pd"-catalyzed ortho C-H olefination of arenes and can be readily removed or transformed into a thiol group. 

In equation 1, the Grignard reagent, C H MgBr, plays a dual role as reducing agent and the source of the arene compound (see Grignard reaction). The Cr(CO)g is recovered from an apparent phenyl chromium intermediate by the addition of water (19,20). Other routes to chromium hexacarbonyl are possible, and an excellent summary of chromium carbonyl and derivatives can be found in reference 2. The only access to the less stable Cr(—II) and Cr(—I) oxidation states is by reduction of Cr(CO)g. 

Numerous reactions have been described in which the oxygen of the oxepin system is removed to give benzene derivatives. The formation of the aromatic products can be rationalized by an arene oxide as intermediate. A suitable reagent for the elimination of an oxygen atom from this heterocycle is triphenylphosphane, e.g. formation of l,24 2a,12 and 2b.1,9... 

---