Arenes anisoles oxidation

Early examples of electron transfer processes are shown in equations (2), (12), and (13). Birch in 1944 followed up the findings of Wooster, and demonstrated that Na metal and ethanol in ammonia reduce benzene, anisole, and other aromatics to 1,4-cyclohexadienes. Birch speculated about the mechanism of this reaction, but did not explicitly describe a radical pathway involving 55 (equation 87) until later, as described in his autobiography. Electron transfer from arenes was found by Weiss in 1941, who obtained crystalline salts of Ci4H]o from oxidation of anthracene. ... 

The oxidative carbonylation of arenes to aromatic acids is a useful reaction which can be performed in the presence of Wacker-type palladium catalysts (equation 176). The stoichiometric reaction of Pd(OAc)2 with various aromatic compounds such as benzene, toluene or anisole at 100 °C in the presence of CO gives aromatic acids in low to fair yields.446 This reaction is thought to proceed via CO insertion between a palladium-carbon (arene) allyl chloride, but substantial amounts of phenol and coupling by-products are formed.447... 

Organosulfur compounds are especially useful for C-fluorine bond forming reactions with (difluoroiodo)arenes. For example, dithioketal derivatives of benzophenones are readily converted to diaryldifluoromethanes with two equivalents of DFIT in dichloromethane [105]. This transformation has also been effected with electro chemically prepared p-(difluoroiodo)anisole/Et3N 3HF, and by anodic oxidations of p-iodoanisole in acetonitrile solutions containing Et3N 3HF and dithioketal substrates (Scheme 35) [96]. Under the latter conditions, p-(difluoroiodo)anisole is continuously regenerated, and the iodoarene was employed at catalytic levels for high yield conversions of the dithioketals to diaryldifluoromethanes. 

The known vanadium carbonyl cations are of two types, namely a tetracarbonyl, [AreneV(CO)4]+, and a dicarbonyl, [Cp2V(CO)2]+. The tetracarbonyl derivatives are readily prepared under mild conditions by the reaction of an arene with vanadium hexacarbonyl. The arenes used include benzene, its methyl derivatives 28, 29), naphthalene, and anisole 29). The cation is probably formed by oxidation of the intermediary arene vanadium tricarbonyl. 

One of the first eye-catching synthetic applications of arene-chromium chemistry was the synthesis of the sp/ro-sesquiterpenes ( )-acorenone and ( )-acorenone B (rac-7) disclosed by Semmelhack and Yamashita in 1980 [14]. These authors twice exploited the meta-selective nucleophile addition to anisole-Cr(CO)3 derivatives (Scheme 1). Starting from complex rac-1, such a reaction is first used for the regioselective introduction of an acyl sidechain to give 2 after oxidative workup. A few steps later, the nitrile rac-4 (obtained from rac-3 by complexation and separation of the diastereomeric products by preparative HPLC) is deprotonated to form the spiro addition product rac-5, from which the enone rac-6 is obtained after protonation and hydrolysis of the initially formed dienol ether. The final conversion of rac-6 into acorenone B (rac-7) efficiently proceeds over five steps and involves a diastereoselective hydrogenation of an exo-methylene group. 

The use of 7r-arene-Cr(CO)3 complexes in organic synthesis continues to attract attention. Carbanion attack on 7r-anisole- and 7r-toluene-chromium tricarbonyl complexes gives, after oxidative work-up, meta-substituted aromatics as the major product [equation (24)]. With the anisole complex the me/a-substituted product... 

In 1980 Fujiwara and colleagues described for the first time a palladium-mediated oxidative carbonylation of arenes to benzoic acids [9—11]. The direct carboxylations of benzene, toluene, anisole, chlorobenzene, furan, and thiophene were carried out under CO and in the presence of Pd(OAc)2- 2-43 % of the corresponding benzoic acids were formed as the terminal products. Later on, the reaction was performed with a catalytic amount of palladium salts using tert-... 

With Ruthenium In 2001, Milstein s group [74] reported the first nondirected oxidative arylation of olefins using Ru catalysts. In this approach, a series of arenes (in excess), which included chlorobenzene, toluene, anisole, and />-xylene, were treated with RUCI3-3H2O (0.4mol% ) and either methyl acrylate, ethene, or CH2=CH(CF2)3CF3 in the presence of both CO and oxygen and heated in a sealed vessel to 180 °C for 48 h. The yields were only moderate, and turnover numbers (TONs) of 5.4—118 could be obtained. The active catalyst was considered to be an electrophilic Ru carbonyl species. 

DeBoef and co-workers described the aerobic oxidative inter- and intra-molecular coupling of benzoxazole (120) with benzene derivatives in the presence of catalytic amounts of Pd(OAc)2 and heteropolymolybdovanadic acid (HPMV) (Scheme 10.40). Under these conditions, the monoarylated C2 products 121-123 were obtained in moderate to good yields in less than 2 hours extended reaction times led to formation of the undesired 2,3-diarylated products. Problematic coupling partners included anisole (which afforded regiomeric mixtures of the C2 product) and electron-poor or acidic arenes which led to no product formation. Palladation is thought to occur at the more nucleophilic C3 position before migration to the C2 position and biaryl product formation. 

The extensive studies on the migration and retention of deuterium or tritium in aromatic substrates which have been carried out indicate that the magnitude of the retention is considerably influenced by the nature of substituents in the aromatic ring. Several inconsistencies which have been observed are only adequately resolved by assuming that decomposition of the arene oxide (Figure 4.13) can take place by both pathways a and b Thus in some cases such as chlorobenzene and anisole (61 and 62) hydroxylation gives the 4-hydroxy derivatives but the retention of deuterium in this product is dependent on whether the deuterium was initially present at the position of substitution or in the adjacent position. In these cases deuterium is preferentially retained when it is originally present in the substrate in the adjacent position to substitution (62) , and it must be assumed that both pathways a and 6 are operative in the decomposition of the intermediate arene oxides. 

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