Oxidative arylation

Sulfoxidations are not restricted to MOs but can also be carried out by dioxygenases. For example. Pseudomonas mutant strain UV4 producing a toluene dioxygenase (TOO) and Pseudomonas NCIMB 8859 expressing a naphthalene dioxygenase (NDO) were used to oxidize aryl sulfides to antipodal chiral sulfoxides [203]. 

Peroxybenzoic acid readily oxidizes aryl and alkyl sulphoxides in acetone, methylene chloride or chloroform solutions, to the sulphone in high yield . The reaction is second order and acid catalysed as is the reaction with peracetic acid . The rate of oxidation is about five times faster than when peracetic acid is used. Other work considering the oxidation of sulphoxides with peracids gathered kinetic evidence and showed that the reaction was indeed second order and that the reaction involved nucleophilic attack by the sulphoxide sulphur atom on the peracid moiety. A further study by the same authors showed that with benzyl and phenyl alkyl sulphoxides the rate of reaction was very sensitive to the inductive effect of the alkyl group. Support for the nucleophilic attack by the sulphur atom on the peracid in acidic solution was forthcoming from other sources . ... 

Scheme 65) <60G1290>. Oxadiazolines (156) are produced by cycloaddition of cyanamides and nitrile oxides aryl (Scheme 66) <66JPR22l>. Thus, for un- and monosubstituted cyanamides, cycloaddition occurs to the C=N double bond of a tautomeric carbodiimide form rather than to a nitrile triple bond. On the other hand, dicyandiamide (157) and benzonitrile oxide furnish (158) (Scheme 67). 

P/A/)-5,6,7,8-Tetrahydrodibenzo ,c)cycloocta-l,3-dienes Oxidative Aryl Coupling with Thallium(lll) Oxidants General Procedures13 ... 

The use of Mn-salen catalysts for asymmetric epoxidation has been reviewed.30 Oxo(salen)manganese(V) complexes, generated by the action of PhIO on the corresponding Mn(III) complexes, have been used to oxidize aryl methyl sulfides to sulfoxides.31 The first example of C—H bond oxidation by a (/i-oxo)mangancsc complex has been reported.32 The rate constants for the abstraction of H from dihydroanthracene correlate roughly with O—H bond strengths. 

Ullrich R, Niiske J, Scheibner K, Spantzel J, Hoffichter M (2004) Novel Haloperoxidase from the Agaric Basidiomycete Agrocybe aegerita Oxidizes Aryl Alcohols and Aldehydes. Appl Environ Microbiol 70 4575... 

Firouzabadi et al. described a solvent-free oxidation of sulfides using stoichiometric amounts of Fe(N03)3 -9H20. This hydrated iron(I II) salt is able to oxidized aryl and alkyl sulfides efficiently at room temperature leading to their corresponding sulfoxides in good yields (92-97%) (Scheme 3.50) [158], The reaction also proceeds in refluxing ethyl acetate however, lower yields of the desired sulfoxides are usually obtained. 

Scheme 2. Oxidative arylation of alkenes by electrophilic palladium (I I).

In a recent review it was argued that such additives of copper, benzoquinone, and HPMOV are not really needed all that is needed is the presence of oxidation-resistant ligands that prevent palladium metal formation [15]. Indeed, activation of the C-H bond is not as slow as, for example, the Wacker reaction of ethene in which reoxidation of palladium must be performed by copper oxidation, although in this catalytic system the additives may still play a role in stabilizing the intermediate low-valent palladium species and thus prevent catalyst decomposition. This thesis was corroborated by the work of de Vos and Jacobs, who showed that addition of benzoic acid to the oxidative arylation reaction in the presence of oxygen led to superior results in the coupling of a variety of substituted arenes with acrylates, cinnamates, and ,/f-unsaturated ketones. Very good yields and TON up to 762 were obtained at 90 °C. A mixture of the o, m, and p isomers is obtained if substituted arenes are used [16]. 

MoCls has a short history as a reagent for the oxidative arylation reaction. It combines strong Lewis-acidic character with high oxidative power. It can, consequently, be successfully employed as the sole reagent in the key step for synthesis of the natural product 41 (Table 3) [14]. Enhancement of the reactivity is achieved... 

Oxidative Arylation Reactions 251 Siegfried R. Waldvogel and Daniela Mirk... 

Anodic treatment of 1,2- or 1,4-dihydroxy-substituted benzenes to form the corresponding quinones or masked congeners is well known, since they represent valuable synthetic intermediates [64]. Benzoquinone ketals of electron rich arenes like 18 can be challenging since the oxidative aryl-aryl coupling reaction usually competes. When using BDD anodes the benzoquinone ketal 19 is obtained in an almost quantitative manner, demonstrating the superior properties of this electrode material. Despite the basic conditions, no deblocking of the silyl-protected phenol moiety is observed [65] (Scheme 9). 

A broad range of biaryl structures, as is often encountered in various classes of naturally occurring compounds, such as alkaloids, lignans, and tannins, can be prepared by oxidative arylic coupling. Oxidative couplings have also been used to build non-natural skeletons, such as the binaphthol derivatives that play an important role in asymmetric synthesis. 

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