Styrenes anodic oxidation

In all of the cyclization reactions, Moeller has found only a small difference between the use of alkyl and silyl enol ethers. Since both styrenes and enol ethers have similar oxidation potentials, even the styrene moiety could function as the initiator for oxidative cyclization reactions. The anodic oxidation of simple styrene type precursors leads to low yields of cyclized products so that enol ether moiety seems to be the more efficient initiator for intramolecular anodic coupling reactions [93]. 

Reactions of Ph" radicals (12h) formed at anodes yield styrene (30), biphenyl (31), p-terphenyl (32), insoluble hydrocarbon of high molecular weight and, in smaller amounts, benzene (33) as well as ethanol (19). 30 was the main product for substituted reagents 5q and 5r but for unsubstituted 5e only if the current efficiency, Teu was low. For higher Y i values 31 became the chief organic product. However, in contrast to aliphatic Grignard reagents, except methyl, the current efficiency was always much below 100%. In order to explain the above results the possibility of another route of anodic oxidation, different... 

Anodic oxidation of Grignard reagents (5) in the presence of styrene (30), butadiene (36) or vinyl ethyl ether (37) was investigated by Schafer and Kuntzel as an interesting (for preparative use) extension of other anodic reactions with olefins. The electrolysis was carried out at constant current density at Pt, Cu or graphite electrodes. It was found that the products obtained depend on the electrode material, as is seen from the data presented in Table 9. 

Anodic oxidation of 1,1-diphenylhydrazine in neutral acetonitrile gives a relatively stable diphenyldiazenium ion 39, which may add to styrene in the... 

Moeller has carried out an extensive series of studies of the electrochemical oxidation of electron-rich w-alkenes. One olefinic component is an enol ether, which is converted into an electrophilic center upon oxidation this center then attacks the other site intramolecu-larly. The anodic oxidation of the bis-enol ethers 21 in methanol25 exemplifies the course of such reactions (Scheme 4). The products are w-acetals (22), formed in 50-70% yield in many cases. The cyclization can be used to produce quaternary25 and angularly fused26 bicyclic and tricyclic structures (equation 11). In its original form, this work involved oxidation of a mono-enol ether bearing a nearby styrene-type double bond27. 

There are a few examples of polymers based on vinylbenzofurans. Vinyldibenzofuran 324 has been patented for use in copolymer formulations with other vinyl arenes, used to prepare light-emitting devices <2004USP6803124>. Benzofuran 325 was developed as one of four polymerizable monomers that contain a built-in antioxidant. The polymerization process was transition metal catalyzed <2003MM8346>. Benzofuran 326 also contains the styrene substructure, but there are few examples of its polymerization. Poly(2,3-benzofuran) films were synthesized by anodic oxidation on stainless steel in the presence of boron trifluoride etherate. The films had good thermal stability and conductivity of lO Scm <2005MI1654>. 

The 1,2- and 1,4-addition reactions have been observed also for alkyl-substituted aromatics, but the yields are often low, in particular for benzene derivatives, owing to competing side-chain substitution reactions. Examples include the addition of MeOH to methyl-substituted benzenes [38-42], naphthalenes [43], and anthracenes [43,44]. In a similar fashion, the anodic oxidation of 1,3-dienes in MeOH [45,46] results in mixtures of 1,2- and 1,4-addition products accompanied by substitution products and methoxy-containing dimers and trimers [46]. Styrenes are oxidized in MeOH to the 1,2-addition product together with products formed by dimerization-addition [47,48]. Oxidation of allenes results in most cases in complicated product mixtures resulting from single and double addition reactions [49-52]. 

Anodic oxidation of olefins in the presence of fluoride ions provides mono- and/or difluorinated products [Eqs (2) and (7)] [10,33,34]. Butadiene gives a 1 2 mixture of 1,2-and 1,4-adducts [35]. Anodic fluorination of vinyl sulfides such as 2-(phenylthio)styrene provides vicinal difluorides [36]. 

A remarkable approach was reported in 2004 by Simormeaux and coworkers [53]. Manganese complexes of spirobifluorenyl-substituted porphyrins were elec-tropolymerized by anodic oxidation and the resulting poly(9,9 -spirobifluorene manganese porphyrin) films were shown to be efficient epoxidation catalysts in the presence of imidazole. The polymers were tested in the epoxidation of cyclooctene and styrene using PhIO or PhI(OAc)2 as oxidants. Epoxide yield reached 95% in the case of cyclooctene and 77% in the case of styrene. The electrosynthesized polymers could be recovered by filtration and reused up to eight times without loss of activity and selectivity. 

Iodine is oxidised to iodine(l) at an anode and use has been made of this reagent for the conversion of styrenes to the phenylacetaldehyde dimethyl acetal [66]. Iodine functions as a catalyst in this process. However, a moderate concentration of iodine is required to suppress the direct oxidation of the styrene to give 1,2-dimethoxylated products. 

Table V collects the dimer yields that represent the essential quantity of the preparative data of anodic styrene oxidation. The table also contains the adsorption equilibrium coefficients AT" for styrene obtained by evaluating current voltage curves. Again, the particular physisorptive properties of graphitic carbon for unsaturated molecules are stressed by the data of Table V.

Nishiguchi has shown that electrochemical mediated Mn(OAc)3 oxidation can be used to add acetic acid to styrenes at 95-97 °C under constant current conditions in a beaker-type divided cell with carbon rods as anode and cathode and a ceramic... 

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