Phenoxathiin cation-radicals

Phenoxanthin, 68 X = S Y = O, is prepared by the electrochemical oxidation of diphenyl ether in dichloromethane and trichloroacetic acid containing tetraethyl-ammonium perchlorate at a composite anode of carbon and sulphur. The anode generates sulphur cations, which carry out electrophilic substitution on the benzene ring [237], Phenoxathiin radical-cation, formed at the potential of the fust oxidation wave, has been characertised by esr spectroscopy [238],... 

Oxidation of CrCl(TPP) in CH2C12 by the radical cation from phenoxathiin hexachloroan-timonate produces a species with (Ueff = 2.8 BM. The electronic spectrum is consistent with Crm(TPP ) or CrIV(TPP) and the former is favoured.1264 An IR band in the 1270 cm-1 region is indicative of a ring-oxidized metalloporphyrin, and there is a strong band at 1285 cm"1 in the spectrum of [CrCl(TPP)][SbCl6].1265... 

Ru (0)2(por " )] (for por = TMP and OEP) have been generated by oxidation of [Ru (0)2-(por)] with phenoxathiin hexachloroantimonate. The products show a broad Q band and a less intense and blue-shifted Soret band, consistent with the formation of the porphyrin cation radical. 

The preparation of a number of 5-(alkyl)thianthrenium perchlorates has been performed from the thianthrene cation radical with dialkylmercurials and tetraalkyltins (R4Sn) <1983JOC143>. Thianthrene as well as phenoxathiin cation radical perchlorates react with alkenes. The former add stereospecifically to cycloalkenes although the latter afforded a mixture of mono- and bis-adducts in which the configuration of the alkene was retained <2003JOC8910>. 

For oxidations, the cation radicals of aromatic compounds like 9,10-diphenyl-antracene, thiantrene, phenoxathiine, or dibenzodioxine are likely candidates. Their reactivity towards nucleophiles, however, limits their application to media of low nucleophilicity. Sometimes the stability of such cation radicals can be enhanced through blocking the reactive positions by substituents. For example, para-substituted triarylamines deliver cation radicals with often excellent stability even in methanol. The stability is further increased by incorporation of urzAu-substituents. Other mediators which have been applied in indirect electrosyntheses are those which are able to abstract hydrogen atoms or hydride atoms. 

The preparation of dibenzo[6,e ][ 1,4]dioxin cation radical (66) has been achieved by oxidation of the heterocycle in ethyl acetate-lithium perchlorate at a platinum anode, using a controlled potential of 1.2 volts vs. Ag-AgC104. The blue solid collected at the anode contained between 85-90% of (66) as the perchlorate (74JHC139). The purple cation radical perchlorate of phenoxathiin, (67), is obtained in high purity by oxidation of phenoxathiin in benzene with 70% perchloric acid-acetic acid (75JOC2756). Similar perchloric acid oxidation of thianthrene affords the dark reddish brown perchlorate of (68) (69JOC3368) and the heterocycle can also be oxidized on a preparative scale with antimony pentachloride (62JCS4963). 

B. Radicals Containing a Six-Membered Heterocycle 1. Phenoxathiin Cation-Radicals... 

The cation-radical 198 of phenoxathiin and its derivatives have been studied in considerable detail. Various workers have measured ESR spectra over several The hyperfine splittings indi-... 

Shine and co-workers have carried out product studies of the reactions of fV-substituted phenothiazine cation-radicals with nucleophilic re-agents. As with the cation-radicals of thianthrene (178) and phenoxathiin (198), addition of certain nucleophiles at S may occur to give, ultimately, such adducts as 270-272 (see Sections III,C,4,b V,B,1). Attack by other nucleophiles may result in reduction by electron transfer or substitution at position 3. Shine has reviewed much of this work. The mechanisms of such reactions have been controversial (see Section... 

Perchloric acid oxidizes perylene (Matsunaga, 1961), thianthrene and phenoxathiin (Murata and Shine, 1969) to the cation radicals, but whether or not the acid serves as the oxidizing agent or catalyses oxidation by atmospheric oxygen has not been studied. 

Because the cyanide ion is so easily oxidized its apparent ability to react with aromatic cation radicals instead of being oxidized by them reflects the competition so often encountered in cation radical chemistry between nucleophilicity and oxidizability of a nucleophile. The subject has not been treated analytically yet. In the present context, the tri-p-anisylaminium ion is reduced by cyanide ion (Papouchado et al., 1969) in a very fast overall second-order reaction (Blount et al., 1970). The cation radicals of thianthrene, pheno-thiazine, and phenoxathiin are also reduced by cyanide ion (Shine et al., 1974). In none of these cases, incidentally, is the fate known of the cyano radical presumed to be formed. Perylene cation radical perchlorate, on the other hand, reacts with cyanide ion in acetonitrile solution to give low (13%) yields of both 1- and 3-cyano-perylene (Shine and Ristagno, 1972). 

Cation radicals of thianthrene (Shine et al., 1972), phenoxathiin, N-methyl- and N-phenylphenothiazine (Shine et al., 1975) react with pyridine as in (138), the pyridinium perchlorates being isolable in... 

Synthesis and Properties.—The two most general methods for preparing sulphonium ylides continue to be a-deprotonation of a sulphonium salt and the reaction of a sulphide (or disulphide with a carbene. A new development involves the reaction of the thianthrene or phenoxathiin cation radical with a dicarbonyl compound, e.g. ethyl benzoylacetate, to give (4). An infrequently used but useful route to sulphonium ylides involves reaction of sulphides e.g. dithia[3,3]cyclophanes with benzyne. A detailed description of a preparation of the sulphonium salt precursor to Trost s diphenylsulphonium cyclopropylide has appeared. The selectivity of ylide formation in the reaction of cyclic and acyclic sulphides with carbenes has been examined and compared with the much... 

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