Thianthrene, alkylation

Some 5-(alkyloxy)thianthrenium perchlorates (15) have been prepared in which the alkyl group may be primary or secondary. Reaction with iodide ions may result in 5 n2 reaction at the alkyl group or NAr reaction at the sulfonium sulfur atom leading to the formation of thianthrene. ... 

Electrophilic substitution of thianthrene takes place at C-2. No examples of even minor amounts of 1-mono-substituted product have been reported. Disubstitution gives 2,7- (usually) or 2,8-products. In a few cases, 2,6-derivatives have been claimed. The presence of a sulfoxide or sulfone unit greatly reduces the susceptibility of either ring to electrophilic substitution. Carbon-centered electrophilic addition to sulfur to produce 5-R-thianthrenium salts has been described rarely most examples of the formation of such salts have involved the thianthrene radical ion(l-t-). Treatment of thianthrene with alkyl/aryllithiums produces the 1-lithio-species, and these organometallic derivatives allow the introduction of substituents at this position. 

Mono-2-alkylation of thianthrene with 2-chloropropanoic acid (74GEP2245940) and dialkylation with phenyltrichloromethane/AlCls (81EGP143901) have been claimed in the patent literature. The unusual 2,6-substitution pattern is claimed for chloromethoxymethylation using ClCH20Me/SnCl4(76IZV2799). 

Attempted simple oxidation of alkyl groups on thianthrenes would also effect 5-oxidation. However, sulfones can be side-chain-oxidized 2,3,6,7-tetramethyl-, 1,2,7,8-tetramethyl-, 1,4,6,9-tetramethyl-, and 1,3,7,9-tetra-methylthianthrene tetroxides gave the tetra-acids with 25% HNO3 at 220°C. These tetra-acids were converted to esters and anhydrides in the usual ways (69USP3410868). 

After (presumed). S-alkylation of diphenyl sulfide with Meerwein s reagent, heating the resultant material at 175°C gave a small quantity of thianthrene as a component of a complex product mixture (71JOC1513). 

In Studying asymmetric oxidation of methyl p-tolyl sulfide, employing Ti(OPr-/)4 as catalyst and optically active alkyl hydroperoxides as oxidants, Adam and coworkers collected experimental evidence on the occurrence of the coordination of the sulfoxide to the metal center. Therefore, also in this case the incursion of the nucleophilic oxygen transfer as a mechanism can be invoked. The authors also used thianthrene 5-oxide as a mechanistic probe to prove the nucleophilic character of the oxidant. 

Another aspect of the reactivity of the sulfur atom is illustrated by a reaction done on thianthrene. Indeed, 8 is not sufficiently nucleophilic to be alkylated by methods that work well with dialkyl and alkyl aryl sulfides, although Saeva was able to alkylate it by reaction with -cyanobenzyl bromide and silver triflate <1986T6123>. The sulfonium salt 52 bearing a methyl group can be obtain by an acid-promoted reaction with methyl formate (Equation 4) <1998JCX37522>. 

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>. 

Another method is the use of esters as alkylating agents in triflic acid172 [Eq. (4.44)]. This method has been used to synthesize. S -methylated phenylene sulfide oligomers (methyl triflate, triflic acid, 25°C, 10 h) and to solubilize poly(phenylenesulfide) by transforming it to poly(arylenesulfonium) salts 62 (methyl triflate, methyl or ethyl formate, triflic acid, 110°C, lOh). In a similar way, alkylation of thianthrene to yield the corresponding sulfonium salts (63) has been achieved using alkyl formates.173... 

Polychlorinated Dibenzothiophenes (PCDTs), Thianthrenes (PCTAs) and Their Alkylated Derivatives... 

In competition with this radical coupling reaction is electron transfer between the alkyl radical and thianthrene radical cation. If the radical R- is of sufficiently low oxidation potential (and the reorganization energy permits), e.g., terf-butyl radical, then electron transfer occurs to yield the corresponding cation R+. Evidence for electron-transfer in these reactions was also convincingly demonstrated by the use of unsymmetrical organometallic species. Kochi [29] has shown that the alkyl group that is preferentially cleaved... 

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