Thianthrene radical cations

Thianthrene cation radical tetrafluoroborate 139 has been found to add to 2,3-dimethyl-2-butene 138 at —15 °C to give adduct 2,3-dimethyl-2,3-(5,10-thianthreniumdiyl)butane ditetrafluoroborate 140, which was isolated and characterized by 111 NMR spectroscopy at —15 °C (see Equation 40) <2006JOC3737>. The adduct 140 was stable in CD3CN solution at —15 °C but decomposed quickly at 23 °C, forming the salt of 2,4,4,5,5-pentamethyl-2-oxazoline with loss of thianthrene. 

Benzothiazolylhydrazones 281 react with the thianthrene cation radical to give [l,2,4]triazolo[3,4- ]benzothiazoles 282 in an oxidative intramolecular cylization reaction (Equation 36) <2000BKC425>. 

Tris(aryl)amine and Thianthrene Cation-Radicals... 

The restriction for a nucleophile to penetrate and react with the confined cation-radical sometimes leads to unexpected results. Comparing the reactions of thianthrene cation-radicals, Ran-gappa and Shine (2006) refer to the zeolite situation. When thianthrene is absorbed by zeolites, either by thermal evaporation or from solution, thianthrene cation-radical is formed. The adsorbed cation-radical is stable in zeolite for a very long time. If isooctane (2,2,4-trimethylpentane) was used as a solvent, tert-butylthianthrene was formed in high yield. The authors noted it is apparent that the solvent underwent rupture, but the mechanism of the reaction remains unsolved. ... 

The reaction in Scheme 5.11 gives the snlfoninm salt (anion CIO4 ) in a 90% yield (ronte a). One-electron reduction of the thianthrene cation-radical by anisole is the side reaction (ronte b). Route b leads to products with a 10% total yield. Addition of the dibenzodioxine cation-radical accelerates the reaction 200 times. The cation-radicals of thianthrene and dibenzodioxine are stable. Having been prepared separately, they are introdnced into the reaction as perchlorate salts. 

When the concentration of the thianthrene cation-radical drops from 10 -10 M to 10 M, the reaction results change The sulfonium salt is not produced at all (route a becomes closed) and... 

The formation of the thianthrene cation-radical complex with anisole, that is, (HetH) + ArH (HetH---ArH)+ ... 

Cycloaddition of dimethylbutene (DMB) to the thianthrene cation-radical [(HetH) ] also includes the stage of complexation and oxidation, but in this case the same (HetH)+ is capable of being an additional oxidant (Zhao et al. 2006) ... 

The same way was used by Yoon and Kim (2005) for the preparation of 5-(p-methoxyphenyl)thian threnium ion incorporated in a calyx[4]arene. Namely, the ratio of starting materials, methoxycal-ixarene to the thianthrene cation-radical perchorate, was 1 10. The product of such 5-anisylation of thianthrene was further transformed into a calixarene bearing an additional o-phenylene thio-macrocycle. This macrocylization is beyond the scope of this book the original paper by Yoon and Kim (2005) could be recommended for those who interested in. It is worth noting only one practical importance of the calixarene-phenylene thiomacrocycle here It selectively extracts silver(l-l-) by both calixarene and thiomacrocycle. Each molecule of this combined complexon takes up two silver cations, so that extractability achieves 165%. 

Species 4, produced from thianthrene by loss of an electron from a sulfur, is correctly known as thianthrene radical ion(l+) most authors have referred to it as the thianthrene radical cation or the thianthrene cation radical. The species produced by loss of two electrons from the central ring, and for which 5 is probably a resonance contributor, is termed thianthrenediium. Sulfonium salts (6) produced formally by utilizing a sulfur lone-pair in bonding to, are 5-R-thianthrenium salts. Thianthrene... 

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>. 

This would correspond to an ECEC process at the anode 37 In contrast, the reaction between thianthrene cation radical and water 119- has been shown to occur with the dication as the kinetically active species due to equilibrium (56), corresponding to an electrochemical ECCC process ... 

For the purpose of this review the term heteroaromatic is applied to 7r-radical species when they may be regarded as arising from aromatic heterocyclic molecules or ions by addition or removal of an odd number (usually one) of electrons. Thus, entities such as the anion- and cation-radicals of pyridine (1 and 2) are clearly heteroaromatic. The dilemma whether or not to regard thianthrene (3) as aromatic (its central ring possessing eight electrons) does not arise for the thianthrene cation radical (4) it is heteroaromatic on the grounds that it may formally arise by one-electron reduction of the aromatic thianthrenium dication (5). 

Radical 80 has been prepared as its perchlorate salt by anodic oxidation in ethyl acetate in the presence of hthium perchlorate. The reactivity toward nucleophiles of material so prepared was investigated nitrite and nitrate ions give 2-nitrodibenzo[l,4]dioxin although the mechanisms of the reactions are not clear. Pyridine gives 7V-(2-dibenzo[l,4]dioxinyl)pyridinium ion (84). Other nucleophiles acted as electron donors and largely reduced 80 back to the parent heterocycle they included amines, cyanide ion and water. In an earlier study, the reaction of 80 with water had been examined and the ultimate formation of catechol via dibenzo[l,4]dioxin-2,3-dione was inferred. The cation-radical (80) has been found to accelerate the anisylation of thianthrene cation-radical (Section lII,C,4,b) it has been found to participate in an electrochemiluminescence system with benzo-phenone involving phosphorescence of the latter in a fluid system, and it has been used in a study of relative diffusion coefficients of aromatic cations which shows that it is justified to equate voltammetric potentials for these species with formal thermodynamic redox potentials. The dibenzo[l,4]dioxin semiquinone 85 has been found to result from the alkaline autoxidation of catechol the same species may well be in-... 

Thianthrene cation-radical 178 is one of the most studied of heteroaromatic radicals. Its individual chemistry has proved very rich additionally, it is a persistent, readily recognized radical which has often been used as a well-behaved radical in systems where the prime interest has been the physical chemistry rather than the substrate itself. This chapter cannot deal fully with the chemistry of 178 however, aspects have been reviewed on several and recent occasions. " ... 

The main emphasis of this chapter will be on our attempts to find evidence for radical coupling in reactions of the thianthrene cation radical (Th +) with nucleophiles, that is, for the occurrence of steps such as equations 7 and 8. However, because discussions of reactions of cation radicals with radicals are relatively sparse, we will refer first to other works that principally deal with aromatic nitration. 

The structure of the thianthrene cation radical is shown in structure 1 as Th +. Its electron spin and charge are fully delocalized (2), yet reactions with nucleophiles occur principally at one of the sulfur atoms (3). Therefore,... 

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