Thianthrene reaction with pyridine

A ring carbon can also be involved, however, as in the reaction of the thianthrene and phenothiazine radical cations in neat pyridine or with pyridine in an anhydrous solvent. In this reaction the 1-pyridinium group is inserted on to the benzo ring (43), apparently via nucleophilic attack on di-cations 42, in turn resulting from oxidation of the initially formed radical cation adducts (Scheme 27). In the presence of moisture the sulfoxides are again formed [84]. 

Condensation of copper salts of acetylenes (240) with o -bromobenzenethiol (239) by slow addition of a pyridine solution of (239) to a dilute pyridine solution of (240) under nitrogen at 110 °C for 24 hours gave the corresponding benzo[6]thiophenes (241) with the following yields R = H, 90% R = Bun or Prn, 80% R = C02Et, 35%. Formation of thianthrene by dimerization of the copper salt of (239) was a competing reaction which became the major pathway in more concentrated solutions. 

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-... 

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