Benzo-2,1,3-thiadiazoles

Pesin and his group have continued their investigation of benzo-2,1,3-thiadiazoles and have provided a summary of their recent work. In their opinion, the quinoid structure of benzo-2,1,3-thiadiazole and its selenium analogue is excluded by the sum of their physical and chemical properties, especially i.r. spectra. However, their preferred heteroaromatic structure 

geterotsikl. Soedinenii, 1969, 235 Chem. Abs., 1969, 71, 22 076x). 

Anion radicals of benzo-2,l,3-thia(and selena)diazole have been produced by metal reduction in several solvents at low temperatures, and their electron spin resonance has been studied. The reductive desulphurization of substituted benzo-2,l,3-thiadiazoles by stannous chloride in concentrated hydrochloric acid gives o-phenylenediamines in 80—90% yields. The stability of the heterocyclics against reduction increases with the number of chlorine substituents.  

Nitro-2,l,3-benzothiadiazoles are reduced to the amines by ferrous sulphate in ammonia. Mixtures of 4- and 5-aminobenzo-2,l,3-thiadiazole also arise in the amination of the parent compound (243) with hydroxyl-amine sulphate in concentrated sulphuric acid.  

The oxidative degradation of benzo-2,l,3-thiadiazole by chromic acid produces 4,5-dicarboxy-l,2,5-thiadiazole (250) (up to 78%), which is decarboxylated in nitrobenzene at 160 °C to the 4-monocarboxylic acid (251). The acids give the usual salts and derivatives.  

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C. 1,2,3-Benzothiadiazole 1,1-dioxide. Caution 1,2,3-Benzo-thiadiazole 1,1-dioxide in the solid slate can explode spontaneously, particularly on being warmed, jolted, or scratched. For most purposes it need not be isolated, but can be used in solutions, which are relatively safe. Any operations involving the solid material should be done very carefully, using good shielding. 

An interesting rearrangement was found by Davies and Kirby (1967) in the diazo-tization of 7-amino-benzothiazole (6.68). As Scheme 6-45 shows, the diazonium ion formed initially rearranges under hydrolytic conditions into 7-amino-l,2,3-benzo-thiadiazole (6.69). 

Research on the fluorination of aromatic amines has provided access to 4-fluoro-2,l,3-benzo-thiadiazole (77). Treatment of 4-amino-2,l,3-benzothiadiazole (1) with nitrosonium tetra-fluoroborate (NOBF4), followed by heating of the resulting diazonium salt, gave the aryl fluoride (77) in 23% yield <92SC73>. 

In the presence of alkynes the thieno[3,4-c][l,2,5]thiadiazoles (78) give benzo-thiadiazoles (81) in good yield. These products are formed by desulfurization of the primary adducts (82) (79TL4493, 80JOC2956). Cycloaddition with 6,6-diphenylfulvene has also been reported (80CL1031). 

Benzothiadiazole is oxidized by ozone, potassium permanganate,and chromic acid which all lead to the dicarboxylic acid (8). In the ozonolysis the intermediate crystalline ozonide is decomposed to l,2,5-thiadiazole-3,4-dicarboxaldehyde (isolated as the semicarbazone) as well as 8. Permanganate oxidation has been applied to a number of derivatives of 7, among them being the 5-methyl, 4-nitro, and 4,7-dichloro derivatives. In some cases, particularly in the permanganate oxidation of 4-nitro-2,l,3-benzo-thiadiazole, the yield of 8 is much higher than in the oxidation of the unsuhstituted compound (7). 

Thiete structures have been suggested as fragmentation products in the mass spectra of a thietane fused to a 3-lactam, an ortho disulfide of a thiolbenzoate ester, -propanethiol, thiirane carboxylic acid esters, isothiazoles, thiazoles, 1,3-dithiole 2-thiones, 1,3-dithiolene-2-ones, S-ethyl thio-benzoate, and thianaphthene sulfones. Tetramethylthiete may have been formed on thermolysis of the p-toluenesulfonyl-hydrazone of 2,2,4,4-tetramethyl-3-thietanone. " Thiete 2-thione may be an intermediate in the decomposition of 1,2-ditholium salts by the action of bases. " 2,2-Diphenyl-2H-thiete is suggested as an intermediate in the reaction of diphenyldiazomethane with 1,2,3-benzo-thiadiazole which yields 9-phenylthioxanthene and three other products. ... 

Colella S, Melcarne G, Mazzeo M, Gigli G, Grisorio R, Suranna GP, et al. Synthesis, characterization and photovoltaic properties of random poly(arylene-vinylene)s containing benzo-thiadiazole. Polymer 2011 52(13) 2740-6. 

Bo et al. reported the synthesis of a series of D-A alternating conjugated polymers P24-31 with 5,6-bis(octyloxy)benzothiadiazole as the acceptor unit by Suzuki polyeondensation of dibromo monomers and 5,6-bis(octyloxy)benzo-thiadiazole based diboronic acid pinacol ester. P24) with a of 102 kg mol and a PDI of 1.66, gave a PCE of 5.08% in devices with P24 PC7iBM as the active... 

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