1.2.3- Benzothiadiazoles, thermolysis

Unlike simple 1,2,3-thiadiazoles, 1,2,3-benzothiadiazoles do not form thioketenes on thermolysis or photolysis. Instead, they yield many products, depending on the conditions (Equation 3). The mechanisms of these reactions have been extensively studied <1984CB107>. 

Dithiazolyl radical 228 photochemically and thermally disproportionates to afford the 1,2,5-thiadiazole 229 and the unstable 1,2,3-trithiole 230 (Equation 54) <2000JCD3365>. Thermolysis of perfluoro-l,3A4(i2,2,4-benzodithiadia-zine 231 affords complex mixtures of heterocycles including perfluoro-2,l,3-benzothiadiazole 232 and 7,8-difluoro-benzo[l,2- 3,4-f ]bis[l,2,5]thiadiazole 233 (Equation 55) <2005EJI4099>. 

Thermolysis of 1,2,3-benzothiadiazoles (Scheme 10) (IV,D,1) also suffers from this disadvantage, 2 mol equivalents losing two molecules of nitrogen and dimerizing to give a symmetrically substituted thianthrene. 

The thermal and photochemical behavior of benzoselenirene (28) derived from 1,2,3-benzoselenadiazole (27) is very similar to that of benzothiirene (28) generated by the thermolysis or photolysis of the 1,2,3-benzothiadiazole (30) (78JOC2490, 83ZN(B)6li>. Thus, benzothiirene (31) was also found to undergo thermal or photochemical rearrangement to the corresponding 6-ful-venethione (32) (Scheme 3). 

Using similar criteria, the involvement of benzothiirene in the thermolysis and photolysis of 1,2,3-benzothiadiazole was indicated by the isolation of mixed thianthrenes or thiophenols,131 although a report to the contrary has... 

The thioketocarbene 74, generated in the thermolysis of 1,2,3-benzothiadiazole, reacts with carbon disulfide to give the 1 1 cycloadduct 75 and the 2 2 adduct 76 ... 

Benzothiadiazoles.—Further details have been reported of the thermolysis of o-dialkylaminobenzenesulphonyl azides (29) (see Vol. 2, p. 718). The meso-ionic benzothiadiazoles (30) are produced initially, and can be isolated from the dimethylamino-azide (Y = Meg) or when Y is a part of a six-membered ring. In suitable cases, thermolysis of (29) gives (31) directly by a Cope-type elimination of an alkyl group from (30). The azides (29) and the derived benzothiazoles [30 Y = (CHa)6] decompose smoothly in the presence of copper, to afford the fused thiadiazine (32) in 48 and 73% yield, respectively. The azide [29 Y = (CHa) ] gives [31 R = (CHa)5Cl] with 4M-HC1. 

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