2,1,3-Benzothiadiazol

A useful route to 2,1,3-benzothiadiazoles is the F -catalyzed cyclization of l-(4-X-C6F4)-3-trimethylsilyl-l, 3-diaza-2-thiallenes [90JFC(50)359]. Fluoride ion catalysis is also used in the formation of heterocycles from pentafluorobenzoyl and -phenoxy compounds (81BCJ3447). Pentafluoro-phenylcarbonimidoyl dichloride with primary amines gave guanidines,... 

In chlorinations either a substitution or an addition process can occur with the ultimate reaction pathway(s) determined by a combination of factors, which include the reaction conditions, the positions and natures of any substituents present, and the catalyst used. Uncatalyzed chlorination of benzothiadiazole is an exothermic reaction that gives rise to a mixture of isomeric tetrachloro addition products. These are converted in basic medium into 4,7-dichloro-2,1,3-benzothiadiazole (70RCR923). When an iron(III) catalyst is present 4- and 7-chloro substitution becomes the dominant process. Chlorination of a number of 4-substituted 2,1,3-benzothiadiazoles (43) using an oxidative process gave a combination of chlorinated and oxidized products. The 4-hydroxy, 4-amino-, 4-methyl-amino, and 4-acetoxy derivatives of 43 all formed the chloroquinones (44) (40-61% yields). With the 4-aIkoxy substrates both 44 and some 5,7-dichlorinated product were obtained (88CHE96). 

Although derivatives of 2,1,3-benzoxadiazole have been used extensively to make quinoxalines (see Section 1.6.7), the corresponding selena and thia systems have been paid scant attention for that purpose. However, 5-chloro-4-nitro-2,l,3-benzoselenadiazole (456) has been used as a convenient source of 4-chloro-3-nitro-1,2-benzenediamine (457) (HCl + HI, 20°C, 2 h 88%), which was then converted into 6-chloro-5-nitro-2,3(l//,4//)-quinoxalinedione (458) (oxalic acid, 2M HCl, reflux, 2.5 h 23%). ° In addition, irradiation of 2,1,3-benzoselenadiazole (460, X = Se) or 2,1,3-benzothiadiazole (460, X = S) with dimethyl acetylenedicarboxy-late afforded, among other products, dimethyl 2,3-quinoxalinedicarboxylate (459)... 

The numbering systems of mononuclear 1,2,5-thiadiazole 1 and 2,1,3-benzothiadiazole 2 are given below. 2,1,3-Benzothiadiazole, also referred to as benzo[l,2,5]thiadiazole, was often called piazthiole in the early literature. 1,2,5-Thiadiazole was also referred to as 2,5-diazathiophene. Both reduced and oxidized derivatives of 1,2,5-thiadiazole are known. 7... 

The molecular structure of both 1,2,5-thiadiazole 1 and 2,1,3-benzothiadiazole 2 were described in CHEC(1984) <1984CHEC(6)513>. Since the publication of CHEC-II(1996) <1996CHEC-II(4)355>, a large number of single crystal X-ray structures have been published for various monocyclic, fused, and related thiadiazoles. 

In 2-heterosubstituted benzo derivatives (Scheme 51), the effect of the heteroatom X on the ring is similar to the azole series above, and the decreasing scale of aromaticity is 2,1,3-benzoselenadiazole (118)-> 2,1,3-benzothiadiazole (119) > 2,1,3-benzoxadiazole (120).111... 

In Scheme 1.15, path a can be demonstrated with examples of anion-radicals of amino and hydroxy derivatives of 2,1,3-benzothiadiazole (Asfandiarov et al. 1998) and the azafullerene anion-radical, C59HN (Keshavarz et al. 1996). One of the examples, hydrogen atom detachment from C59HN, is as follows ... 

Fig. 4 Chemical structure of a family of PAEs developed independently by the groups of Bunz [57] and Yamamoto [52]. The polymers feature electron-poor 2,1,3-benzothiadiazole and electron-rich 2,5-dialkoxybenzene moieties in an alternating fashion...

The product of the reaction between bis(S-aminodithionitrito)nickel(ii), NH3, HCHO, and MeOH has the structure (179). Complexes of 2,1,3-benzothiadiazole, 2,1,3-benzoselenadiazole, isothiazole, 2-methylbenzo-... 

The C NMR chemical shifts and one-bond coupling constants J( C—H) have been obtained for 2,1,3-benzothiadiazole, 2,1,3-benzoselenadiazole, and 2,1,3-benzooxadiazole in carbon disulfide <74OMR(6)430>. 

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