5-Nitro-2,1,3-benzoselenadiazole

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)... 

Reaction of 4-nitro-2,l,3-benzoselenadiazole 143 with ethyl isocyanoacetate in the presence of 1,8-diazabicy-clo[5.4.0]undec-7-ene (DBU) in tetrahydrofuran (THF) at room temperature gave the pyrrole-fused product 146 in 56% yield as the sole product (Scheme 9) <1996J(P1)1403>. Reaction of 5-nitro-2,l,3-benzoselenadiazole 147 with ethyl isocyanoacetate under similar reaction conditions gave the pyridimine iV-oxide-fused product 150 in 28% yield as the sole product. Proposed mechanism for the formation of pyrrole and pyrimidine rings involves initial attack of the ethyl isocyanoacetate anion at the /3-position to the nitro groups forming the anionic intermediates 145 and 148 and the resonance structure intermediate 149. The reactivity and chemoselectivity were explained by the steric effect in the intermediates. 

UV-visible spectra of porphyrin systems obtained on the base 4-nitro-, 4-chloro-7-nitro-2,l,3-benzoxadiazoles or 4-nitro-2,l,3-benzoselenadiazole have been studied in detail [1241],... 

The method of atomic adsorption analysis has been proposed for quantitative determination of mercury in the correspondent salt of 5-nitrotetrazole [1182], Chromatography is widely used for analysis and separation of nitroazoles. For example, thin-layer chromatography was used for separation of nitropyrazoles [1431, 1432], nitroimidazoles [1133, 1309, 1431], nitrobenzoxazole derivatives [1433], and 5-nitro-2,l,3-benzoselenadiazole [1434],... 

The reactions of asymmetrical miinchnone 178a with nitro derivatives of benzofurazan, benzothiadiazole, and benzoselenadiazole gave a mixture of isomeric isoindoles 179 and 180, condensed with the corresponding azoles [136] (Scheme 87). 

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