2,1,3-Benzoxadiazol

The structure of 1,2,3-benzoxadiazole (4.16) bears some resemblance to Wallis and Dunitz s structure (4.14, Fig. 4-1) for quinoline-8-diazonium-l-oxide, as the latter structure has a tendency towards forming a five-membered heteroaromatic ring. The two compounds are, however, different with respect to the involvement of an N(2) and an N(l) diazo atom. The 1,2,3-benzoxadiazole structure is consistent with the bands observed in the 9.45 to 12.37 eV range in the photoelectron spectrum,... 

Benzotriazoles, see Triazoles 1,2,3-Benzoxadiazole 74f., 136 Benzoxathiete 270 Benzylideneaniline, comparison with... 

Benzoxadiazole 64 is calculated to be 1 kcalmol-1 less stable than its ring open form 61 <2004MI1082> and is mirrored by the 4-nitro 65 and 6-carboxyl 66 substituted analogs that exist exclusively as the ring open isomers 62 and 63 <2000IJQ52> (Section 5.03.3.4). 

The 3-methyl- and 3-phenyl-l,2,3-oxadiazolinium salts 96 and 97 are capable of oxidizing thiols to disulfides <1995MI817>. New dihydro-1,2,3-benzoxadiazoles, prepared by the reaction of 1,2-benzoquinones with diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD) in the presence of triphenylphosphine (Section 5.03.9.4), have been shown to undergo catalytic hydrogenolysis to give phenols (Equation 12) <20050L5139>. 

Table 6 Dihydro-1,2,3-benzoxadiazoles by reaction 3-methoxy-4,6-disubstituted-1,2-benzoquinones (Equation 23) <20050L5139 >...

Other early names of the 1,2-diazonium oxides were based on the benzoxadia-zole cyclised structure. For a long time it was doubted that 1,2,3-Benzoxadiazoles had existence, outside the speculative mathematics of theoretical chemists, but more recent researches suggest photochemical equilibrium with the diazonium form and possible predominance in non-polar solvents. Equilibrium implies similar explosive powers though it is possible that sensitivities differ. 

With a few exceptions simple 1,2,3-oxadiazoles (1) are not isolable because they are less stable than their open tautomers (2) (Equation (1)). The sterically protected 1,2,3-oxadiazole (3) is the only known oxadiazole bearing alkyl substituents. It exists in the cyclic form in the crystalline state but as the diazoketone in chloroform solution <80TH 403-01 >. 1,2,3-Benzoxadiazolehas been detected in a matrix at 15 K <84AG(E)509> this and some substituted 1,2,3-benzoxadiazoles have been shown to exist in equilibrium with their open-chain tautomers <91JST(247)135>. The position of the equilibrium is strongly dependent upon solvent and substituent effects the most stable of the... 

Oxadiazole (1 R = R = H) is calculated to be 8.9 kcal moU less stable than its open chain tautomer (2) (85AG(E)713>. On the other hand, 1,2,3-benzoxadiazole is about 1 kcal mol more stable than 2-diazocyclohexadienone (91JST(247)135>. The position of the equilibrium is markedly affected by substituents. The benzoxadiazole (4) is more stable than its tautomer (5) by about 1.5 kcal mol but tetrafluorobenzoxadiazole is substantially less stable than the corresponding diazocarbonyl isomer. The open-chain forms are also favoured by polar solvents and by hydrogen bonding. In the naphthalene series, the stabilization of the fused oxadiazole (6) relative to its open chain tautomer can be ascribed to partial bond fixation in the naphthalene system, which disfavours... 

In jiingerer Zeit konnte gezeigt werden, dafi 6-Diazo-5-oxo-l,3-cyclohexadien (o-Chinondiazid) in der Gasphase und in unpolaren Solventien im Gleichgewicht mit 1,2,3-Benzoxadiazol vor-liegt8 9 ... 

DINITROBENZENEDIAZOOXIDE or DIAZQDI-NITROPHENOL (Called Dinitrodiazophenol or Dinitro-chinon-diazid in Ger), C6H2N4Og, mw 210.11, N 26.67%, OB to C02 -61.0%. Two isomers are described in the literature 4,6-Dinitrobenzeno-2-diozo-l-oxide or 5,7-Di-nitro-1,2,3-benzoxadiazole, (4,6-Dinitro-2-diazo-phenol or 3,5 Dinitro-l,2-benzoquinone-1-diazide), commonly known as Diozodinitrophenol (DADNPh or DDNP) or Dinol q-... 

We make no comment about benzoisothiazole, ( -X-Y- = -CH=N-, Z = -S-) (XXXVI), 1,2,3-benzoxadiazole (XXXVII), 1,2,3-benzothiadiazole (XXXVIII), or 1,2,3-benzotriazole (XXXIX) ( -X-Y- = -N=N-, Z = -NH-,-0- and -S-) since we lack experimental measurements for the enthalpy of formation of these species in the gas phase and also for their reference species. Estimations can be made for the enthalpy of formation of all of these species, but this seems ill-advised in the current context. 

Unlike 1,2,3-benzoxadiazoles the existence of which is open to question [208-210], 1,2,3-benzothiadiazoles are well known and their nitration has been described in the literature. On nitration of 1,2,3-benzothiadiazoles with sulfuric-nitric mixture Overberger et al. [211] have obtained 4-nitro-l,2,3-benzothiadiazole. 

Nitroderivatives of orf/to-aminophenole on diazotization form the corresponding orf/todiazophenols, which readily undergo cyclization into 1,2,3-benzoxadiazoles (Scheme 2.82) [513-518],... 

The synthesis, structure, and superoxide dismutase mimetic activity in vitro and the protection against reactive oxygen species in vivo of mononuclear copper complexes with 2-(4-methylphenylsulfamoyl)-6-nitrobenzothiazole have been reported [602], Like 1,2,3-benzoxadiazoles, nitroderivatives of 1,2,3-benzothiadiazoles were obtained on diazotization of the corresponding or/Zzo-aminothiophcnolcs [213, 218, 583], The initial or/Zzo-thiophcnols for this reaction were synthesized by nucleophilic substitution of halogen in ort/zo-halogenoanilines. It turned out that 4-nitro- and... 

Benzoxadiazole-l-oxide is obtained by heating o-nitrophenylazide in acetic acid or by oxidation of o-nitroaniline with sodium hypochlorite ... 

Dinitrosobenzene, which was detected spectroscopically, is formed by photoisomerization of 1,2,3-benzoxadiazole-1 -oxide [ 145] ... 

In this interesting reaction, the dihydro compounds 3 are formed from 1,2,3-benzoxadiazole-l-oxide and enamines. y Elimination leads to the products 4. Enolates react in an analogous way [146]. 

Phenazine derivatives result from 1,2,3-benzoxadiazol-1-oxide and phenols Beirut reaction, cf p 196 and [165]) ... 

In basic medium and under mild conditions, phenazine-5,10-dioxides 35 are formed. However, from 1,2,3-benzoxadiazol-l-oxide and enolates or enamines quinoxaline-1,4-dioxides arise. The Beirut reaction possesses considerable preparative scope, but its mechanism has not yet been fully elucidated. 

Reaction of 4,6-disubstituted-3-methoxy-l,2-benzoquinones with dialkyl azodicarboxylates and triphenylphosphine gives dihydro-1,2,3-benzoxadiazoles 99 in good yield (64—94%) (Scheme 25). A multistep mechanism leading to the zwitterionic intermediates 98, which then cyclise to the products 99, has been proposed (05OL5139). An N,N-diphenyl-2,3-dihydro-l,2,3-benzoxadiazole has been obtained (40% yield) by reaction of 3,5-di-f-butyl-l,2-benzoquinone with W-phenyliminophosphorane (PhN - PPhg) (see also Section 3.1.3.2) (02SC2779). 

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