Benzo oxadiazole 1-oxid

The benzofuroxtin [benzofurazan oxide, 3,4-benzo-l,2,6-oxa-diazole-2-oxide, or 2,1,3-benzoxadiazole-l-oxide (1)] ring system has been reviewed briefly on several occasions, notably by Kaufman and Picard,Boyer, and Behr. The mqst recent of these covers the literature until 1959, and since that date there have been many advances in the subject. This, we feel, justifies the field being covered once more, and its separation from the monocyclic 1,2,5-oxadiazole oxides—the furoxans. We consider also other furoxano-fused compounds in this chapter, subject to the limitation that the ring adjacent to the furoxan is aromatic and six-membered. 

Furoxans and Benzofuroxans (1,2,5-Oxadiazole Oxides and Benzo-1,2,5-Oxadiazole... 

Although benzofuroxan (Bfx) and furoxan (Fx) were first synthesized over 100 years ago, it was not until the middle of the 20th century that its relevant bioactivities were identified. Bfx s and Fx s relevant biological behaviors convert these systems in one of the most current study heterocycles in medicinal chemistry. Formally, these compounds are 1,2,5-oxadiazole hf-oxide derivatives, specifically Bfx should be named as benzo[l,2-c][l,2,5]oxadiazole 1-oxide and Fx as 1,2,5-oxadiazole 2-oxide, however, the common trivial... 

The applications of 1,2,5-oxadiazole iV-oxide and benzo[c][l,2,5]oxadiazole iV-oxide derivatives as compounds which have herbicidal activity are known. For example, the most active compound, butylcarbamoylbenzoL] 1,2,5-oxadiazole iV-oxide, displayed herbicidal activity at concentrations as low as 24 gha-1 <2000JFA2995>. The preparation of 5,7-disubstituted 4,6-dinitrobenzofuroxane derivatives (2-chlorophenylamino, 2,5-dichlorophenyl-amino, 2-hydroxyphenylamino, or 4-bromophenylamino), which are useful as agricultural arachnicides and bactericides, was described <2005RUP2255935>. 

Dioximes of a-diketones such as benzil on oxidation with IBTA are converted into 1,2,5-oxadiazole-A-oxides (furoxans) in high yields (75S445) (Eq. 35). Benzo- (Scheme 46) and pyrido-oxadiazoles (Eq. 36) are formed when o-nitroaniline and 3-amino-2-nitropyridine are subjected to similar oxidation. 

Benzofurazans are thermally more stable but can be cleaved photolytically. For example, benzo-furazan itself in benzene affords cyanoisocyanate (17) and azepine (18), the latter being formed by reaction of the solvent with the putative intermediate acylnitrene (19) (Scheme 5) further supporting evidence for the proposed pathway is provided by trapping the nitrile oxide precursor with dimethyl acetylenedicarboxylate and isolation of the methylurethane derivative of the isocyanate <75JOC2880>. Photolysis of diphenylfurazan yields benzonitrile, diphenylfuroxan and 3,5-diphenyl-1,2,4-oxadiazole. 

Wird ein Benzol-Ring an ein Furoxan anelliert, erhalt man Benzofurazan-l-oxid (Benzofuro-xan, I). Nach Chemical Abstracts wird dieser Heterocyclus als Benzofurazan-1-oxid bezeichnet zudem findet man die Benennungen 3,4-Benzo-l,2,5-oxadiazol-2-oxid, 2,1,3-Benzoxadiazol-1-oxid und 2,1,3-Benzoxadiazol-N-oxid2. 

An examination of the l3C and l5N magnetic resonances of a nitrobenzo[valence tautomerism. The iV-oxide nitrogen resonated at approximately 24 ppm, whereas the other nitrogen atoms resonated in the range —0.2 to 8.6 ppm <90CA(l 12)197462). 

Furazans, i.e. benzo-2,1,3-oxadiazole-A-oxides, undergo isomerism and the rate is influenced by the benzo fusion of another heterocyclic ring <81AHC(29)251>. 

Oxadiazoles," 1,3,4-oxadiazoles" and 1,2,5-oxadiazoles are well known, but the 1,2,3-oxadiazole system, which calculations indicate to be unstable relative to its ring-open diazo-ketone tautomer," is known only as a benzo-fused derivative (in solution) and in mesoionic substances, known as sydnones ," which have been well investigated. Furoxans ," which are formed by the dimerisation of nitrile oxides, have also been extensively studied. 1,2,3-Thiadiazoles, 1,2,4-thiadiazoles, 1,3,4-thiadiazoles" and... 

Oxadiazoles, their A-oxides, as well as their benzo-hised systems, are biologically active compounds. Some of their derivatives are important because of their anthelmintic, fungicidal, bactericidal and herbicidal action. They have also been found to have antitumour activity. 

To a solution of 0.2 g 4-butyl-l-[(benzo[l,2-c]l,2,5-oxadiazol-5(6)-yl-A/ i-oxide) methylidene]semicarbazide (0.72 mmol) and 0.07 mL Et2NH in 0.5 mL DMF, was added 0.13 mL vinyl acetate (1.44 mmol) over 10 min at 0" C. The reaction mixture was then stirred at 40°C for 24 h. An additional 1.3 mL vinyl acetate (14.4 mmol) and 1.0 mL Et2NH were added, and the stirring was continued at 40°C for 48 h. After that, the solvent was removed in vacuo and the oily residue was co-evaporated with toluene (3 x 10 mL). The residue was purified by silica gel column chromatography using CH2CI2 as the eluent to afford 7% 4-butyl-l-[(quinoxalin-6-yl-Ai,A4-dioxide)methylidene] semicarbazide as colorless oil. 

In the mid 1960s, Issidorides and Haddadin addressed some of the limitations in substitution met in earlier reported procedures by developing a synthesis of heteroaromatic A/ oxides that, upon reduction, afford heteroaromatic compounds like phenazine. The Beirut reaction, named after its origin from the capital of Lebanon, involves condensation of benzofurazan oxide (benzo[1,2,5]oxadiazole-1-oxide) and, e.g., enamines, dienes, aldehydes, a,/ -unsaturated ketones, or enolates to form heterocycles... 

The 3 + 2-cycloaddition of A -aryl benzo-fiised sultams (2,3-dihydrobenzoM isothiozole-1,1-dioxides) with benzonitrile oxides in biphasic mixtures formed 5-spiroisoxazoline cycloadducts with complete regioselectivity. The facial selectivity was induced by the A -aryl atfopisomerism. The 1,3-dipolar cycloaddition of nitrite oxides (49) to 4-aryl-2-alkylthio-1 -azetines (50) formed oxadiazabicyclo[3.2. Ojheptenes (51) in 43-72% yields. Thermal cycloreversion of these adducts in toluene produced 5-alkylthio-3-aryl-l,2,4-oxadiazoles (52) in 41-88% yields (Scheme 14). ... 

The introduction of trifluoromethyl groups via copper-catalyzed oxidation under efficient conditions has been reported by Chu and Qing. Moderate-to-excellent yields were obtained and common functionalities such as ester, nitrile, and bromine, were well-tolerated. The reaction works well on heteroarenes and electron-deficient arenes such as 1,3-oxadiazoles and benzo[t/]imidazoles. Selected examples are shown here (Scheme 7.8). 

Among 1,2,5-oxadiazoles, their N-oxides as well as their benzo-fused systems are biologically active compounds which show anthelmintic, fungicidal, bactericidal, herbicidal, and antitumor properties. 

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