4- Amino-1,2,5-oxadiazole 2-oxides

R CONHNHCOR (ii) the formation of oxadiazoles by oxidation of acylhydrazones RCH=NNHCOR, and (iii) the formation of oxadiazolinones, oxadiazolinethiones, and amino-oxadiazoles by the action on hydrazides RCONHNH2 of phosgene, carbon disulfide (or thiophos-gene), and cyanogen bromide respectively. 

Although not particularly well known, nitrosoimidazoles appear to be quite stable compounds. The nitroso function can be reduced to amino, or oxidized to nitro. When 5-nitroso-2,4-diphenylimidazole is subjected to dropwise treatment with phenylhydrazine there is some reduction, but ring modification with the formation of the oxadiazole (224) accompanies this reaction (Scheme 123) (60G831). The nitroso function is able to take part in condensation reactions with compounds which possess active methylene groups, and related species (B-76MI40701). 

Oxadiazoles. Mesitonitrile oxide adds j A -dicyanomethylamine, MeN-(CN)2, to yield the oxadiazole (471 Ar = 2,4,6-Me3C6H2). The action of hydroxylamine on the cyanoimino-ether ArCH2C(OEt)=NCN (Ar = 2,6-CI2C6H3) unexpectedly leads to the 3-amino-oxadiazole (472). 3-Azido-... 

Other non-traditional preparations of 1,2,3-triazoles have been reported. The rearrangement in dioxane/water of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole into (2-aryl-5-phenyl-27/-l,2,3-triazol-4-yl)ureas was investigated mechanistically in terms of substituents on different pathways <06JOC5616>. A general and efficient method for the preparation of 2,4-diary 1-1,2,3-triazoles 140 from a-hydroxyacetophenones 139 and arylhydrazines is reported <06SC2461>. 5-Alkylamino-] //-], 2,3-triazoles were obtained by base-mediated cleavage of cycloadducts of azides to cyclic ketene acetals <06S1943>. Oxidation of N-... 

The base and acid hydrolysis of. syrw-triazine mononitriles has been studied <06CHE642>. The potassium salt of 2-amino-4-methoxy-6-dinitromethyl-l,3,5-triazines 30 with N204 afforded the nitroformaldoximes 31 and the 1,2,5-oxadiazole iV-oxides 32 <06CHE1096> <06CHE557>. 

The thermally induced rearrangements in the furoxan series have also been found. In particular, the transformation of 3-R-substituted 4-(3-ethoxycarbonylthioureido)-l,2,5-oxadiazole 2-oxides into derivatives of 5-amino-3-(a-nitroalkyl)-l,2,4-thiadiazole and into (5-amino-l,2,4-thiadiazol-3-yl)nitroformaldehyde arylhydrazones has been reported (Equation 8) <2003MC188>. 

Diazotization of 4-amino-l,2,5-oxadiazole-3-carbohydroximoyl chloride 132 gives 4-[chloro(hydroxyimino)-methyl]-l,2,5-oxadiazole-3-diazonium salt 133 (Scheme 35). Treatment of the latter with NaN3 afforded 4-azido-l,2,5-oxadiazole-3-carbohydroximoyl chloride 134 and the reaction with NaN02 yielded 2-cyano-2-hydro-xyiminoaceto-hydroximoyl chloride 135. By oxidation of 4-amino-l,2,5-oxadiazole-3-carbohydroximoyl azide 136... 

Dimerization of nitrile oxides derived from 4-amino- and 4-R-substituted l,2,5-oxadiazole-3-carbohydroximoyl chlorides 201 leads to the formation of tricyclic furoxans 200 or compound 202 (Scheme 45) <2001RJ01355>. 

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>. 

Electrophilic substitution of the ring hydrogen atom in 1,3,4-oxadiazoles is uncommon. In contrast, several reactions of electrophiles with C-linked substituents of 1,3,4-oxadiazole have been reported. 2,5-Diaryl-l,3,4-oxadiazoles are bromi-nated and nitrated on aryl substituents. Oxidation of 2,5-ditolyl-l,3,4-oxadiazole afforded the corresponding dialdehydes or dicarboxylic acids. 2-Methyl-5-phenyl-l,3,4-oxadiazole treated with butyllithium and then with isoamyl nitrite yielded the oxime of 5-phenyl-l,3,4-oxadiazol-2-carbaldehyde. 2-Chloromethyl-5-phenyl-l,3,4-oxadiazole under the action of sulfur and methyl iodide followed by amines affords the respective thioamides. 2-Chloromethyl-5-methyl-l,3,4-oxadia-zole and triethyl phosphite gave a product, which underwent a Wittig reation with aromatic aldehydes to form alkenes. Alkyl l,3,4-oxadiazole-2-carboxylates undergo typical reactions with ammonia, amines, and hydrazines to afford amides or hydrazides. It has been shown that 5-amino-l,3,4-oxadiazole-2-carboxylic acids and their esters decarboxylate. 

Dipolar cycloaddition of nitrile oxide at the C=N bond of indole imino esters 130, followed by elimination of the alcohol moity gives oxadiazole derivatives 131 (Scheme 1.26) (298). Reaction of N-arylbenzamidines with arenenitrile N-oxides (generated in situ from oximoyl chlorides) produce unstable 5-amino-4,5-dihydro-1,2,4-oxadiazoles which, on aqueous acidic treatment hydrolyze to open-chain N-benzoyloxy-N -arylareneamidines (299). 

Bipolar Molecular Glasses. Recently, bipolar molecular glasses have been described that allow both injection of holes and electrons (Fig. 3.30). 2- 4-[bis(4-methylphenyl)amino]phenyl -5-(dimesitylboryl)thiophene (PhAMB-lT, 68) and 2- 4-[bis(9,9-dimethylfluorenyl)amino]phenyl -5-(dimesitylboryl)thiophene (F1AMB-1T, 69) show oxidation potentials of 0.62 and 0.58 V, and reduction potentials of —2.13 and —2.01 V vs. Ag/0.01 Ag+, respectively [145]. Oxidation as well as reduction leads to stable radical ions. With the conversion rules given above, the HOMO and LUMO levels can be estimated to be approximately at —5.3 and —2.8 eV. In comparison, for the bipolar compound 70, consisting of triarylamine and oxadiazole moieties, the values are —5.5 and — 2.7eV [129]. However, in this case no data on the stability of the radical ions are available. 

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. 

Bei der Einwirkung von Phosgcn auf 2-Amino-pyridin-N-oxid erfolgt glatte Cyelisierung ohne Isolierung einer Zwischenstufe unter Bildung von 2-Oxo-2II-yrido[l,2-b]-],2,4-oxadiazol (Schmp. 185-1870)84 ... 

Das durch Pcriodat-Oxidation von 0-Acetoxy-N-(l-amino-ethyliden)-hydroxylaminen erhsilt-liche 1-Hydroximino-l-nitroso-ethan setzt sich mit Benzylhalogeniden zu 3-Aryl-5-methyl-l,2,4-oxadiazol-4-oxiden um56 ... 

In Essigsaureanhydrid werden 4-Amino-ptcridin-3-oxide aufgespallen, wobei unter dem Einbau eines Ace-tyl-Rcstcs 3-(3-Formylamino-2-pyrazyl)-1,2,4-oxadiazole entstehcn290 z.B. ... 

Bis(perfluoroalkyl)-l,3,4-oxadiazoles (285) are attacked readily by hydrazine with ring opening and formation of the perfluoroacylated hydrazidines (286). Concurrent dehydration and oxidation of these intermediates with iron(III) chloride produces the corresponding 3,6-bis(perfluoroalkyl)-l,2,4,5-tetrazines (287). Ring closure of (286) without oxidation produces the corresponding 3,5-bis(perfluoroalkyl)-4-amino-l,2,4-triazoles (66JOC781). 

Oxidation of oxalic acid with dimethyl-V,V-dichlorohydantoin and dichloroisocya-nuric acid is of first order with respect to the oxidant. The order with respect to the reductant is fractional. The reactions are catalysed by Mn(II). Suitable mechanisms are proposed.129 A mechanism involving synchronous oxidative decarboxylation has been suggested for the oxidation of a-amino acids with l,3-dichloro-5,5-dimethylhydantoin.130 Kinetic parameters have been determined and a mechanism has been proposed for the oxidation of thiadiazole and oxadiazole with trichloroiso-cyanuric acid.131 Oxidation of two phenoxazine dyes, Nile Blue and Meldola Blue, with acidic chlorite and hypochlorous acid is of first order with respect to each of the reductant and chlorite anion. The rate constants and activation parameters for the oxidation have been determined.132... 

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