Benzonitrile A-oxides

Reaction of benzonitrile A-oxide with alkynic phosphinate (343) gave exclusively 5-phosphinylisoxazole (344), whereas reaction with enamine phosphinate (345) gave the otherwise inaccessible 5-unsubstituted 4-phosphinylisoxazole (346) (80JOC529). 

Reaction of benzonitrile A-oxide with benzoylacetylene gave a mixture of 4-benzoyl-isoxazole (347) and 5-benzoylisoxazole (348), whereas that with )3-enaminone (349) gave exclusively 4-benzoylisoxazole (347) (71S433) and that with chloroenone (350) gave exclusively 5-benzoylisoxazole (348) (70S344). 

The reaction of benzonitrile A-oxide with a- and )3-azidostyrenes (351) and (352) gave 3,5- and 3,4-diphenylisoxazoles (353) and (354), respectively, in good yields (74JOC1221). Clearly, the X function has a pronounced directional effect on this type of 1,3-cycloaddition... 

The ynaminoketone vinylogs react with 1,3-dipoles (C,N-disubstituted nitii-limines, benzonitrile A-oxide) in a regio- and stereospecific fashion at the triple... 

In particular, the reactions of electrophilically activated benzonitrile A-oxides with 3-methylenephthalimidines with formation of 2-isoxazolines and oximes and the cycloaddition between alkynyl metal(O) Fischer carbenes and nitrones leading to 4-isoxazolines have been investigated by density functional theory methods <06JOC9319 06JOC6178>. 

The addition of the anion of a-bromo-a-nitrotoluene (564) to cyclohexene gave the hexahydro derivative (565) of 3-phenyl-l,2-benzisoxazole (75TL2131). An unusual hexahydro derivative (566) was produced by the bis addition of benzonitrile A-oxide to benzoquinone (67AHC(8)277). 

Alkyl but-3-en-1-yn-l-yl tellurium compounds add benzonitrile A-oxide, N-phenylbenzylidenimine A-oxide and benzonitrile phenylimine across the carbon-carbon double bond forming heterocyclic compounds. The carbon-carbon triple bond remains unaffected. 

Diphenylisoxazole has been synthesized by the reaction of benzonitrile A-oxide with / -azidostyrene (352) (74JOC1221). 

Isoxazole-3-carbaIdehyde has been obtained as a minor product from the reaction of acetylene with a mixture of nitric oxide and nitrogen dioxide (61JOC2976). Although 3-aryl-4-formylisoxazoles have been synthesized in good yields from the reaction of benzonitrile A-oxides with 3-(dimethylamino)-2-propen-l-one (71S433), the parent member of the series, isoxazole-4-carbaldehyde, has never been reported. It may possibly be obtained by the addition of fulminic acid to 3-(dimethylamino)-2-propen-l-one. 

Chloro- and 5-bromo-isoxazoles have been prepared by reaction of 5-isoxazolones with the appropriate phosphoryl halide (77JMC934). 3-Phenyl-5-trifluoromethylisoxazole has been synthesized by reaction of benzonitrile A/-oxide with 3,3,3-trifluoropropyne (77JMC934). 

The 2-methyl-4,5-dihydrooxazoles (358 Z = O) or 2-methyl-4,5-dihydrothiazole (358 Z = S) undergo 1,3-dipolar cycloaddition reactions with benzonitrile A -oxide to give the corresponding 7a-methyl-3-phenyl-5,6-dihydro-7a//-oxazolo[3,2- ][l,2,4]oxadiazoles (16) or -thiazolo[3,2-c ]-[l,2,4]oxadiazoles (17) (Equation (121)) <92T7703>. 

The cyclization of the ketone 375 with benzonitrile A/-oxide (40°C, Et20,24 h) occurs in a similar manner to produce 4-(3-oxobut-1 -en-1 -yl)-3-phenyl-5-diethyl-aminoisoxazole (383) in 27% yield (94ZOR46). 

The reaetion of 4-dialkylamino(alkoxy)but-3-en-2-one with benzonitrile N-oxide (35°C, EtaO, 8 h) follows a seheme of 1,3-dipolar eyeloaddition with elimination of ammonia, the eorresponding amine, or aleohol to form 3-phenyl-4-aeetylisoxazole 324 in 60-67% yield (83ZOR2281). 

The relatively high aromaticity of the parent 1,2,5-thiadiazole renders it good thermal stability (stable up to 220 °C) despite this, 3,4-diphenyl-l,2,5-thiadiazole 8 suffers slow photochemical degradation to give benzonitrile and sulfur. The low basicity of 1,2,5-thiadiazole indicates a relatively high electron density in the Jt-orbital and corresponding low electron density of the nitrogen lone pairs. Addition reactions such as Walkylation do not occur readily. A-Oxidation is... 

Chemical/Physical. Diuron decomposes at 180 to 190 °C releasing dimethylamine and 3,4-dichlorophenyl isocyanate. Dimethylamine and 3,4-dichloroaniline are produced when hydrolyzed or when acids or bases are added at elevated temperatures (Sittig, 1985). The hydrolysis half-life of diuron in a 0.5 N NaOH solution at 20 °C is 150 d (El-Dib and Aly, 1976). When diuron was pyrolyzed in a helium atmosphere between 400 and 1,000 °C, the following products were identified dimethylamine, chlorobenzene, 1,2-dichlorobenzene, benzonitrile, a trichlorobenzene, aniline, 4-chloroaniline, 3,4-dichlorophenyl isocyanate, bis(l,3-(3,4-dichlorophenyl)urea), 3,4-dichloroaniline, and monuron [3-(4-chlorophenyl)-l,l-dimethylurea] (Gomez et al., 1982). Products reported from the combustion of diuron at 900 °C include carbon monoxide, carbon dioxide, chlorine, nitrogen oxides, and HCl (Kennedy et al., 1972a). 

Further comparisons of experimental versus estimated values are discussed, for example, for hydroxyureas [57]. Based on new experimental K0w for substituted a,N-diphenylnitrones and benzonitrile iV-oxides, Kirchner et al. [58] evaluated contributions for several iV-oxide groups for which contribution values were so far missing in the scheme of Hansch and Leo. Similarly, Finizio et al. [35] derived new contributions for three s-triazine groups. The groups and their contributions are shown in Figures 1.7.6 and 1.7.7. 

Kirchner, J. J., et al., Octanol-Water Partition Coefficients of Substituted. a,V-Diphe-nylnitrones and Benzonitrile V-Oxides. J. Pharm. Sci., 1985 74, 1129-1130. 

Cations of the type 265, possessing both a thiopyrylium and a dithiole ring, when treated with triethylamine lead to unstable neutral compounds. However, if the reaction is followed by the addition of benzohydroxymoyl chloride [PhC(=NOH)CI], which in situ generates benzonitrile N-oxide, compounds of the type 266 are obtained. A mechanism has been suggested for such transformation [80BSF(2)577]. 

Phenyl-[l, 2,4]triazolo[ 1,5-a Jpyrazines have been prepared by the oxidative ring closure of fV(2)-pyrazinylbenzamidines (344) as shown in Scheme 60. The benzamidines were synthesized from 2-aminopyrazines and benzonitrile, a reaction that failed with aliphatic nitriles (64JOC2542). 

Using diazoalkanes results in the formation of isomeric mixtures of cycloadducts.Unlike some reactants (phenyl azide, tosyl azide and diphenylnitrilimine), benzonitrile oxide, diazomethane, and A-phenylbenzylideneamine A-oxide underwent [3 4- 2] cycloaddition on mixing with lumisantonin using A -phenylbenzylideneamine A-oxide, however, gave the product cycloadduct in 8% yield.Dihydropyrazoles were obtained in some cases.Furthermore, pyrrole derivatives were obtained in low yield by intramolecular addition of an azomethine ylide to an a- and / -monocyclopropyl acrylate moiety. 

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