1.2.4- Oxadiazole, 5- -3-phenyl rearrangement

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 role of substituents X on the mononuclear heterocyclic rearrangement (MHR) of 20 phenylhydrazones 54 of 3-benzoyl-5-phenyl-l,2,4-oxadiazole into the triazoles 55 (Equation 2) has been investigated, allowing the influence of X on the product distribution to be evaluated and first-order rate constants and Hammett correlations to be determined <1999T12885>. 

Amino derivatives of 1,2,4-oxadiazoles, isoxazoles, and 1,2,5-oxadiazoles interact with phenyl isocyanate to produce various 3-substituted 5-amino-l,2,4-thiadiazoles, via intermediate thioureides which can be isolated. The tendency to rearrange follows the order 1,2,4-oxadiazoles, isoxazoles, and 1,2,5-oxadiazoles <1996CHEC-II(4)307>. 

A few examples, illustrating the principle of this type of degenerate rearrangement, are the thermo-induced equilibrium shift of 3-benzoylamino-5-methyl-l,2,4-oxadiazole into 3-acetylamino-5-phenyl-l,2,4-oxadiazole and the isomerization of 5-benzoyl-methylfuroxan oxime into 4-[a-nitroethyl]-3-phenylfurazan (82G181) (Scheme 1.8). They are extensively discussed in Chapter IV. 

Isomerization and Rearrangement of E Arylhydrazones of 3-Benzoyl-5-phenyl-1,2,4-oxadiazoles... 

Alkyl-3-aminoisoxazoles, 5-alkyl-3-amino-l,2,4-oxadiazoles, and 5-alky 1-3-amino-1,2,5-oxa-diazoles, when heated with phenyl isothiocyanate produce the corresponding thioureas (308) (Equation (46)), (310) (Equation (47)) and (312) (Equation (48)) which subsequently rearrange by a common mechanism to yield 1,2,4-thiadiazoles (309), (311), and (313), respectively <84CHEC-I(6)463>. 

Examples of the rearrangement of 1,2,4-oxadiazoles into 1,2,3-triazoles were discovered by Ruccia and co-workers178, 179 and earlier by Gramantieri180 as shown in Eq. (68).179 In the example selected, the product 93 was obtained directly from the reaction with phenyl-... 

The kinetics for rearrangement of di-, tri-, tetra-, and penta-substituted (Z)-arylhy-drazones of 3-benzoyl-5-phenyl-l,2,4-oxadiazole to 2-aryl-4-benzoylamino-5-phenyl-... 

Heating 5-alkyi-3-amino-l,2,4-oxadiazoIes, 5-alkyl-3-aminoisoxazoIes and 4-alkyl-3-amino-l,2,5-oxadiazoles with phenyl isothiocyanate produces the corresponding thioureas (344), (343) and (345) which rearrange by a common mechanism to the 1,2,4-thiadiazoles (372), (373) and (374), respectively (Schemes 134, 135, 136) (74CC358, 77JCS(P1)1616). 

The thermolysis of 2-methyl-5-phenyl-l,3,4-oxadiazol-2-(3H)-one 106 produces a nitrile imine intermediate 105 which rearranges to the carbodiimide 107. The same carbodi-imide is obtained in the thermolysis of 2-methyl-5-phenyltetrazole 104. 

Rearrangement of furazan derivatives were studied by Boschi and coauthors [67]. 4-Phenyl-1,2,5-oxadiazole sulfone 130 (Scheme 45) heated in acetone containing sodium hydroxide rearranged to sulfinic acid derivative 132. After expulsion of SO2,3-acetamido-4-phenylfurazan 133 was formed in 86% yield. Amido-sulfide 131 under similar conditions underwent hydrolysis only to afford the respective acid. 

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