3-Acetylamino-5-phenyl-l,2.4-oxadiazole

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. 

One of the earlier examples of a degenerate ring transformation involving the participation of a three-atom side chain is the interconversion of the isomers 3-benzoylamino-5-methyl-l,2,4-oxadiazole (133, X = H) and 3-acetylamino-5-phenyl-l,2,4-oxadiazole (134, X = H) (Scheme IV.51) (75JHC985 89H(29)737). Heating each of these compounds at 181°C furnished an identical equilibrium mixture of isomers, in which mixture isomer 134 (X = H) is predominant (X134/133 at 181°C is about 6.4). These data indicate that the conversion of isomer 133 (X = H) into 134 (X = H) is dri-... 

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