Rearrangements Involving a Side-Chain CNN

During the last few years, the reactivity of the widely studied (81AHC141) sequence XYZ = CNN has been considered for some special aspects. Arylhydrazones of 3-benzoyl-1,2,4-oxadiazoles and 3-benzoyli- 

From the 3-acetyloxadiazole 54 (R = Me), both E and Z phenylhydra-zones55(R = Me R = H) are obtained, the isomer being the predominant component. As expected, both isomers rearrange on melting into the triazole 57 (R = Me), whereas the base-induced rearrangement takes place preferably from the Z isomer only (90UP1). 

On reacting with aqueous bases or acids, isoxazolin-5-one phenylhydra- 

These results show the greater stability of a 1,2,3-triazole compared with a 1,2,5-oxadiazole. As confirmation, CNDO/2 calculations on model compounds 76 and 77 are also reported. This approach shows that (a) the triazole 77 is about 20 kcal mol more stable than the oxadiazole 76 and (b) the 7T bond order of the O—N bond is lower than that of N—N (85HCA1748). The occurrence of a rearrangement by electronic impact is also shown in the mass spectra of 74Z the fragment at m/z (M-17) is ascribed to the formation of the rearranged product (85HCA1748). 

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