Recyclization of 2-aryl-4-cyano-5-hydrazinooxazoles

The available 2-benzoylamino-3,3-dichloroacrylonitrile and its analogs when treated with excess hydrazine hydrate convert to 2-aryl-4-cyano-5-hydrazin ooxazoles. The products are fairly stable in usual conditions but undergo r ecyclization on heating in acetic acid to give previously unknown derivativ es of 2-methyl-1,3,4-oxadiazole with a 5-acylamino(carbamoyl)methyl substit uent, whose structure was established by spectroscopy and X-ray diffraction . An important role in this complex transformation is probably played by pr ototropic forms of 4-cyano-5-hydrazinooxazoles, viz. hydrazones of substitu ted 2-oxazolin-5-ones which are not aromatic and thus can be cleaved with a cetic acid and then recyclize.