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

Abstract

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