Synthesis and Reaction of 5-Substituted 2-Alkoxy-1, 3, 4-oxadiazoles

Abstract

Treatment of aromatic aldehyde or crotonaldehyde N-alkoxycarbonylhydrazones [1 a-e] with lead tetraacetate afforded 5-substituted 2-alkoxy-1, 3, 4-oxadiazoles [2 a-e]. However, similar treatment of butylaldehyde N-ethoxycarbonylhydrazone [1 f] with lead tetraacetate gave 5-propy1-2-ethoxy-1, 3, 4-oxadiazole [2 f] along with ethyl 1-acetoxybutylazoformate[3 f].
Upon treatment of [2a- c, 2e, 2f] with tertiary amines, the alkyl moiety of alkoxyl grou ps at the 2-position migrated to the nitrogen at the 3-position to give 5-substituted 3-alkyl-2, 3dihydro-1, 3, 4-oxadiazol-2-ones [4 a-c, 4 e, 4 f]. The rate of this migration depended on the amines employed, decreasing in the order: 1, 5-diazabicyclo[5.4.0]undec-5-ene (DBU) >triethylamine> pyridine. The ease of migration of the alkyl group decreased in the order: methyl>ethyl> isopropyl.