Ring transformations of heterocycles. Part1. Transformation of 4-amino-Δ2-1,2,4-oxadiazolines into 1,3,4-oxadiazoles

3-Aryl-4-amino-δ2-1,2,4-oxadiazolines 3 and their N-chloroacetyl derivatives 4, upon treatment with chloroacetic anhydride in refluxing toluene, afford 2-chloromethyl-5-aryl-1,3,4-oxadiazoles 5, suggesting the conversion sequence 3 → 4 → 5. The generality of the new ring transformation 4 → 5 is supported similar conversion of other 4-(acylamino)-1,2,4-oxadiazolines 8 to 1,3,4-oxadiazoles 9.