Mononuclear heterocyclic rearrangements—vi : Conversion of 1,2,4-oxadiazoles into imidazoles

Abstract

The rearrangement of N - (1,2,4 - oxadiazol - 3 - yl)β - enamino ketones 3 a–d and N-(1,2,4 - oxadiazol - 3 - yl)β - enaminoesters 3 e–h into 2 - acylamino - imidazolyl derivatives 9 a–h by the action of sodium ethoxide in N,N-dimethylformamide is the first example of a mononuclear heterocyclic rearrangement involving a nucleophilic carbon. Compounds prepared by condensation of 3 - amino - 1,2,4 - oxadiazoles 1 a–b with β - dicarbonyl compounds 2 a–d, show spectroscopic properties in agreement with cis-chelated structures 4. By condensation between 1 a–b and benzoylacetic ester 2 d, N - (1,2,4 - oxadiazol - 3 - yl)β - ketoamides 6 a–b have been obtained as secondary products. In solution, these compounds are in equilibrium with the corresponding tautomers 7 a–b.