Unusual Formation of Oxazoles by Base- or Acid-catalyzed Ring Opening of 2-Acyl-2H-azirines

Abstract

Formation of 2-acyl-2H-azirines was confirmed in thermolyses of 8-acylvinyl azides to establish the generality of azirine formation from vinyl azides.Unusual C-C bond fission of 3-unsubstituted 2acyl-2H-azirine to give oxazole was found to be a base catalyzed reaction.On the other hand, 3-substituted analogues were found to undergo acid-catalyzed reaction to give oxazoles.Maiorana reported that thermolysis of 6-azid~methacr~lophenone 2 gave 4-methyl-5-phenylisoxazole 5 besides 2-benzoylpropionitrile 3a,l whereas