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Chemical structure of the 5-(4H)-oxazolone isomer

Oxazolone is a chemical compound and functional group, with the molecular formula C3H3NO2. It was named in-line with the Hantzsch–Widman nomenclature and is part of a large family of oxazole based compounds. There are a total of 5 structural isomers of oxazolone; 3 according to the location of the carbonyl group and 2 more according to the location of the double bound C=X (with X= N or C):

  • 2-(3H)oxazolone.
  • 2-(5H)oxazolone.
  • 4-(5H)-oxazolone.
  • 5-(2H)-oxazolone.
  • 5-(4H)-oxazolone.

The 4-oxazolone motif, which is also formally a lactam, is present in a number of drugs (fenozolone, thozalinone, cyclazodone, reclazepam etc.).

Substituted 5-oxazolones may also be regarded as the cyclization products of N-acyl α-amino acids, making them lactones, and are sometimes referred to as azlactones.[1][2]

See also[edit]


  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "azlactones".
  2. ^ K. Mukerjee, Arya (1987). "Azlactones: Retrospect and Prospect". HETEROCYCLES. 26 (4): 1077. doi:10.3987/R-1987-04-1077.