5-(4H)-oxazolona - 5-(4H)-oxazolona

IUPAC name
Other names 1,3-Oxazol-5(4H)-ona
Molecular formula C 3 H 3 NO 2
CAS number 497-24-5[1]
PubChem 12313817
Physical properties
Density 1414 kg/; 1414 g/cm³
Molar mass 85.06 g / mol
Boiling point 105,542 °C (379 K)
Refractive index (n D ) 1,548
Chemical properties
Acidity 9,0 pKa
Values ​​in the SI and under standard conditions
(25 and 1 atm ), unless otherwise indicated.

The 5- (4H) -oxazolone is a chemical compound of the family of the oxazole . This chemical compound with the molecular formula C 3 H 3 NO 2 , has several reactive sites that allow its functionalization in various ways, although most reactions involve the reaction with the C-4 proton (starting it with a base or producing an aromatic nucleophilic substitution reaction ), or the reaction and subsequent ring opening.

Synthesis and general reactivity

Since Erlenmeyer's discovery of the synthesis of azlactones (by means of the Erlenmeyer-Plöchl synthesis of amino acids ), other new syntheses of 5- (4H) -oxazolones have been discovered (hereinafter neither the position of the double bond will be specified nor the ketone, in such a way that we will name this chemical compound as oxazolone, although we refer only to this isomer).

The acidic nature of the proton at position 4 of the oxazolone ring (the C-4), which has a pK at ~ 9, makes the formation of oxazole enolate easy to form ( compound [B] of figure 1) , being able to react with bases to give these enolates. Furthermore, it also reacts with nucleophiles and electrophiles , depending on whether the reagent is of one type or another. [ 2 ]

  • If it reacts with a base, due to chemical equilibrium ( keto-enol tautomerism ), the enolate ( compound [B] ) and the ketonic form ( compound [A] ) are formed, being able to react with a wide range of electrophiles.
  • If it reacts with a nucleophile, it attacks the carbonyl carbon 5 (C-5) atom, opening the oxazolone ring, producing compound [C] in the figure.
  • If it reacts with a Lewis acid (AL), 2 compounds of different reactivity can be formed: a 1,3- dipolarophile ( compound [D] ), which can react in a 1,3-dipolar cycloaddition ; or a ketene ( compound [E] ), which may give a cycloaddition [2 + 2].

Figure 1: general reactivity of 5- (4H) -oxazolones


  1. CAS number
  2. Jason S. Fisk, Robert A. Mosey y Jetze J. Terpe (2007). «The diverse chemistry of oxazol-5-(4H)-ones». Chem. Soc. Rev. 36: 1432-1440. doi:10.1039/b511113g.