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Oxazole is the parent compound for a vast class of heterocyclic aromatic organic compounds. These are azoles with an oxygen and a nitrogen separated by one carbon.[2] Oxazoles are aromatic compounds but less so than the thiazoles. Oxazole is a weak base; its conjugate acid has a pKa of 0.8, compared to 7 for imidazole.

Oxazole
Full structural formula
Skeletal formula with numbers
Ball-and-stick model
Space-filling model
Names
IUPAC name
1,3-oxazole
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.005.474
EC Number
  • 206-020-8
MeSH D010080
Properties
C3H3NO
Molar mass 69.06 g/mol
Density 1.050 g/cm3
Boiling point 69 to 70 °C (156 to 158 °F; 342 to 343 K)
Acidity (pKa) 0.8 (of conjugate acid) [1]
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Thermodynamic
data
Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

PreparationEdit

Classical oxazole synthetic methods in organic chemistry are

Other methods:

 
 

BiosynthesisEdit

In biomolecules, oxazoles result from the cyclization and oxidation of serine or threonine nonribosomal peptides:

 
Where X = H, CH
3
for serine and threonine respectively, B = base.
(1) Enzymatic cyclization. (2) Elimination. (3) [O] = enzymatic oxidation.

Oxazoles are not as abundant in biomolecules as the related thiazoles with oxygen replaced by a sulfur atom.

ReactionsEdit

 
In the balanced half-reaction three equivalents of water are consumed for each equivalent of oxazoline, generating 4 protons and 4 electrons (the latter derived from CeIV).
 
Use of an oxazole in the synthesis of a precursor to pyridoxine, which is converted to vitamin B6.[7]

See alsoEdit

ReferencesEdit

  1. ^ Zoltewicz, J. A. & Deady, L. W. Quaternization of heteroaromatic compounds. Quantitative aspects. Adv. Heterocycl. Chem. 22, 71-121 (1978).
  2. ^ Heterocyclic Chemistry TL Gilchrist, The Bath press 1985 ISBN 0-582-01421-2
  3. ^ A new consecutive three-component oxazole synthesis by an amidation–coupling–cycloisomerization (ACCI) sequence Eugen Merkul and Thomas J. J. Müller Chem. Commun., 2006, 4817 - 4819, doi:10.1039/b610839c
  4. ^ Fully Automated Continuous Flow Synthesis of 4,5-Disubstituted Oxazoles Marcus Baumann, Ian R. Baxendale, Steven V. Ley, Christoper D. Smith, and Geoffrey K. Tranmer Org. Lett.; 2006; 8(23) pp 5231 - 5234; (Letter) doi:10.1021/ol061975c
  5. ^ They react together in the first phase in a continuous flow reactor to the intermediate enol and then in the second phase in a phosphazene base (PS-BEMP) induced cyclization by solid-phase synthesis.
  6. ^ "Ceric Ammonium Nitrate Promoted Oxidation of Oxazoles", David A. Evans, Pavel Nagorny, and Risheng Xu. Org. Lett.; 2006; 8(24) pp 5669 - 5671; (Letter) doi:10.1021/ol0624530
  7. ^ Gérard Moine, Hans-Peter Hohmann, Roland Kurth, Joachim Paust, Wolfgang Hähnlein, Horst Pauling, Bernd–Jürgen Weimann, Bruno Kaesler (2011). "Vitamins, 6. B Vitamins". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.o27_o09.CS1 maint: uses authors parameter (link)