Oxazole

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Oxazoles
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Oxazole
Full structural formula
Skeletal formula with numbers
Ball-and-stick model
Space-filling model
Names
Preferred IUPAC name
1,3-Oxazole[1]
Identifiers
3D model (
JSmol
)
103851
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.005.474 Edit this at Wikidata
EC Number
  • 206-020-8
485850
MeSH D010080
UNII
  • InChI=1S/C3H3NO/c1-2-5-3-4-1/h1-3H ☒N
    Key: ZCQWOFVYLHDMMC-UHFFFAOYSA-N ☒N
  • InChI=1/C3H3NO/c1-2-5-3-4-1/h1-3H
    Key: ZCQWOFVYLHDMMC-UHFFFAOYAD
  • C1=COC=N1
Properties
C3H3NO
Molar mass 69.06 g/mol
Density 1.050 g/cm3
Boiling point 69.5 °C (157.1 °F; 342.6 K)
Acidity (pKa) 0.8 (of conjugate acid)[2]
Hazards
GHS labelling:[3]
GHS02: FlammableGHS05: Corrosive
Danger
H225, H318
P210, P233, P240, P241, P242, P243, P264+P265, P280, P303+P361+P353, P305+P354+P338, P317, P370+P378, P403+P235, P501
Supplementary data page
Oxazole (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Oxazole is the parent compound for a vast class of

pKa of 0.8, compared to 7 for imidazole
.

Preparation

The classic synthetic route the Robinson–Gabriel synthesis by dehydration of 2-acylaminoketones:

The Robinson–Gabriel synthesis
The Robinson–Gabriel synthesis

The Fischer oxazole synthesis from cyanohydrins and aldehydes is also widely used:

Fischer Oxazole Synthesis
Fischer Oxazole Synthesis

Other methods are known including the reaction of α-

haloketones and formamide and the Van Leusen reaction with aldehydes and TosMIC
.

Biosynthesis

In

peptides:[5]

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.

Reactions

With a pKa of 0.8 for the conjugate acid (oxazolium salts), oxazoles are far less basic than imidazoles (pKa = 7).

isonitrile, which can be trapped by silylation.[4]

electron donating groups
.

Nucleophilic aromatic substitution takes place with leaving groups at C2.

Diels–Alder reactions involving oxazole (as dienes) and electrophilic alkenes has been well developed as a route to pyridines. In this way, alkoxy-substituted oxazoles serve a precursors to the pyridoxyl system, as found in vitamin B6. The initial cycloaddition affords a bicyclic intermediate, with an acid-sensitive oxo bridgehead.

Use of an oxazole in the synthesis of a precursor to pyridoxine, which is converted to vitamin B6.[6]


In the Cornforth rearrangement of 4-acyloxazoles is a thermal rearrangement reaction with the organic acyl residue and the C5 substituent changing positions.

  • Various
    oxidation reactions. One study[7] reports on the oxidation of 4,5-diphenyloxazole with 3 equivalents of CAN to the corresponding imide and benzoic acid
    :
Oxazoline CAN oxidation
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).


See also

Additional reading

  • Fully Automated Continuous Flow Synthesis of 4,5-Disubstituted Oxazoles Marcus Baumann, Ian R. Baxendale,
    doi:10.1021/ol061975c

References

  1. ISBN 978-0-85404-182-4
    .
  2. ^ Zoltewicz, J. A. & Deady, L. W. Quaternization of heteroaromatic compounds. Quantitative aspects. Adv. Heterocycl. Chem. 22, 71-121 (1978).
  3. ^ "Oxazole". pubchem.ncbi.nlm.nih.gov.
  4. ^
    ISBN 0-582-01421-2
    .
  5. PMID 10331285
    .
  6. ISBN 978-3-527-30673-2
    .
  7. doi:10.1021/ol0624530
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