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Names | |||
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Preferred IUPAC name 1,3-Oxazole | |||
Identifiers | |||
CAS Number |
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3D model (JSmol) | |||
Beilstein Reference | 103851 | ||
ChEBI | |||
ChEMBL | |||
ChemSpider |
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ECHA InfoCard | 100.005.474 | ||
EC Number |
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Gmelin Reference | 485850 | ||
MeSH | D010080 | ||
PubChem CID | |||
UNII | |||
CompTox Dashboard (EPA) | |||
InChI
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SMILES
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Properties | |||
Chemical formula | 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) | ||
Hazards | |||
GHS labelling: | |||
Pictograms | |||
Signal word | Danger | ||
Hazard statements | H225, H318 | ||
Precautionary statements | 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 , 100 kPa). N verify (what is YN ?) Infobox references |
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. 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.
The classic synthetic route the Robinson–Gabriel synthesis by dehydration of 2-acylaminoketones:
The Robinson–Gabriel synthesisThe Fischer oxazole synthesis from cyanohydrins and aldehydes is also widely used:
Fischer Oxazole SynthesisOther methods are known including the reaction of α-haloketones and formamide and the Van Leusen reaction with aldehydes and TosMIC.
In biomolecules, oxazoles result from the cyclization and oxidation of serine or threonine nonribosomal peptides:
Where X = H, CHOxazoles are not as abundant in biomolecules as the related thiazoles with oxygen replaced by a sulfur atom.
With a pKa of 0.8 for the conjugate acid (oxazolium salts), oxazoles are far less basic than imidazoles (pKa = 7). Deprotonation of oxazoles occurs at C2. Formylation with dimethylformamide gives 2-formyloxazole. The lithio compound exists in equilibrium with the ring-opened enolate-isonitrile, which can be trapped by silylation.
Electrophilic aromatic substitution takes place at C5, but requiring 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.
In the Cornforth rearrangement of 4-acyloxazoles is a thermal rearrangement reaction with the organic acyl residue and the C5 substituent changing positions.