Acetic Acid → Oxazole

HRID 1181014Notes

Reaction equation

[C:1]([O-:4])(=[O:3])[CH3:2].[NH4+:5].[C:6]([OH:9])(=O)[CH3:7]>>[C:1]([O-:4])(=[O:3])[CH3:2].[NH4+:5].[O:9]1[CH:6]=[CH:7][N:5]=[CH:1]1

Participants

Reactant 2

HCID 176Acetic Acid

HCID 517165Ammonium Acetate

Product 2

HCID 9255Oxazole

HCID 517165Ammonium Acetate

Procedure

An alternative synthetic route to oxazole tailpiece is shown in Reaction Scheme 24. Carboxylic acid (106) is condensed with 2-bromo-3-oxopentanoate (preferably methyl ester) (107) to give ketoester (108). The latter is converted to an intermediate enamine (109) by treatment with anhydrous ammonium acetate. Subsequent cyclization of compound (109) in acetic acid in the presence of anhydrous ammonium acetate gives compound (110). The use of anhydrous ammonium acetate obtained by azeotropic evaporation with ethanol eliminates water in the reaction, which causes decarboxylation of compound (110). Additionally, some of the water liberated in the reaction is removed at the enamine stage. These modifications along with a simplified isolation procedure lead to higher yields of oxazole (110).

Sources & evidence

ORD record: ord-a89dd88a01b747d2ba14ca36585451cb
Source dataset: uspto-grants-2007_10
DOI: 10.6084/m9.figshare.5104873.v1
Patent number: US07282501B2

Reaction notes

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