Acetic Acid → Oxazole

Participants

Reaction Steps

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).

Provenance & Evidence