Davidson oxazole cyclization

What is Davidson oxazole cyclization?

While Japp initially investigated this reaction, it was Davidson et. al. who studied the mechanism and developed a general procedure for preparing substituted oxazoles, giving rise to the name Davidson oxazole cyclization or Davidson cyclization. This reaction involves condensing O-acylacylions with ammonia NH3 or ammonium acetate NH4OAc to form substituted oxazoles. O-acylacyloins or O-acyl benzoin can be prepared by reacting acyloin or benzoin with carboxylic acid using N,N’-dicyclohexylcarbodiimide DCC, or by reacting α-haloketones with carboxylic acid under basic conditions.

Davidson oxazole cyclization - Davidson cyclization - general reaction scheme
Davidson oxazole cyclization

It has been observed that organic amines cannot replace ammonia or ammonium acetate in this reaction. This method is most effective for 2,4,5-trisubstituted oxazoles or those with an aromatic substituent at C-5, but is less successful for preparing 2,4-disubstituted or monosubstituted oxazoles.