EN
2-Phenyl-4-alkyl-4-hydroxymethyl-1,3-oxazolones (2a-d) have been identified as side products accompanying activation of N-benzoyl-2-alkylserines (1a-d). Oxazolones 2a-d in the presence of amine rearrange subsequently to corresponding 4-alkyl-2- phenyl-4,5-dihydro-1,3-oxazole-5 carboxylic acids (4a-d) at a 20-68% yield.