Abstract Several Z-2-methyl (or phenyl)-4-[α-arylethylidene]-5 (4H)-oxazolones 3Z, 4Z were prepared. The results obtained were compared by diazomethane insertion and condensation procedure. In order to synthesize E-2-phenyl-4-[α-arylethylidene]-5 (4H)- oxazolones 4E hydrogen bromide isomerization in dry benzene was used.