Evidence of the structure of 4-(4′-acetoxybenzylidene)-2-methyl-5-oxazolone and its phenylpropenoic acid derivatives

4-(4′-Acetoxybenzylidine)-2-methyl-5-oxazolone (Z-isomer) was synthesized, which upon basic hydrolysis yielded the unexpected 2-acetoxy-3-(p-hydroxyphenyl)-propenoic acid and treatment with acetic acid formed 2-acetoxy-3-(p-acetoxyphenyl)-propenoic acid. The structures of the three compounds were assigned by NMR spectroscopy. An X-ray crystallographic study of the starting azlactone confirmed its structure and supported the fact that the Z-configuration was retained during the synthesis of the phenylpropenoic acid derivatives.