Vinylacidic Acid in the Reaction of Aza-Michael with1-Ethylpyrazole

Commercial vinylacetic acid is a mixture of isomers of but-3-enoic and but-2-enoic acids. It was shown that but-3-enoic acid undergoes isomerization in the presence of a catalytic amount of 1-ethylpyrazole. The resulting Z- and E-isomers of but-2-enoic acid enter the aza-Michael reaction with pyrazole. The1H NMR analysis showed that by the end of the experiment the ratio of unreacted Z- andE-isomers of but-2-enoic acid in the reaction mixture decreased by half (to 3 : 1), which pointed to a higher reactivity of the Z-isomer.