EZ-isomerization of alpha,beta-unsaturated acid derivatives in the solid state

The solid-state EZ-isomerizability of alpha,beta-unsaturated amide was greatly improved by modifying their structure, which had low isomerizability in the solid state; EZ-isomerizability was attained by replacing the carbonyl group of the amides by a thiocarbonyl group as well as replacing the heterochiral N-substituent of the amides by a homochiral one. Furthermore, EZ-photoisomerization was also attained for several kinds of salts of alpha,beta-unsaturated carboxylic acids with amines. This photoreaction was proven to be an effective method for preparing (Z)-isomers from ammonium (E)-alpha,beta-unsaturated carboxylates. The isomerizability was strikingly altered upon changing the ammonium part, which implied that the crystal structure affected the reactivity to a considerable extent. A further detailed study concerning the crystal structures suggested that the characteristic of the hydrogen-bond network had a close correlation with the isomerizability. Moreover, both the bulkiness of the carboxylate and ammonium parts as well as their difference in length were considered to be the most important factors influencing the isomerizability.