E,Z-ISOMERIZATION STUDIES OF ETHYL 2-OXO-3-INDOLINYLIDENECYANOACETATES BY H-1-NMR SPECTROSCOPY

The kinetics of base-catalysed E/Z isomerization for a series of ethyl 2-oxo-3-indolinylidenecyanoacetates in CDCl3. solutions were studied by H-1 NMR spectroscopy. Both polarizable double bond considerations and steric requirements of the base must be considered in explaining the results. The E/Z equilibrium of ethyl 1-carbethoxy-2-oxo-3-indolinylidenecyanoacetate was reached faster than those of ethyl 2-oxo-3-indolinylidenecyanoacetate and the 1-methyl derivative by a factor of ca. 10 in the presence of triethylamine, and the isomerizations were faster when quinuclidine was used. In pure DMSO-d6 solutions, the equilibria were established upon dissolution, but addition of small amounts of acid slowed the isomerization process in these systems.