STRUCTURAL EFFECTS ON THE ISOINDOLE-ISOINDOLENINE EQUILIBRIUM - SUBSTITUTION IN THE PYRRYL RING

The influence of substitution in the pyrryl ring on the isoindole-isoindolenine equilibrium has been studied by NMR spectroscopy. Electron-releasing groups selectively stabilize the isoindolenine tautomer in which the substituent is conjugated with the π-system, while electron-withdrawing groups have the opposite effect. However, sequential introduction of identical groups into the 1- and 3-positions leads, first to a shift of the equilibrium in one direction, then to a shift in opposite direction. Reasons for this behavior are discussed. © 1979.