| Abstract
| - The reactions of 5-substituted indolylmalonates (2a−e), carrying an electron-withdrawing groupat the N(1) position, with bromine in CCl4 or AcOH are reported. These substrates undergo oxidationin competition with the well-known aromatic bromination. Under the two sets of conditions, withparent indolylmalonate (2a), chemospecific oxidation is observed, whereas with 5-hydroxyindolylmalonate (2c), bromination at the 4- and 6-position is the dominating reaction. Investigation ofthe products composition of several 5-substituted indolylmalonates revealed the following trend: with a 5-substituted electron-withdrawing group like fluorine, the indolylmalonate undergoesoxidation rather than bromination. In contrast, with a 5-substituted electron-donating group, likea hydroxyl group, the ring bromination occurs preferentially over the oxidation. When the5-substituent is an alkoxyl group, a significant amount of brominated-oxidized products is obtained.Monitoring the oxidation reaction by mass spectrometry allowed the characterization of the2-bromoindolylidenemalonate intermediate. A bromonium ion is considered as possible pathwayin the formation of this intermediate. The conformation of unsymmetrical methoxyl and benzyloxylsubstituents was determined from 1H NMR spectra, single-crystal X-ray diffraction and ab initiocalculations.
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