title: Aromatic bromination versus oxidation of indolylmalonates by bromine.
abstract: The reactions of 5-substituted indolylmalonates (2a-e), carrying an electron-withdrawing group at the N(1) position, with bromine in CCl(4) or AcOH are reported. These substrates undergo oxidation in competition with the well-known aromatic bromination. Under the two sets of conditions, with parent indolylmalonate (2a), chemospecific oxidation is observed, whereas with 5-hydroxyindolylmalonate (2c), bromination at the 4- and 6-position is the dominating reaction. Investigation of the products composition of several 5-substituted indolylmalonates revealed the following trend: with a 5-substituted electron-withdrawing group like fluorine, the indolylmalonate undergoes oxidation rather than bromination. In contrast, with a 5-substituted electron-donating group, like a hydroxyl group, the ring bromination occurs preferentially over the oxidation. When the 5-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 the 2-bromoindolylidenemalonate intermediate. A bromonium ion is considered as possible pathway in the formation of this intermediate. The conformation of unsymmetrical methoxyl and benzyloxyl substituents was determined from (1)H NMR spectra, single-crystal X-ray diffraction and ab initio calculations.
authors.affiliation: Departamento de Química, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado 14-740, México D. F. 07000, Mexico.
authors.forename: Martha S
authors.initials: MS
authors.lastname: Morales-Ríos
authors.forename: Norma F
authors.initials: NF
authors.lastname: Santos-Sánchez
authors.forename: Oscar R
authors.initials: OR
authors.lastname: Suárez-Castillo
authors.forename: Pedro
authors.initials: P
authors.lastname: Joseph-Nathan