| The ability of a series of nitrogen-substituents to activate the cycloaddition photochemistry of indoles has been examined; the N-substituents were chosen in order to enable their removal following cycloaddition under mild neutral, acidic or basic conditions. N-substituted indoles, 17, 12 and 104c-g, were prepared in which the N-substituent is COPh, CO;The silylethoxycarbonyl group of photoadducts derived from 104c can be removed by treatment of the adduct with fluoride ion in dichloromethane, the tert-butyloxycarbonyl group of adducts derived from 104e by treatment with trifluoroacetic acid at room temperature; the benzyloxycarbonyl group of adducts derived from 104g by hydrogenolysis, and the cyanoethoxycarbonyl group of adducts derived from 104d by treatment with aqueous alcoholic carbonate at room temperature.;The quantum yield of intersystem crossing for carboethoxyindole (CEI), 12, was determined to be 0.32. It is concluded that the proportion of the biradical intermediates proceeding to the adducts for the CEI cycloaddition is circa 2% and that circa 98% go back to the starting materials. In contrast, with NBI 16% of the biradicals proceed to adduct and 84% revert to starting materials.;The N-acylindoles 12, 13 (N-acetylindole), 17, and 104c.f.g were found to yield cyclobutane dimers when irradiated with ultra-violet light. Attempted generation of the N-unsubstituted indole dimers from the photodimers by removal of the N-substituents was unsuccessful and led to decomposition to indole and N-acylindole. This implies that the N-unsubstituted indole dimers are not isolable species.;A dynamic nmr study revealed that the N-acylindoles and their cycloadducts with cyclopentene exist as two slowly interconverting conformers in solution and that the photodimers exist as three slowly interconverting conformers. These conformers arise from the possible orientations of the amide carbonyl present in these compounds.;Intramolecular photocycloaddition of N-carboxyindole anhydride (NCIA) has been found to give two intramolecular cycloadducts. The structure of one of the intramolecular photocycloadducts was determined by conversion to the major intermolecular photodimer obtained from N-ethoxycarbonylindole.;The results from the oxidation of the indolines 107 and 108, obtained from deprotection of N-substituents from the photocycloadducts of the N-acylindoles with cyclopentene, indicate that the desired indole derivative 166 was formed by the Pd/C dehydrogenation. (Abstract shortened by UMI.). |
