Date of Award
1992
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
Aspects of the photochemistry of N-acylindoles in which the indole nitrogen is part of an amide or urethane group have been studied. It has been found that the chemical fate of the N-acylindole excited state can be controlled by appropriate choice of wavelength, solvent, concentration, excited state multiplicity and structure of the acyl substituent.;Irradiation of N-benzoylindole or N-ethoxycarbonylindole with ultra-violet light in the presence of cyclopentene gives a mixture of (2+2) cycloadducts and rearranged photo-Fries products. The quantum yields of formation of the photo-Fries products were found to be wavelength dependent and, especially in the case of N-benzoylindole, highly solvent dependent. The quantum yields of formation of the cycloaddition products were found to be solvent dependent as well. These features allow for the complete control of product ratios.;Direct irradiation of N-ethoxycarbonylindole, N-acetylindole, N-benzyloxycarbonylindole and N-vinyloxycarbonylindole with Pyrex filtered ultra-violet light was found to give moderate yields of dimerization products. Yields were vastly improved by increasing N-acylindole concentration and by using acetophenone as a triplet sensitizer. The reaction was found to be regioselective.;The (2+2) photocycloaddition reactions of N-ethoxycarbonylindole and also of cyclopentenone with {dollar}\omega{dollar}-hydroxy-1-alkenes were examined. In the case of N-ethoxycarbonylindole, cycloaddition quantum efficiency was found to be significantly reduced when the alkene possessed the remote hydroxyl substituted. For cyclopentenone, increasing the number of methylene linkages between the alkene and hydroxyl group was found to increase the quantum efficiency of (2+2) photocycloaddition when the reaction was performed in hexane but not in methanol. These results have been interpreted in terms of hydrogen bonding of the remote hydroxyl function in the intermediate 1,4-biradical.;The formation of intramolecular photoadducts from N-alkenoylindoles (eg. condensation of indole with 4-pentenoic acid) has been investigated. Variation of the distance between the alkene and indole substrate using methylene linkages of various lengths indicates that closure to a six-membered ring (i.e. 2 methylene groups) is most efficient. Ethanolysis and N-acylation of the intramolecular adduct renders the corresponding head-to-head (2+2) cycloadduct, a minor or unattainable product of the analogous intermolecular photocycloaddition of N-acetylindole and ethyl 4-pentenoate. Use of an N-urethane linkage (i.e. an N-alkenyloxycarbonylindole) renders the N-substituted indole completely incapable of intramolecular photochemical cycloaddition. Molecular modelling and variable temperature n.m.r. techniques were used to show that this arises from conformational limitations inherent in the urethane linkage which limit interaction of the alkene with the 2,3-position of the indole.
Recommended Citation
Oldroyd, David L., "Intermolecular And Intramolecular Photocycloaddition Reactions Of Cyclopentenone And N-acylindoles" (1992). Digitized Theses. 2160.
https://ir.lib.uwo.ca/digitizedtheses/2160