Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Part I. Ultra-violet irradiation of N-acylindoles in the presence of alkenes results in the formation of 2+2 photocycloadducts containing a cyclobutane ring derived from the bonding of the alkene termini to the 2 and 3-positions of the indole. The reaction proceeds via the triplet excited state of the N-acylindole with a quantum yield of product formation which is much less than that of the quantum yield for intersystem crossing. The reaction's inefficiency is explained by the existence of 1,4-biradical intermediates which can undergo cleavage to yield ground state starting materials in competition with ring closure to give the observed photocycloadducts. Part I of this thesis describes evidence for the existence of the 1,4-biradical intermediates and for their structures. The cycloadducts obtained from N-acylindoles and flexible alkenes show mixed stereochemistries which is indicative of a 1,4-biradical intermediate. The structures of the products formed by rearrangement of the biradical generated from the photocylcoaddition of N-benzoylindole with vinylcyclopropane indicate that the initial site of bonding between the indole and the alkene is at the 2-position of the indole moiety. The products observed from this reaction along with those from the photocycloaddition of N-benzoylindole with 1,6-heptadiene allow the lifetimes of the biradicals to be "clocked" at approximately 100 ns.;Part II. The possible factors governing the regioselectivity of the 2+2 photocycloaddition reaction of enones with alkenes are discussed. A study was conducted aimed at determining whether the regioselectivity of the photochemical reaction between cyclopentenone and ethyl vinyl ether is governed by the relative rates of formation of the isomeric 1,4-biradical intermediates or by the proportions with which these intermediates partition between cycloadducts and starting materials. A route for the generation of models of the 1,4-biradicals generated in the photocycloaddition reaction of cyclopentenone with ethyl vinyl ether was examined.;The relative rate constants for formation of the 1,4-biradical intermediates in the reaction of cyclopentenone with ethyl vinyl ether were determined by trapping the biradicals with H{dollar}\sb2{dollar}Se. (Abstract shortened by UMI.)



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