Previous work from our laboratory has been concerned with investigating
the photochemical reactivity of tetrahydro-1,4-naphthalenedione and tetrahydronaphthoquinol systems, both in the solid state and in solution. The fascinating results obtained prompted us to extend the studies to the analogous tetrahydro-1,4-anthracenediones, tetrahydro-5,12-naphthacenediones and tetrahydroanthraquinol systems. Tetrahydro-1,4-anthracenedione is expected to undergo bis-enolization with extreme ease, and therefore its preparation requires mild and neutral conditions.
These compounds were prepared by Diels-Alder reaction between o-quinodimethane and p-benzoquinone and other p-substituted quinones o-Quinodimethane was generated in situ by sulphur dioxide extrusion from 3,6-dihydrobenzo[b]oxathiin-2-oxide.
The photochemistry of the tetrahydro-1,4-anthracenediones, tetra-hydro-5,12-naphthalenedione and tetrahydroanthraquinols has been investigated both in the solid state and solution. The effect of the solid state medium on the photoreactivity, compared to the solution, is significant; the nature and/or the number of the photoproducts formed in the solid state is generally different from the results obtained in solution. These differences have been explained on the basis of the crystal and molecular structures of the reactants. Special steric effects, which may impede the photochemical reactions in the solid state have been identified. The values of the geometric parameters (d, r and A) for hydrogen atom abstraction are found to be similar to those observed in earlier studies by Scheffer et al.
It has been found that the o-quinodimethane/2,3-dimethyl-l,4-naphthoquinone adduct affords, via β-hydrogen atom abstraction and closure of the resulting 1,3-biradical, a cyclopropanol. The cyclopro-panol itself undergoes photolysis initiated by a novel ring opening process. Irradiation of crystals of the adduct does not result in any cyclopropanol. The reasons for the non-reactivity of the Diels-Alder adduct in the solid state have been suggested to be due to the non-bonded steric interactions between the lattice neighbors as shown by the X-ray crystal structure.
The photorearrangement of one substrate, namely 2,3,4a,9a-tetra-methyl-4a,9a,9,10-tetrahydro-1,4-anthracenedione is found to be controlled
by the temperature, multiplicity, and phase of the reaction. By carrying out the reaction at or above room temperature or in the presence
of a sensitizer or in the crystalline state, the reaction can be forced in one direction. Lowering the photolysis temperature causes the formation of another product. The nature of the photoproduct is independent
of the temperature in the crystalline state. The results have been interpreted in terms of a required ring inversion which is needed for the formation of the low temperature photoproduct (see Scheme 44). The ring inversion is not allowed in the solid state. / Science, Faculty of / Chemistry, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/26954 |
| Date | January 1987 |
| Creators | Askari, Syed Hasan |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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