- Library Home /
- Search Collections /
- Open Collections /
- Browse Collections /
- UBC Theses and Dissertations /
- Photochemistry of Diels-Alder adducts
Open Collections
UBC Theses and Dissertations
UBC Theses and Dissertations
Photochemistry of Diels-Alder adducts Gayler, Rudolf Erich
Abstract
The photochemistry of a variety of Diels-Alder adducts of general structure I has been investigated. The adducts chosen for study were those formed between the dienophiles p-benzoquinone, 1,4-naphthoquinone, and duroquinone and the dienes 2,3-dimethylbutadiene, trans,trans-2,4-hexadiene, 2-methylbutadiene, and 1,3-pentadiene. Three substituent-dependent photochemical reaction types were observed: (1) For adducts with C₅α and/or C₈α methyl groups, γ-hydrogen abstraction was preferred and led to the novel ring system II. (2) For adducts lacking these γ-hydrogen atoms, an unusual new reaction course prevailed. This consisted of β-hydrogen atom abstraction from C₅ (or equivalently C₈) to give the diradical III. Closure of this diallylic diradical in three of the possible four ways (1,6-bonding, 3,8-bonding and 3,6-bonding) and subsequent ketonization gave the observed products of general structure IV, V and VI respectively, although not all three products were observed in each case. The relative amounts of these products were strongly solvent dependent. A methyl group at C₆ directed the β -hydrogen abstraction to the C₈ position in accord with expectations based on radical stability. This same overall reactivity obtained for the corresponding naphthoquinone Diels-Alder adducts. (3) Finally, for the duroquinone-2,3-dimethylbutadiene adduct an unusual cyclobutanone-con- taining photoproduct VII was observed in addition to those resulting from β -hydrogen abstraction. Based on deuterium labeling studies, this product was suggested to arise via direct C₈ hydrogen abstraction by the C₃ enone carbon atom followed by 2,8 bonding. Photoproducts of the type IV,VI and VII undergo novel thermal rearrangements for which mechanisms are proposed. In addition ene-dione VII undergoes a particularly intriguing base-catalyzed rearrangement which is formally the result of a 1,2-carbanionic shift. In summary, the photochemical reactions described demonstrate interesting variations on the familiar γ-hydrogen abstraction process, show the feasibility and preliminary scope of excited state β-hydrogen abstraction processes (heretofore virtually unknown), and appear to provide a general method for the synthesis of tricyclic ring systems of the type II and V which are closely related to certain naturally occurring sesquiterpenes. [See Thesis for Diagrams]
Item Metadata
Title |
Photochemistry of Diels-Alder adducts
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
1973
|
Description |
The photochemistry of a variety of Diels-Alder adducts of general structure I has been investigated. The adducts chosen for study were those formed between the dienophiles p-benzoquinone, 1,4-naphthoquinone, and duroquinone and the dienes 2,3-dimethylbutadiene, trans,trans-2,4-hexadiene, 2-methylbutadiene, and 1,3-pentadiene.
Three substituent-dependent photochemical reaction types were observed: (1) For adducts with C₅α and/or C₈α methyl groups, γ-hydrogen
abstraction was preferred and led to the novel ring system II. (2) For
adducts lacking these γ-hydrogen atoms, an unusual new reaction course
prevailed. This consisted of β-hydrogen atom abstraction from C₅ (or
equivalently C₈) to give the diradical III. Closure of this diallylic
diradical in three of the possible four ways (1,6-bonding, 3,8-bonding
and 3,6-bonding) and subsequent ketonization gave the observed products
of general structure IV, V and VI respectively, although not all three
products were observed in each case. The relative amounts of these
products were strongly solvent dependent. A methyl group at C₆ directed
the β -hydrogen abstraction to the C₈ position in accord with expectations
based on radical stability. This same overall reactivity obtained for the
corresponding naphthoquinone Diels-Alder adducts. (3) Finally, for the
duroquinone-2,3-dimethylbutadiene adduct an unusual cyclobutanone-con-
taining photoproduct VII was observed in addition to those resulting from
β -hydrogen abstraction. Based on deuterium labeling studies, this product
was suggested to arise via direct C₈ hydrogen abstraction by the C₃ enone
carbon atom followed by 2,8 bonding.
Photoproducts of the type IV,VI and VII undergo novel thermal rearrangements for which mechanisms are proposed. In addition ene-dione VII undergoes a particularly intriguing base-catalyzed rearrangement which is formally the result of a 1,2-carbanionic shift.
In summary, the photochemical reactions described demonstrate interesting variations on the familiar γ-hydrogen abstraction process, show the feasibility and preliminary scope of excited state β-hydrogen abstraction processes (heretofore virtually unknown), and appear to provide a general method for the synthesis of tricyclic ring systems of the type II and V which are closely related to certain naturally occurring sesquiterpenes. [See Thesis for Diagrams]
|
Genre | |
Type | |
Language |
eng
|
Date Available |
2011-03-03
|
Provider |
Vancouver : University of British Columbia Library
|
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.
|
DOI |
10.14288/1.0060041
|
URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
|
Campus | |
Scholarly Level |
Graduate
|
Aggregated Source Repository |
DSpace
|
Item Media
Item Citations and Data
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.