| dc.contributor.author | Ayitou, Anoklase Jean-Luc | |
| dc.description.abstract | Asymmetric photochemical transformations have been under-explored due to the ineffectiveness of conventional methodologies/reagents/catalysts (point chiral auxiliaries and inductors) that were generally employed for thermal reactions. This limitation to use point chiral auxiliaries for asymmetric photochemistry is partly due to the asynchronous behavior of photo-excitation and chiral transfer/induction processes. This dissertation describes a complementary approach to conventional methodologies involving light induced chirality transfer from atropisomeric viz axially chiral molecular reactants (acrylanilides and α-oxoamides) to enantiopure product(s) with point chirality. The study has revealed the importance of rotamers control in the ground state and how it can impact the stereospecificity during light induced excited state reactions leading to enantiopure product(s). Con-rotatory 6π-photocyclization of axially chiral acrylanilides was explored under various reaction conditions. For example, α,β-unsaturated acrylanilides gave the expected 3,4-dihydroquinolin-2- one photoproduct(s) with enantiomeric excess (ee) values > 90% in both direct and triplet sensitized irradiations. On the other hand, the solution phase direct irradiations of α-substituted acrylanilides yielded racemic photoproduct(s) whereas the triplet sensitized reactions led to ee values > 90% in the expected photoproduct(s). By changing the reaction medium from isotropic media to solid state, α-substituted acrylanilides gave photoproducts with ee values as high as 70%. In addition to the effect of the reaction medium and the reactive spin state on the enantioselectivity, preliminary evaluation of the role of Lewis acid(s) and heavy cations (Na+, K+ and Cs+) were explored. The initial observations were quite promising with ee values up to 90% in the photoproducts upon direct irradiation in isotropic media. The photochemical γ-hydrogen abstraction reaction involving axially chiral α-oxoamides leading to β-Lactam photoproducts was investigated. The enantiomeric ratio (e.r.) > 90:10 in the expected β- Lactam photoproducts was found to be dependent on the temperature under which the irradiation was performed. Furthermore, elevated pressure was employed to counter the effect of elevated temperature and slow the rotation around N-C(aryl) chiral axis leading enantioenriched β-Lactam photoproducts. This dissertation details the overall mechanistic rationales and photophysical control studies during the photochemical transformations of atropisomeric acrylanilides and α-oxoamides leading to chirally enriched products. | en_US |
| dc.publisher | North Dakota State University | en_US |
| dc.rights | NDSU Policy 190.6.2 | |
| dc.title | Stereospecific Photochemical Transformations Involving Axially Chiral Acrylanilides and a-Oxoamides | en_US |
| dc.type | Dissertation | en_US |
| dc.date.accessioned | 2017-12-28T19:01:19Z | |
| dc.date.available | 2017-12-28T19:01:19Z | |
| dc.date.issued | 2013 | |
| dc.identifier.uri | https://hdl.handle.net/10365/27134 | |
| dc.rights.uri | https://www.ndsu.edu/fileadmin/policy/190.pdf | |
| ndsu.degree | Doctor of Philosophy (PhD) | en_US |
| ndsu.college | Science and Mathematics | en_US |
| ndsu.department | Chemistry and Biochemistry | en_US |
| ndsu.advisor | Sivaguru, Jayaraman | |
