| dc.contributor.author | Kumarasamy, Elango | |
| dc.description.abstract | Photochemical transformations are unique strategy in synthesis that enables us to
access complex and structurally diverse organic scaffolds. However, the challenges in controlling
the excited-state to perform stereoselective reactions left this method under-utilized. This
dissertation describes a novel strategy that employs atropisomeric chromophores to perform
stereospecific phototransformations. The success of this strategy is well established in thermal
chemistry but not comprehensively investigated in photochemical transformations. This research
largely relies on rotamer control in the ground state (NEER principle) wherein the axial chirality in
the starting material was transferred to point chirality in the products upon excitation.
The chapter 1 describes the principle differences between the asymmetric thermal and
asymmetric photochemical reactions. Further, a survey of methodologies developed towards
asymmetric phototransformations and their outcomes are described. A brief introduction about
the atropisomeric systems in thermal chemistry and the preliminary investigations in
phototransformations are also provided.
In chapter 2, enantiospecific disrotatory 4π-ring closure of atropisomeric 2-pyridones
were investigated. The differential axial chirality designed (sterics and H-bonding units) displayed
distinct temperature and solvent dependency on the enantiospecificity of the reaction. Eyring plot
was computed to calculate the differential activation enthalpy and entropy for the reaction. Also,
the course of phototransformation was followed through single-crystal XRD to decipher the
preferred mode of cyclization for a given isomer of 2-pyridones. The high-pressure racemization
and photoreaction study revealed that pressure provided stable chiral axis even at elevated
temperature resulting in higher enantiomeric excess (ee) in the photoproduct.
The chapters 3-5 describe the [2+2]-photocycloaddition of atropisomeric enamide,
maleimide and imine derivatives. The design features on these molecules allowed us to perform
complementary reactions that are not observed in the literature. These modifications were
significant improvement to “axial to point chiral” strategy that improves the versatility of the
photoreactions. For example switching of the excited state in enamides, continuous flow visibleiv
light photocatalysis of maleimides and unusual photocycloaddition of stabilized imines are notable
features.
This dissertation encompasses detailed studies on the mechanism, scope and
photophysical studies on new atropisomeric chromophores such as 2-pyridones, enamides,
maleimides and imine derivatives that provides excellent avenue to access chirally enriched
building blocks. | en_US |
| dc.publisher | North Dakota State University | en_US |
| dc.rights | NDSU Policy 190.6.2 | |
| dc.title | Stereospecific Phototransformations of Atropisomeric Chromophores | en_US |
| dc.type | Dissertation | en_US |
| dc.date.accessioned | 2018-02-14T21:11:04Z | |
| dc.date.available | 2018-02-14T21:11:04Z | |
| dc.date.issued | 2014 | |
| dc.identifier.uri | https://hdl.handle.net/10365/27553 | |
| dc.description.sponsorship | NSF-ND EPSCoR (Doctoral Dissertation Fellowship) | en_US |
| dc.description.sponsorship | Department of Chemistry and Biochemistry. North Dakota State University | en_US |
| 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 | Jayaraman, Sivaguru | |
