Winkelbauer, Joseph
(2021)
Regulating Reactivity and Selectivity of a Dehydro-Diels–Alder Reaction of Vinyl Heteroarenes Informed by Mechanism and Application towards the Synthesis of Photovoltaic Materials.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Ring-fused heteroarenes are present in numerous natural products, FDA approved drugs, agrochemicals, and recently, organic solar cells able to achieve record breaking power conversion efficiencies. Access to these valuable compounds relies primarily on synthesis with dearomative cycloadditions of heteroarenes emerging as an efficient strategy. Many of these reactions require forceful conditions that utilize catalysts, acids and bases, or high temperatures to effect dearomatization. We have developed an intramolecular dearomative didehydro-Diels–Alder (DDDA) reaction which proceeds at temperatures as low as 60 °C with mild conditions, free of additives or catalysts. The adduct of the dearomative cycloaddition, which has been isolated and characterized, readily rearomatizes to either an isomerization product by way of a hydrogen migration or an oxidation product by way of a dehydrogenation.
To determine the substrate dependent factors that control the dearomative cycloaddition, kinetic studies were conducted with in situ reaction monitoring by ReactIR and afforded experimental Gibbs free energies of activation which correlated well with DFT calculations to reveal a highly asynchronous, concerted transition state. Aromaticity of the heteroarene, tether composition, and dispersion interactions were identified as substrate dependent factors that affect reactivity, establishing DFT calculations as a predictive tool in determining reactivity.
For the first time, the 1,4-cyclohexadienyl DA adduct was isolated, characterized, and confirmed as the product of the dearomative cycloaddition with divergent reactivity from the adduct leading to formation of either oxidation or isomerization products. These divergent mechanisms were investigated, and product selectivity was enhanced with control over the reaction parameters. Experiments utilizing deuterium oxide or increased exposure to air revealed the isomerization products were formed by an intermolecular, ionic proton transfer, while oxidation products were formed by an oxygen promoted dehydrogenation. Selectivity for either product was enhanced through reaction parameters such as temperature, solvent polarity, concentration, atmosphere, and additives.
Insight into the mechanisms of dearomatization and product formation allowed us to enhance the reactivity and product selectivity of the dearomative DDDA reaction for vinyl heteroarenes which was then applied towards the synthesis of ladder-type heteroarenes for organic photovoltaic materials. We expect these mechanistic findings to lend insight into other dearomative processes in the future.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
8 October 2021 |
| Date Type: |
Publication |
| Defense Date: |
5 May 2021 |
| Approval Date: |
8 October 2021 |
| Submission Date: |
12 May 2021 |
| Access Restriction: |
1 year -- Restrict access to University of Pittsburgh for a period of 1 year. |
| Number of Pages: |
429 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Chemistry |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Diels Alder Dearomative Heteroarene Kinetic ReactIR Reactivity activation energy gibbs free transition state mechanism computational brummond rate product selectivity |
| Date Deposited: |
08 Oct 2021 19:50 |
| Last Modified: |
08 Oct 2022 05:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/41075 |
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