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Photoredox Strategies for Asymmetric Catalysis and Determination of Open-Shell Hammett Substituent Constants /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Photoredox Strategies for Asymmetric Catalysis and Determination of Open-Shell Hammett Substituent Constants /Eve Yuanwei Xu.
Author:	Xu, Eve Yuanwei,
Description:	1 electronic resource (442 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 87-04, Section: B.
Notes:	Advisors: Knowles, Robert R. Committee members: Hyster, Todd; Stache, Erin E.; Roque, Jose.
Contained By:	Dissertations Abstracts International87-04B.
Subject:	Organic chemistry.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=32170154
ISBN:	9798297600102

Photoredox Strategies for Asymmetric Catalysis and Determination of Open-Shell Hammett Substituent Constants /
Xu, Eve Yuanwei,

Photoredox Strategies for Asymmetric Catalysis and Determination of Open-Shell Hammett Substituent Constants /Eve Yuanwei Xu. - 1 electronic resource (442 pages)

Source: Dissertations Abstracts International, Volume: 87-04, Section: B.

Free radicals are typically viewed as transient and highly reactive species. Precise modulation of their reactivity continues to be a fundamental challenge in organic synthesis. Meanwhile, advancements in photoredox catalysis have enabled the efficient and selective generation of a wide range of radical intermediates, broadening their utility in synthetic methodologies. This dissertation broadly examines the reactivity and properties of organic radicals, focusing particularly on species formed under photoredox conditions.Chapter 1 presents a detailed mechanistic study of enantioselective hydroamination of alkenes with sulfonamides enabled by proton-coupled electron transfer (PCET). The study suggests that the basis for asymmetric induction arises from attractive noncovalent interactions within a post-PCET H-bonding complex formed between a neutral sulfonamidyl radical intermediate and a chiral phosphoric acid catalyst.Chapter 2 describes the development of a light-driven method for enantioselective contrathermodynamic olefin isomerization. Sequential oxidation and deprotonation of a tetra-substituted enol ether produces an allyl radical, which is captured by a Cr(II) cocatalyst bearing a chiral bi-oxazoline (BiOX) ligand. Subsequent regio- and enantioselective protodemetalation of the resulting Cr(III) allyl complex by methanol affords the enantioenriched terminal olefin product, achieving selectivity up to 95:5 er.Chapter 3 outlines a combined experimental and computational approach to determine Hammett constants for open-shell substituents, based on changes in nitrile vibrational frequencies (ν(C≡N)). By coupling pulse radiolysis with time-resolved infrared spectroscopy (PR-TRIR), ν(C≡N) IR bands were measured for 30 para- and meta-substituted benzonitriles bearing C-, N-, and S-centered radicals. A linear scaling relationship was established between the experimental data and values obtained from DFT calculations. Using computed values, two distinct Hammett constants, σm and σp+, were derived for a series of C-, N-, O-, S-, Si-, and B-centered radicals.

English

ISBN: 9798297600102Subjects--Topical Terms:

708640
Organic chemistry.
Subjects--Index Terms:

Asymmetric catalysis

Photoredox Strategies for Asymmetric Catalysis and Determination of Open-Shell Hammett Substituent Constants /
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520 $a Free radicals are typically viewed as transient and highly reactive species. Precise modulation of their reactivity continues to be a fundamental challenge in organic synthesis. Meanwhile, advancements in photoredox catalysis have enabled the efficient and selective generation of a wide range of radical intermediates, broadening their utility in synthetic methodologies. This dissertation broadly examines the reactivity and properties of organic radicals, focusing particularly on species formed under photoredox conditions.Chapter 1 presents a detailed mechanistic study of enantioselective hydroamination of alkenes with sulfonamides enabled by proton-coupled electron transfer (PCET). The study suggests that the basis for asymmetric induction arises from attractive noncovalent interactions within a post-PCET H-bonding complex formed between a neutral sulfonamidyl radical intermediate and a chiral phosphoric acid catalyst.Chapter 2 describes the development of a light-driven method for enantioselective contrathermodynamic olefin isomerization. Sequential oxidation and deprotonation of a tetra-substituted enol ether produces an allyl radical, which is captured by a Cr(II) cocatalyst bearing a chiral bi-oxazoline (BiOX) ligand. Subsequent regio- and enantioselective protodemetalation of the resulting Cr(III) allyl complex by methanol affords the enantioenriched terminal olefin product, achieving selectivity up to 95:5 er.Chapter 3 outlines a combined experimental and computational approach to determine Hammett constants for open-shell substituents, based on changes in nitrile vibrational frequencies (ν(C≡N)). By coupling pulse radiolysis with time-resolved infrared spectroscopy (PR-TRIR), ν(C≡N) IR bands were measured for 30 para- and meta-substituted benzonitriles bearing C-, N-, and S-centered radicals. A linear scaling relationship was established between the experimental data and values obtained from DFT calculations. Using computed values, two distinct Hammett constants, σm and σp+, were derived for a series of C-, N-, O-, S-, Si-, and B-centered radicals.
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653 $a Radicals
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