Reductive transformations of nitroarenes catalyzed by P(III)/P(V)=O redox cycling
Author(s)
Nykaza, Trevor V.(Trevor Vincent)
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Massachusetts Institute of Technology. Department of Chemistry.
Advisor
Alexander T. Radosevich.
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Nitroaromatics are widely available synthetic building blocks which present a strategical opportunity to serve as direct precursors to nitrogen-containing molecules of increasing complexity and worth through reductive/deoxygenative methods. Trivalent phosphorus compounds are valuable stoichiometric reagents for a range of reductive O-atom transfer reactions involving the conversion of R₃P[superscript III] to R₃P[superscript V]=O (including nitroarene deoxygenation), but can suffer from instability, pyrophoricity, and difficulty of removal during purification for both the phosphine and the generated phosphine oxide. Having the ability to start with a bench-stable phosphine oxide--which most often is regarded as a waste by-product--and repeatedly generate an active phosphine species in situ for catalytic reaction chemistry is a motivating concept with potentially practical benefits. With the incorporation of a hydrosilane reductant, it is demonstrated that a small-ring cyclic phosphine oxide can be quickly reduced in situ to catalyze the intramolecular cyclization of o-functionalized nitrobenzene derivatives to produce nitrogen-containing heterocycles (2H-indazoles, 2H-benzotriazoles, carbazoles, indoles, and benzimidazoles), as well as the intermolecular C-N cross coupling of nitroarenes with boronic acids through exhaustive nitro deoxygenation via P[superscript III]/P[superscript V]=O catalysis. The work herein not only describes the discovery of new organocatalytic methods founded on the use of a designer, small-ring phosphine oxide (pre)catalyst (1,2,2,3,4,4-hexamethylphosphetane 1-oxide) for the reductive transformations of nitroarenes, but also details investigations into the reaction mechanism for both reductive cyclization and C-N coupling reactions.
Description
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2020 Cataloged from the PDF of thesis. "February 2020." Includes bibliographical references.
Date issued
2020Department
Massachusetts Institute of Technology. Department of ChemistryPublisher
Massachusetts Institute of Technology
Keywords
Chemistry.