N-Heterocyclic Electroauxiliaries for the Generation of Alkyl Radicals via C−C Bond Cleavage

by Shahilan Ratnam
Doctoral thesis
Date of Examination:2025-07-03
Date of issue:2025-07-17
Advisor:Dr. Daniel Janßen-Müller
Referee:Dr. Daniel Janßen-Müller
Referee:Prof. Dr. Konrad Koszinowski
Referee:Prof. Dr. Lutz Ackermann
Referee:Prof. Dr. Dr. Lutz Tietze
Referee:Prof. Dr. Johannes C. L. Walker
Referee:Dr. Holm Frauendorf
Persistent Address: http://dx.doi.org/10.53846/goediss-11391

 

 

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Abstract

English

Alkyl radical precursors are essential for a wide variety of photocatalytic and 3d-metal-catalyzed C–C bond forming reactions. In the last decade, neutral organic heterocycles as electroauxiliaries have become reliable tools for alkyl radical formation, such as 4-alkyl Hantzsch esters. In this thesis, 2,2’-biquinoline-derived 2-alkyl-substituted dihydroquinolines were identified and applied for the first time as potent reagents for alkyl radical formation with the aspect of recyclability. The 2-alkyl-substituted dihydroquinolines were successfully applied as radical progenitors of primary, secondary and tertiary alkyl radicals, demonstrated in C–C, C–S, C–N and C–O bond formation reactions. Furthermore, alkyl-substituted dihydropyrimidines (DHPyms), synthesized via the Biginelli reaction, were identified as tunable alternatives to 4-alkyl Hantzsch esters in radical chemistry. The work explores their redox properties, UV/vis absorption, and synthetic potential, demonstrating DHPyms as versatile alkyl radical precursors in C–C, C–N, C–S bond forming reactions. DHPyms with lower oxidation potentials showed enhanced reactivity in Ni/photoredox dual catalytic cross-coupling reactions, outperforming traditional Hantzsch esters.
Keywords: C−C activation; C-C activation; Electroauxiliaries; Radical reactions; Nitrogen heterocycles; Copper; Dihydroquinoline; Biquinoline; Dihydropyrimidine