Date of Graduation

12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor/Mentor

McIntosh, Matt

Committee Member

Zheng, Nan

Second Committee Member

Kilyanek, Stefan

Third Committee Member

Striegler, Susanne

Keywords

Breslow Intermediate; NHC; Pyridine; Radical Chemistry

Abstract

This work delves into the reactivity of nucleophilic N-heterocyclic carbenes (NHCs) and their ability to form electron-rich alkene intermediates, which can undergo various chemical transformations depending on the nature of the electrophile. Initial reports by Hahn disclosed the NHC promoted radical nature of electron-rich N,N’-benzyltetraazafulvalenes, which led to 2,2’- biimidazoles. We found that N-aryl substituted pyridinium salts also underwent rapid a similar NHC promoted dimerization when exposed to a base, producing 2,2’-bipyridyls. This is likely due to the adept radical nature of the bipyridinylidene intermediate for C-Naryl bond scission. We have also uncovered an unprecedented C-N bond scission of Breslow-like intermediates of 4- or 3- substituted pyridine motifs. This exhibited a distinct reaction pattern that led to 2-acyl pyridines through a radical disproportion pathway. Contrary to the widely reported Minisci-type reactions employing transition metals and harsh oxidants, this novel pathway provides a milder approach to accessing 2-ketopyridines whose derivatives are found in biologically and industrially relevant compounds. Additionally, other unique behaviors of pyridine-derived Breslow intermediates were observed. NHC catalyzed benzoin condensation occurred in some cases leading to benzoin condensation products. Moreover, electron-poor aldehydes were reduced to primary alcohols, indicating the role of the Breslow intermediate also behaving as a single electron transfer (SET) reducing agent.

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