Radical‐Based C−C Bond‐Forming Processes Enabled by the Photoexcitation of 4‐Alkyl‐1,4‐dihydropyridines

Abstract

We report herein that 4‐alkyl‐1,4‐dihydropyridines (alkyl‐DHPs) can directly reach an electronically excited state upon light absorption and trigger the generation of C(sp3)‐centered radicals without the need for an external photocatalyst. Selective excitation with a violet‐light‐emitting diode turns alkyl‐DHPs into strong reducing agents that can activate reagents through single‐electron transfer manifolds while undergoing homolytic cleavage to generate radicals. We used this photochemical dual‐reactivity profile to trigger radical‐based carbon–carbon bond‐forming processes, including nickel‐catalyzed cross‐coupling reactions.

Alkyl‐C‐C‐Bindungsbildung durch Nickel/Photoredox‐Kreuzkupplung

“…Die zweite Arbeitsgruppe setzte anstelle der Base den oxidativeren 4CzIPN-Photokatalysator 4 ein (Abbildung 1). [57] Saccharid-derivatisierte DHPs kçnnen in dem Ni/Photoredox-Kreuzkupplungszyklus auch zur Bildung von invertierten C-Arylglycosiden, wie 53,v erwendet werden (Schema 4B).…”

Synthesis of Reversed C‐Acyl Glycosides through Ni/Photoredox Dual Catalysis

“…[17] These processes are governed by a single-electron transmetalation pathway, with an inherent low activation energy barrier favoring C sp3 -hybridized nucleophiles. [18] In this context, we explored 1,4-dihydropyridines (1,4-DHPs) [19] as glycosyl-based radical precursors. These coupling partners are bench stable and can be prepared from inexpensive starting materials.…”

“…These coupling partners are bench stable and can be prepared from inexpensive starting materials. [19c] Although 1,4-DHPs stem from the corresponding C-formyl glycosides, they are of immense synthetic value as they have low oxidation potentials and thus are amenable for fragmentation using inexpensive organic photocatalysts in lieu of stoichiometric oxidants. [19c] To address the demands associated with the synthesis of non-anomeric Cacyl glycosides, we investigated the feasibility of a crosscoupling reaction of in situ activated carboxylic acids [20] with glycosyl based DHPs in an attempt to access such challenging structural motifs.…”

Catalyst‐Free Deaminative Functionalizations of Primary Amines by Photoinduced Single‐Electron Transfer

“…[6] These strategies have enabled the development of abroad range of radical transformations that proceed through visible light-mediated PET under catalyst-free conditions.However, such reactions are typically limited to the generation of perfluoroalkyl or stabilized alkyl radicals. [11] We sought an alternative functional group that could act as av ersatile photoactive handle for catalyst-free generation of non-stabilized carbon-centered radicals.O ne possibility was Katritzky N-alkylpyridinium salts 1,w hich are easily prepared from primary amines 2 by reaction with 2,4,6-triphenylpyrylium 3,a re air and moisture stable,a nd allow selective deaminative transformations of abundant amino groups (Scheme 1A). [11] We sought an alternative functional group that could act as av ersatile photoactive handle for catalyst-free generation of non-stabilized carbon-centered radicals.O ne possibility was Katritzky N-alkylpyridinium salts 1,w hich are easily prepared from primary amines 2 by reaction with 2,4,6-triphenylpyrylium 3,a re air and moisture stable,a nd allow selective deaminative transformations of abundant amino groups (Scheme 1A).…”