Photoinduced Remote C(sp³)–H Imination Enabled by Vinyl Radical-Mediated 1,5-Hydrogen Atom Transfer

Abstract

A vinyl radical-mediated 1,5-hydrogen atom transfer strategy for remote C(sp3)–H imination under visible-light-induced photochemical metal-free conditions afforded diverse γ-imino alkenes with excellent stereoselectivity. Oxime ester-based bifunctional reagents provided not only nucleophilic alkyl radicals for radical addition reactions with electron-deficient alkynes but also long-lived steady-state imine radicals for trapping alkyl radicals following the intramolecular 1,5-hydrogen migration of unstable olefin radicals.

Photoinduced Difunctionalization of Diazenes Enabled by N–N Radical Coupling

“…On the basis of the above mechanistic exploration and previous reports, − a plausible mechanism is proposed, as outlined in Scheme . The reaction starts with the interaction between compound 1a and excited TXT via a photoinduced EnT process to generate excited species 1a *.…”

“…However, the realization of nitrogen–nitrogen radical cross coupling, particularly cross coupling between nitrogen radicals with different hybridization modes, poses a significant challenge. To investigate the assumption on the difunctionalization of diazenes, we employed established benzophenone oxime esters as difunctionalization reagents. These reagents can generate transient radicals and persistent benzophenone imine radicals through energy transfer (EnT) catalysis in a visible light catalytic system, enabling the difunctionalization of different carbon–carbon unsaturated bonds .…”

Recent advances in hydrogen atom transfer induced C(sp3)–H functionalizations initiated by radical addition to alkynes

“…Within this context, in 2023, Xia, Pan and co-workers disclosed remote C(sp 3 )–H imination via the addition of benzophenone oxime esters to alkynes (Scheme 29). 60 Serving as a bifunctional reagent, 79 initially underwent photoinduced energy transfer (EnT) from the excited photocatalyst, then homolytic cleavage of the weak N–O bond occurred to produce persistent imine radical 29A and transient alkyl radical 29B . After the intermolecular addition of 29B to alkynes and subsequent 1,5-HAT, alkyl radical 29D was formed.…”

Difunctionalization of gem-difluoroalkenes for amination and heteroarylation via metal-free photocatalysis

“…Since 2019, oxime derivatives have been widely used in various reactions, such as decarboxylative functionalization of aryl and alkyl carboxylic acids, 23 decarboxylative imination, 24,25 decarboxylative fluorosulfonylation of aryl and alkyl carboxylic acids 26,27 and dual functionalization of various structures. 28–34 These reactions involve the generation of N - and O -centered radicals through energy-transfer (EnT) in the presence of suitable photocatalysts with high triplet excited state energy and appropriate light sources. Based on the previous work from our group on functionalization of gem -difluoroalkenes and heteroaryl carboxylic oxime esters, 12,27 we attempted to utilize readily available oxime derivatives to provide imino and heteroaryl radicals for amination and heteroarylation of gem -difluoroalkenes simultaneously (Scheme 1b).…”