Metal-free cross-coupling of π-conjugated triazenes with unactivated arenes via photoactivation

Abstract

A metal-free synthesis of biaryl compounds was achieved under photo-irradiation, which represents a milder alternative for cross-coupling reactions.

π‐Conjugated Triazenes and Nitriles: Simple Photoinduced Synthesis of Anilides Using Mild and Metal‐Free Conditions

“…Considering our recently published work, the data obtained, and the trends observed, we propose a reaction mechanism, as illustrated in Scheme . During the initial step, triazene 3 a gets protonated by TFA, this protonated triazene subsequently undergoes photoisomerization from the ( E ) isomer (5‐ E ) to the ( Z ) isomer (5‐ Z ).…”

“…In our continued effort to develop greener alternatives for carbon‐carbon and carbon‐heteroatom bond forming reactions, we have achieved and reported mild methods that produce aldehydes, ketones, ethers, thioethers, allenols, miscellaneous allylic compounds, and biaryls . More recently, we discovered a mild photoinduced cross‐coupling reaction of π‐conjugated triazenes with unactivated arenes . This aryl‐aryl cross‐coupling served as the foundation for the design of a milder alternative for more efficient synthesis of amides, reported in this paper (Scheme , eq.…”

“…5). Our recent report demonstrated that π‐conjugated triazenes can be easily photoactivated in the presence of a Brønsted acid . At that time, tert ‐butylimidazolium tetrafluoroborate ( 1 ) was identified as the best N‐ heterocyclic carbene precursor to enhance the reactivity of triazenes.…”

“…With the optimal conditions established, we explored the overall potential and scope of our new synthetic transformation. For this purpose, we prepared several triazenes, following our previously established methodology . Yields were excellent and included: electron‐rich, electron‐poor, sterically hindered substrates, and halide‐containing triazenes (Scheme ).…”

“…The first test involved the biaryl‐containing amide compound 11 , which has been shown to inhibit interleukin‐2 cytokine, suppressing the immunological processes of cells . To achieve the synthesis of 11 , we took advantage of our recent report that utilized a mild strategy to photochemically promote aryl‐aryl cross‐coupling reactions of π‐conjugated triazenes with arenes, in a tandem process with this amide bond formation reaction (Scheme ). First, triazene 3 r was synthesized in 63% yield by the coupling of di tert ‐butylimidazolium tetrafluoroborate 1 with 1,4‐diazidobenzene 2 r , using potassium tert ‐butoxide as a base (Scheme , eq.…”