Electrochemical Synthesis of Polycyclic N-Heteroaromatics through Cascade Radical Cyclization of Diynes

Abstract

An electrochemical cyclization reaction of easily available urea-tethered diynes has been developed for the synthesis of nitrogendoped polycyclic aromatic hydrocarbons (PAHs). The employment of ferrocene as a mild and selective redox catalyst allows access to a variety of electron-rich PAHs including helicene-like structures without overoxidation. The electrosynthetic method involves an unprecedented amidyl radical cascade cyclization process to form three rings in a single operation.

Electrochemically Enabled Intramolecular Aminooxygenation of Alkynes via Amidyl Radical Cyclization

“…The inferior results obtained using stoichiometric oxidant also highlighted the advantage of our electrochemical method. The alkyne substrates are known to undergo base promoted hydroamidation reaction [7c,10] . For example, propargyl carbamate 30 underwent efficient hydroxide‐promoted ionic cyclization to afford oxazolidinone 32 in 78% yield.…”

Electrochemical Synthesis of Imidazo‐Fused N‐Heteroaromatic Compounds through a C−N Bond‐Forming Radical Cascade

“…Organic electrochemistry is a powerful and attractive tool for organic synthesis because it employs electrons as “reagents” and is tunable in the activation of small molecules to generate reactive intermediates . In this context, few methods have been developed for preparing amidyl radicals via direct or indirect, electrolysis of N−H bearing precursors. Here we report an electrochemical synthesis of imidazo‐fused N‐heteroaromatic compounds through an unprecedented radical C−N bond‐forming cyclization cascade (Scheme b).…”

Electrochemical strategies for C–H functionalization and C–N bond formation

“…Nitrogen-centered radicals have also been harnessed for synthesis of nitrogen-doped polycyclic aromatic hydrocarbons (Scheme 116). [923][924][925] In the presence of ferrocene, the ureatethered diynes 396 underwent efficient radical cyclization to afford a variety of electron-rich polycyclic aromatic hydrocarbons (398). The use of a mild redox catalyst to facilitate the cascade cyclization instead of carrying out direct electrolysis was crucial to avoid overoxidation of the products as the diynes 396 are oxidized at a higher potential than that of products 398.…”