Redox‐Active Guanidines in Proton‐Coupled Electron‐Transfer Reactions: Real Alternatives to Benzoquinones?

Guanidino‐functionalized aromatics (GFAs) are readily available, stable organic redox‐active compounds. In this work we apply one particular GFA compound, 1,2,4,5‐tetrakis(tetramethylguanidino)benzene, in its oxidized form in a variety of oxidation/oxidative coupling reactions to demonstrate the scope of its proton‐coupled electron transfer (PCET) reactivity. Addition of an excess of acid boosts its oxidation power, enabling the oxidative coupling of substrates with redox potentials of at least +0.77 V vs. Fc(+)/Fc. The green recyclability by catalytic re‐oxidation with dioxygen is also shown. Finally, a direct comparison indicates that GFAs are real alternatives to toxic halo‐ or cyano‐substituted benzoquinones.