Abstract
<jats:p>Among possible arylation strategies, a radical pathway appears to be a promising alternative to transition-metal catalyzed cross-coupling reactions. Aryl boronic acids are regarded as ideal precursors of aryl radicals due to their broad commercial availability and low toxicity. Yet, extremely high oxidation potentials and unfavourable thermodynamics of a carbon-boron bond cleavage effectively limit their applicability as aryl radical reservoir in radical-type transformations. To address this challenge, we developed an unprecedented, organophotocatalytic arylation methodology that is based on the transformation of hardly oxidizable aryl boronic acids in situ into photoresponsive diaryliodonium salts via covalent activation. These species are much more prone to undergo a photoreduction via single-electron transfer with a cost-effective organophotocatalyst – Eosin Y (18 $ / 1 g), followed by carbon-iodine bond cleavage, eventually giving rise to aryl radicals. Our redox inversion strategy demonstrates broad functional group tolerance, accommodating a variety of aryl boronic acids and N-heterocycles, including late-stage modification of several complex bioactive molecules. Our studies also highlight the critical role of a solvent (HFIP) in facilitating this new reaction manifold of covalent activation of aryl organoborons, as it effectively forms hydrogen bonding networks that govern the overall reactivity of reactants, intermediates, as well as the photocatalyst. This work presents a new synthetic concept for the in situ activation of a carbon-boron bond within aryl boronic acids, offering a mild, highly selective and versatile strategy towards functionalized nitrogen-containing heterocycles, thereby enabling broader applications in synthetic organic chemistry.</jats:p>