Dedicated to Professor Franziska Schoenebeck on the occasion of her being awarded
the 2025 Women in Chemistry Award.
Dearomative hydroboration of arenes using nucleophilic boryl radicals provides a powerful
strategy for converting flat, abundant arenes into valuable, three-dimensional organoboron
architectures. While such reactions are well established for electron-deficient arenes,
the analogous transformation of electron-rich heteroarenes remains challenging due
to a polarity mismatch. Herein, we report a photocatalytic approach that enables the
regioselective, dearomative hydroboration of both electron-rich and electron-deficient
indoles and benzofurans using N-heterocyclic carbene boranes. Density functional theory calculations indicate that
the C2 addition of the boryl radical is kinetically favored over the C3 addition,
and that the addition step becomes irreversible due to a subsequent, low-barrier hydrogen-atom-transfer
event.
Keywords
Photocatalysis - Boryl radical - Hydroboration - Dearomatization - Organoboron -
N-heterocyclic carbene borane
