Iron‐Photocatalyzed Anti‐Markovnikov Hydrochlorination of Alkenes Based on Ligand‐to‐Metal Charge Transfer

Ligand‐to‐metal charge transfer (LMCT) photocatalysis using simple, inexpensive, and environmentally benign iron salts has attracted increasing attention owing to its potential to expand the landscape of photocatalysis beyond conventional intermolecular single‐electron transfer‐based photoredox systems; however, its synthetic utility and applications remain underexplored. Herein, a selective anti‐Markovnikov hydrochlorination of alkenes with hydrochloric acid, a challenging transformation in organic synthesis, enabled by a combination of FeCl 3 ‐mediated LMCT photocatalysis and hydrogen atom transfer (HAT) catalysis is reported. Monosubstituted benzenethiols are employed as electronically tunable HAT catalysts enabling precise control over radical reactivity. The results of experimental and theoretical investigations reveal a strong correlation between the reaction efficiency, the activation free energy of the HAT step, and electronic properties of the benzenethiol catalysts. The obtained mechanistic insights not only rationalize the observed reactivity but also establish a predictive framework for future HAT catalyst design.