Iron-catalysed radical difunctionalization of alkenes

Transition metal-catalysed difunctionalization of alkenes enables the rapid construction of complex molecules by converting a flat C(sp ²)-C(sp ²) π-fragment to form a three-dimensional structure with neighbouring sp ³-hybridized carbons and two new C(sp ³)-G bonds (G = carbon, heteroatom, halogen and so on) in a single step. Iron catalysis is attractive because of its lower cost, higher Earth abundance, lower mining carbon footprint and lower toxicity in comparison to traditional transition metal catalysts, but lags behind nickel and palladium in terms of synthetic applications and mechanistic understanding. Here we present an overview of recent reaction development progress and unmet challenges in iron-catalysed difunctionalization reactions, with a focus on three-component radical cross-coupling processes that use commercially available iron salts in combination with readily available ligands. For each case, we highlight the mechanistic insights gained from (in)organic synthesis, computational modelling and spectroscopic techniques that advance our understanding and guide the development of new transformations.