Iron-Catalyzed Radical Allylic Substitution of Unprotected Allylic Alcohols.

Allylic substitution reactions are essential in organic synthesis, enabling the transformation of allylic reagents into diverse alkenes. Traditional methods, which typically operate through ionic pathways, often require substrate preactivation to address high C─O bond dissociation energies, leading to challenges in regioselectivity and limited substrate compatibility. Here, we introduce an iron-catalyzed radical pathway for allylic substitution that directly activates unprotected allylic alcohols, leveraging the redox and oxophilic properties of low-valent iron to promote selective C─O bond cleavage and allylic transposition. This radical approach achieves high regio- and stereoselectivity, providing access to a broad array of di-, tri-, and tetra-substituted alkenes with moderate to excellent yields and exceptional E/Z selectivity. Mechanistic studies confirm that the iron catalyst generates radical intermediates and mediates efficient dehydroxylation, enabling this direct transformation without protective groups or Lewis acid activators. The method's versatility is demonstrated through a broad substrate scope, including complex natural derivatives and functionalized alkyl halides, along with successful gram-scale synthesis and downstream derivatization. This iron-catalyzed radical pathway offers a sustainable and efficient alternative to conventional ionic methods, expanding the scope of allylic substitutions and advancing radical-based methodologies in synthetic chemistry.