Phosphine-Catalyzed Intramolecular 7- <i>endo</i> - <i>trig</i> Annulations for Synthesis of Cycloheptadienes

Phosphine-catalyzed activation of allenoates provides efficient access to carbo- and heterocycles. However, the development of extended allenoates as synthons via this strategy remains underexplored. Herein, we report a phosphine-catalyzed remote nucleophilic addition employing α-allyl γ-benzyl allenoates as C7 synthons. This reaction proceeds through a distinctive δ to δ' addition followed by proton-promoted uncyclization, enabling efficient and highly chemoselective synthesis of cycloheptadienes from a wide range of substrates. This work establishes a versatile platform for C7 annulation, expanding the synthetic utility of phosphine catalysis beyond conventional cyclization modes.