Enantioselective Synthesis of Chiral Exocyclic Allenes via Pd-Catalyzed Asymmetric [4 + 2] Cycloaddition

Exocyclic allenes represent an important class of allene-containing natural products, in which axial chirality is embedded within a rigid cyclic framework, making them attractive motifs for bioactive molecule discovery. Herein, we report the design and synthesis of novel allenyl carbonates that act as oxa-1,4-dipoles under palladium catalysis and participate in asymmetric [4 + 2] cycloadditions with electron-deficient alkenes. This strategy provides rapid access to structurally diverse and highly functionalized chiral exocyclic allene derivatives in moderate to excellent yields with high stereoselectivities, delivering products in up to 95% yield, >19:1 dr, and 99% ee. A scale-up reaction proceeds with comparable efficiency and stereocontrol, demonstrating the synthetic utility of this method. This work establishes a modular catalytic platform for the stereoselective synthesis of chiral exocyclic allenes.