Spirophosphine-Catalyzed\nEnantioselective [3 + 2]\nCycloaddition of Allenoates and Unsaturated α‑Ketimine\nEsters

A novel chiral spiro-monophosphine, OUC-Phos, was synthesized\nand\nutilized for the first time in the asymmetric Lu’s [3 + 2]\ncycloaddition reaction of β,γ-unsaturated α-ketimine\nester with allenoate. OUC-Phos, featuring a 3,3′-diphenyl-modified\nspirobiindane skeleton, demonstrated exceptional catalytic efficiency\nin the [3 + 2] cycloaddition to achieve high yields, enantioselectivities,\nand diastereoselectivities for the targeted products. The broad substrate\nscope encompassing diverse functional groups demonstrated the versatility\nof this methodology. Furthermore, the reaction was successfully scaled\nup, and the products were easily converted into their corresponding\nfunctionalized derivatives.