Bisphosphine-Triggered One-Pot Sequential [3 + 2]/[3 + 2] Annulation of Allenoates with Cyclic Ketimines

An efficient bisphosphine-triggered one-pot sequential [3 + 2]/[3 + 2] annulation of allenoates with cyclic ketimines was developed, in which the product of the first [3 + 2] annulation is the electron-deficient substrate for the second [3 + 2] annulation reaction. The reaction is exceptionally regioselective and diastereoselective. This novel and highly convergent strategy may open up a new viewpoint in utilizing allenoates to prepare <i>N</i>-fused polycyclic compounds