Synthesis of Chiral Spirocyclopentenyl-β-lactams through Phosphane-Catalyzed [3+2] Annulation of Allenoates with 6-Alkylidenepenicillanates

The first examples of phosphane-catalyzed [3+2] annulation of allenoates to 6-alkylidenepenicillanates leading to chiral spirocyclopentenyl--lactams are reported. The synthesis of this new type of -lactams involved the generation of either two or three consecutive stereogenic centers, including a quaternary chiral center. Although the reported methodology is highly diastereoselective, the regioselectivity is dependent on the nature of the methylenepenicillanate derivative and on the nature of the allenoate gamma-substituent.