Phosphane-Catalyzed [4+2] Annulation of Allenoates with Ketimines: Synthesis of Sultam-Fused Tetrahydropyridines

Cyclic ketimines were successfully used as electrophiles in phosphane-catalyzed [4+2] annulation reactions with ethyl 2-methyl-2,3-butadienoate to give the corresponding highly substituted tetrahydropyridine derivatives in moderate to good yields (5573?%), and with moderate to excellent regioselectivity.