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 (55–73 %), and with moderate to excellent regioselectivity.