An Efficient Synthesis of Phenanthroindolizidine Core via Hetero Diels-Alder Reaction of In Situ Generated α-Allenylchalcogenoketenes With Cyclic Imines

Synthesis of phenanthroindolizidine core was efficiently achieved through a pathway involving hetero Diels-Alder reaction of α-allenylchalcogenoketenes, generated in situ by thermal [3,3] sigmatropic rearrangement of alkynyl propargyl sulfides or selenides, with cyclic imines and the subsequent iodine-assisted photochemical cyclization.