Tandem Eneyne Allene-Radical Cyclization via [3,3] Sigmatropic Rearrangements

Abstract

Enediynes (1), (7), (12), and (16) undergo a tandem [3,3] sigmatropic shift-enyne allene cyclization. Enediynes (7) and (16) are especially interesting because after undergoing a [3,3] sigmatropic shift and enyne allene cyclization, the resultant biradical undergoes a 5-exo radical cyclization. These reactions can be effected by either heating at 150 o C or by treatment with silver salts followed by heating at 75 o C