TANDEM ENYNE ALLENE-RADICAL CYCLIZATION VIA [3,3]-SIGMATROPIC REARRANGEMENTS

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 degrees C or by treatment with silver salts followed by heating at 75 degrees C.