Thermal and Electron‐Transfer Induced Reactions of Enediynes and Enyne‐Allenes, 9. Electron‐Transfer versus Acid Catalysis in Enediyne Cyclizations

Four novel aryl‐substituted enediynes 3 have been synthesized. While their cyclization to the Bergman products 4 could be accomplished at temperatures of 240–320°C, α‐functionalization rather than cyclization was observed during anodic oxidation and in the presence of one‐electron oxidants. In contrast, enediyne 1a was cyclized in the presence of two one‐electron oxidants to the indenone 2a as indicated in the literature; mechanistic investigations clearly indicate the occurrence of an acid‐catalyzed mechanism.