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 t heir cyclization to the Bergman products 4 could be accomplished at te mperatures of 240-320 degrees C, alpha-functionalization rather than c yclization was observed during anodic oxidation and in the presence of one-electron oxidants. In contrast, enediyne 1a was cyclized in the p resence of two one-electron oxidants to the indenone 2a as indicated i n the literature; mechanistic investigations clearly indicate the occu rrence of an acid-catalyzed mechanism.