Cycloaromatization of a non-conjugated polyenyne system: Synthesis of 5H-benzo[d]fluoreno[3,2-b]pyrans via diradicals generated from 1-[2-{4-(2-alkoxymethylphenyl)butan-1,3-diynyl}]phenylpentan-2,4-diyn-1-ols and trapping evidence for the 1,2-didehydrobenzene diradical
Non-conjugated tetraynes 1 undergo thermal intramolecular cyclization to non-benzenoid diradicals (23) followed by radical cycloaromatization at 25 °C to provide 7-dehydro-5H-benzo[d]fluoreno[3,2-b]pyran monoradical (24) and alkyl radicals (25). Hydrogen abstraction of 24 gives 5H-benzo[d]fluoreno[3,2-b]pyrans (3) which are converted to 4 by reaction with 25. On the other hand, 2 gives 5H-fluorenol (5), indicating
非共轭四炔1经历热分子内环化反应生成非苯并双自由基(23),然后在25°C进行自由基环芳构化,以提供7-脱氢-5 H-苯并[ d ]氟[3,2- b ]吡喃单自由基(24)和烷基(25)。24的氢原子提取得到5 H-苯并[ d ]芴[3,2- b ]吡喃(3),可通过与25反应转化为4。另一方面,2得到5 H-芴醇(5),表明形成了1,2-二氢苯双自由基中间体(28和29)。这些自由基通过与芳族二烯,蒽反应而被捕获为相应的Diels-Alder型产物。
Synthesis of Indeno[1,2-b]phenanthrene-Type Heterocycles by Cycloaromatization of Acyclic Non-conjugated Benzotetraynes