146.Synthesis of 4-Desmethyl-Rippertenol and 7-Epi-Rippertenol via Photoinduced Cyclization of Dienones

Zi-Chun Zhang†, Dan-Dan Zhao†, Zhong-Chao Zhang, Xin-Yu Tan, Jian-Xian Gong*, Jun-Kai Fu* & Zhen Yang*

Chinese Chemical Society, 2020, 2(5), 2074–2083

The synthesis of cycloheptanoid-based fused polycyclic frameworks is a challenge for organic chemists due to unfavorable entropic factors and ring strains. Herein, a concise synthesis of 4-desmethyl-rippertenol and 7-epi-rippertenol bearing a unique, [6,6,5,7]-fused tetracyclic framework is reported. The route features a novel photoinduced intramolecular cyclization of α-cyclopropyl dienone followed by an unexpected thermal 1,5-hydrogen migration, which provides efficient access to the fused seven-membered ring system in a stereochemically well-defined manner. Further density functional theory (DFT) calculations disclose that the stereoselectivity of this photoinduced process is mainly attributed to transition state conformation and steric effects.