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Synthesis of the Tricyclic Ring Structure of Daphnanes via Intramolecular [4 + 3] Cycloaddition/SmI2‑Pinacol Coupling

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posted on 2015-06-05, 00:00 authored by Ahmed H. E. Hassan, Jae Kyun Lee, Ae Nim Pae, Sun-Joon Min, Yong Seo Cho
A synthetic approach toward the tricyclic 5,7,6-membered ring structure of daphnane-family natural products is described. An intramolecular [4 + 3] cycloaddition reaction of furan with an oxypentadienyl cation constructed the oxa-bridged bicyclic structure in a stereoselective fashion. Structural analysis revealed that the desired exo isomer was predominantly acquired through epimerization. Finally, formation of the five-membered ring was achieved through SmI2-mediated pinacol coupling.