Total Synthesis of d,l-Isospongiadiol: An Intramolecular Radical Cascade Approach to Furanoditerpenes.
A stereoselective oxidative free-radical cyclization of beta-keto ester polyenes 7 and 19 has been accomplished as a one-step entry to the tricarbocyclic synthons 8and 21 which contain five and six stereogenic centers, respectively. These key synthons possessing an axial carboethoxy group at C-4 were ultimately converted to the spongian skeleton (8--> 14 and 21 --> 25 -->14). The synthesis of d,l-isospongiadiol (3) from the common intermediate 14 was realized after introduction of the 2alpha-hydroxy group in the spongian A-ring via epoxidation of silyl enol ether 28 and subsequent desilylation.
Zoretic
Phillip A.
PA
Duke NMR Spectroscopy Center, Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710.
Wang
Ming
M
Zhang
Yongzheng
Y
Shen
Zhongqi
Z
Ribeiro
Anthony A.
AA