アンセリジオーゲン-Anの合成研究

抄録

SmI₂-induced cascade reaction involving reductive cyclization, Dieckmann condensation and lactonization has been developed in our laboratory, and applied to the total synthesis of (+-)-gibberellin A₁. Herein, we report the further application of the reaction to the synthesis of antheridiogen-An, isolated from Anemia phyllitidis in 1971 by Nakanishi and coworkers, having unique tetracycic ring system with gamma-lactone. Our synthetic features for the challenging synthetic target were shown as follows. The CD ring was formed by SmI₂-induced fragmentation reaction of the cyclopropane ring in the tricyclo[3.2.1.0^2,7]octane derivative, prepared by Michael-Michael-alkylation reaction. Formation of functionalized antheridane skeleton as a key step was achieved by application of the SmI₂-induced reductive cyclization-Dieckmann condensation-lactonization of the keto diester as a intermediate.