Novel synthetic strategy toward abietane and podocarpane-type diterpenes from(-)-sclareol:synthesis of the antitumor (+)-7-deoxynimbidiol

摘要

A new route to abietane and podocarpane-type terpenoids from labdane diterpenes is reported.The key step is the transformation of beta-ketoester 9 into the corresponding O-acetylsalicylate ester 18,via a manganese(III)-based oxidative free-radical cycli-zation carried out in Ac2O.Utilizing this,the synthesis of the antitumor(+)-7-deoxynimbidiol(5)from(-)-sclareol(11)has been achieved.(+)-Nimbidiol(6)and the natural terpenoid 20 have also been synthesized.