Synthesis of phenol abietane diterpenes based on the oxidative radical cyclization utilizing the Mn(OAc)3/Ac2O system

A new route to phenol abietane diterpenes from transcommunic acid is reported. The key step is the transformation of a eta-ketoester into the corresponding O-acetylsalicilate, via a manganese(III)-based oxidative free-radical cyclization carried out in Ac2O. Utilizing this, the first synthesis of (-)-sugikurojin A has been achieved. The immunosuppressor 19-hydroxyferruginol has also been synthesized.