Synthesis of cassane-type diterpenes from abietane compounds: the first synthesis of taepeenin F

Abstract

The first synthesis of the aromatic cassane-type diterpene taepeenin F from abietic acid is reported. The key steps of the synthetic sequence are the ipso-substitution of the isopropyl group of a dehydroabietane derivative by a formyl group, after treatment with Cl₂CHOMe and AlCl₃, and the oxidative cleavage of a dihydronaphthalene intermediate. The deisopropylation reaction of dehydroabietane derivatives is revised and a complementary study on this subject is included. A mechanism for this reaction is postulated.