The isomerization of diterpene epoxides on active neutral alumina has established the existence of new rearrangements of the diterpene skeleton. Methyl 8,14β-epoxysandarcopimarate leads to bicyclic diterpene compounds by a Grob fragmentation, to derivatives of cleistanthane by a 1,2 migration of the vinyl substituent, as well as to one cycloditerpene compound. The 7,8 (or 8,9) derivatives of methyl isopimarate lead essentially to hydroxyolefins formed by a bifunctional acid–base mechanism at the alumina surface. [Journal translation]