Facile synthesis of the trans-fused azabicyclo[3.3.0]octane core of the palau'amines and the tricyclic core of the axinellamines from a common intermediate

A facile synthesis of the trans-fused azabicyclo[3.3.0]octane core of palau'amine and related pyrrole-imidazole alkaloids is described. Following gamma-lactam cleavage with concomitant epimerization at C12 of a previously reported tricycle, a facile intramolecular Mitsunobu reaction delivered the fully functionalized tricyclic core common to several members of the oroidin-derived alkaloids including palau'amine. An alternative cyclization of a related intermediate provides the tricyclic "aza-angular triquinane" core of the axinellamines.