Total Synthesis of ent-Lepadin F and G by a Tandem Ene−Yne−Ene Ring Closing Metathesis

The first total synthesis of the decahydroquinoline-alkaloids lepadin F and G is described. As key steps, the decahydroquinoline skeleton has been synthesized by utilizing a tandem ene−yne−ene ring closing metathesis of an acyclic precursor followed by a stereoselective hydrogenation of the resulting diene moiety. The selectivity of these two steps was achieved by a well-directed hydroxyl protection strategy. The synthesized compounds were found to be enantiomers of natural lepadin F and G, consequently the absolute configuration of the natural compounds could be assigned.