Intramolecular [3 + 2] annulation of allenylsilane-enes: Direct synthesis of highly strained trans-fused 5/5 ring systems

The first asymmetric total synthesis of β-funebrene, which contains a highly strained trans-fused 5/5 ring system, has been achieved. The synthetically challenging and multi-functionalized trans-fused 5/5 ring systems were diastereoselectively and efficiently constructed by the first intramolecular [3 + 2] annulation reaction of allenylsilane-enes. This simple, direct transformation shows broad substrate scope and is stereospecific. Thus, this work represents the first stereoselective approach for the direct synthesis of trans-fused 5/5 ring systems from acyclic precursors.