New cycloaddition/fragmentation strategies for preparing 5-7-5 and 5-7-6 fused tricyclic ring systems

Tethering additional functionality to cyclobutadienyl iron tricarbonyl complexes provides new opportunities for the rapid construction of medium-ring-containing polycyclic compounds. Specifically, an intramolecular cycloaddition between cyclobutadiene and a tethered olefin, followed by an intramolecular cyclopropanation of the resulting cyclobutene-containing adduct generates highly strained pentacyclic intermediates. These compounds can then be relaxed thermally to generate 5-7-5 and 5-7-6 fused tricyclic ring systems that are shared with numerous natural products.