Facile Generation of Fused Seven-Membered Polycyclic Systems via Ring Expansion and Application to the Total Synthesis of Sesquiterpenoids

Seven-Membered polycyclic architectures, widely present in natural products and small molecular drugs, are challenging synthetic targets. So far, methods for synthesizing fused medium-sized bicyclo[m.n.0] ring systems, including the benzocycloheptane systems, are still surprisingly underdeveloped due to the lack of a general protocol to access these architectures. Herein we describe a base-induced ring expansion as a general strategy, which enables rapid and efficient construction of a wide range of fused seven-membered ring systems. The application of this method was demonstrated by the efficient total syntheses of two sesquiterpenoids plecarpenene and plecarpenone, both bearing a fused bicyclo[5.3.0]decane skeleton.