The Cp2TiCl-mediated opening of epoxides in α,β-unsaturated ester-appended substrates
leads to a cascading 5-exo-trig radical cyclization followed by lactonization yielding
bicyclic lactone rings. Leveraging this strategic approach has become crucial in the
construction of the core structure of many terpenoid natural products. In our present
study, this methodology is further extended to the maleate/fumerate diester appended
substrates to give selectively only the 5-exo ring closure products with [5,5] bicyclic
lactone framework. This arranged the basis of a facile approach to attempt the synthesis
of lingzhilactone B, an important Ganoderma meroterpenoid with two all-carbon quaternary
chiral centers in the ring junction, from easily available starting material. The
modular strategy developed here can pave the synthetic pathways for many other natural
products of this genre.
