Synthesis of the 5-7-6 Core of Guanacastepenes. Construction of C8 Quaternary Carbon via the Inversion of Stereochemistry

摘要

An efficient and unique route to the 5-7-6 core of guanacatepene A(1) is described. The installation of the desired stereochemistry at the C8 position was achieved via the desymmetrization of the cyclohexadienone by reductive ring closure of the seven-membered ring. That the closure of the seven-membered ring produced only the desired isomer is hypothesized to be a result of the more stable trans relationship between the C8 and C11 methyl groups.