Total Syntheses of the Tetracyclic Cyclopiane Diterpenes Conidiogenone, Conidiogenol, and ConidiogenoneB

摘要

Total syntheses of the biologically important and structurally unique tetracyclic diterpenes conidiogenone, conidiogenol, and conidiogenoneB of the cyclopiane class are reported. The absolute configuration of naturally occurring conidiogenoneB was also corrected. The key step of our strategy involved the highly efficient construction of both ringC and the quaternary carbon center shared by rings A and C through a one-step regioselective and diastereoselective cycloenlargement in the form of a semipinacol-type rearrangement. In particular, the desired regioselectivity was made possible by properly adjusting the migratory aptitude of the migrating carbon atom through the introduction of an electron-donating phenylthio group at this position.