Based on the structural similarities of the recently isolated eremophilane-type sesquiterpenoids microsphaeropsisin Ba nd Ca nd the iso-eremophilane periconianone C, ar evised biogenetic hypothesis for C8-C11-connected isoeremophilanes is presented and corroborated by strong experimental evidence.The first enantioselective total syntheses of microsphaeropsisin Ba nd Cw ere achieved starting from ak nowni ntermediate,w hose synthesis was elaborated previously in the total synthesis of periconianone A, and in atotal of 15 steps starting from g-hydroxy carvone.M ild reaction conditions for the subsequent a-ketol rearrangement not only resulted in the herein proposed conversion of microsphaeropsisin Bi nto periconianone C, but also in the conversion of microsphaeropsisin Ci nto 4-epi-periconianone C.

Based on the structural similarities of the recently isolated eremophilane-type sesquiterpenoids microsphaeropsisin Ba nd Ca nd the iso-eremophilane periconianone C, ar evised biogenetic hypothesis for C8-C11-connected isoeremophilanes is presented and corroborated by strong experimental evidence.The first enantioselective total syntheses of microsphaeropsisin Ba nd Cw ere achieved starting from ak nowni ntermediate,w hose synthesis was elaborated previously in the total synthesis of periconianone A, and in atotal of 15 steps starting from g-hydroxy carvone.M ild reaction conditions for the subsequent a-ketol rearrangement not only resulted in the herein proposed conversion of microsphaeropsisin Bi nto periconianone C, but also in the conversion of microsphaeropsisin Ci nto 4-epi-periconianone C.