We report the first biomimetic syntheses of (-)-gochnatiolides A-C and (-)-ainsliadimer B based on our proposed biogenetic pathway. Our synthesis features one-pot cascade transformations including Saegusa oxidation, intermolecular Diels-Alder cycloaddition, and radical-mediated allylic oxidation, which allow for the rapid generation of (-)-gochnatiolides A-C in a collective manner. We also disclose an unprecedented "copper effect" on the stereochemical outcome of the radical-mediated allylic oxidation. Our synthetic endeavors led to the structural reassignment of (-)-gochnatiolide B. Ultimately, a biomimetic transformation from gochnatiolide B to ainsliadimer B was achieved through a remarkable direct enone hydration.