Epimerization and stapling in one pot: A facile synthesis of an oxazinidinyl analogue of the antibiotic platensimycin is presented. Key steps of this work are a novel dynamic ring-closing metathesis (RCM) that involves a base-catalyzed epimerization followed by a tandem Ru-catalyzed metathesis, and a nucleophilic addition to a ketone followed by a subsequent intramolecular epoxide ring-opening reaction to construct the core structure of the target molecule (see scheme).