A novel and practical total synthesis of a tricyclic β-lactam antibiotic, GV104326 (4-methoxytrinem or Sanfetrinem) has been achieved in nine steps and about 33% overall yield from a commercially available acetoxyazetidinone chiron. A key step in the highly diastereoselective synthesis is a protonation of a zinc enolate complex which circumvents the use of enantiomerically pure (S)-2-methoxycyclohexanone. A mechanistic rationale is presented and experimentally verified.