Abstract An efficient diastereoselective multi-step synthesis of bicyclic 1β- methylcarbapenem antibiotic precursors has been developed, starting from the commercially available 4-acetoxyazetidin-2-one 4. Chiral ruthenium catalysts are used in the hydrogenation step to control the β-stereochemistry at the 1-position, and a π- allylpalladium ring-closure strategy is used to form the functionalized carbapenem ...