Abstract
The 4-chloroazetidinone 10, a very reactive chiral intermediate for 1-.beta.-methylcarbapenems (1b), was easily prepared and isolated as a solid crystalline compound from the corresponding sulfide 5. Another chiral intermediate (16d) bearing the 1-.beta.-methyl moiety was prepared by stereoselective aldol type condensation of either azetidinone 4 or 10 with metal enolates 14. The .beta./.alpha. ratios were 9:1, 3:1, and 2:1 respectively.