Synthetic Studies of Carbapenem and Penem Antibiotics. V. Efficient Synthesis of the 1β-Methylcarbapenem Skeleton

An efficient synthesis of 1β-methylcarbapenem from the 1-(2-oxoazetidinyl)acetate 8 was developed by application of the Dieckmann reaction. Dieckmann-type cyclization of 8 and conversion to the enolphosphate 10 were achieved without epimerization to the 1α-methyl isomer in a one-pot procedure. Treatment with the mercaptan 22 after the phosphorylation resulted in a practical one-pot preparation of the 1β-methylcarbapenem derivative 23 from 8.