Enantioselective Synthesis of the Key Intermediate of a 1β-Methylcarbapenem Antibiotic by Way of Nitrone 1,3-Dipolar Cycloaddition.

Synthesis of the key intermediate of the 1β-methylcarbapenem antibiotic (1) was investigated by way of inter- and intramolecular nitrone 1,3-dipolar cycloaddition. A highly enantioselective construction of (3S,4R)-(–-)-3-[(1R)-1-(t-butyldimethylsiloxy)ethyl]-4-[(1R)-1-(hydroxymethyl)ethyl]azetidin-2-one (2) was achieved via intramolecular cycloaddition of the nitrone (6).