Asymmetric Synthesis of (l′R,3R,4R)-4-acetoxy-3-(l′-((tert-butyldimethylsilyl)oxy)ethyl)-2-azetidinone and Other 3-(r-hydroxyethyl)-2-azetidinones from (£)-(+)-ethyl 3-hydroxybutanoate: Formal Total Synthesis of (+)-thienamycin

The synthesis of (1′,3R,4R)-4-acetoxy-3-(R-((tert-butyldimethylsilyl)oxy)ethyl)-2-azetidinone, an important precursor for the synthesis of carbapenems and penems, is detailed. The methodology utilized relies on the addition, cyclization reaction between the dianion of (S)-(+)-ethyl 3-hydroxybutanoate and N-arylaldimines. The syntheses of other useful optically active 3-(hydroxyethyl)-2-azetidinones are presented. A study of factors influencing the stereochemistry in the addition, cyclization reaction for the formation of 3-(l′-hydroxyethyl)-2-azetidinones is detailed.