Synthetic studies of 1-beta-methylcarbapenem antibiotics

The diastereoselective synthesis of the 1-beta-methylcarbapenems, (1R,5R,6S)-6-((R)-1-hydroxyethyl)-2-((S)-1-acetimidoylpyrrolidin-3 - ylthio)-1- methyl-1-carbapen-2-em-3-carboxylic acid and sodium (1R,5R,6S)-6-((R)-1-hydroxyethyl)-2-(5-chloro-2-oxobenzoxazolin-3- y l)-1- methyl-1-carbapen-2-em-3-carboxylate has been achieved. The key step was an aldol reaction between the achiral boron enolate which was generated from dibutylboron triflate and 3-propionyl-2-oxobenzoxazoline, and (3R,4R)-4-acetoxy-3-((R)-1-hydroxyethyl)azetizin-2-one.