Synthesis of optically active 1-aza-4-oxabicyclo[4.1.0]-heptan-5-ones

The reaction of the methyl ester of 1,2-dibromopropionic acid with chiral Β- aminoalcohols under the conditions of the Gabriel-Cromwell reaction gave epimers of methyl 1-(Β-hydroxyalkyl)aziridine-2-carboxylates, which were separated by liquid chromatography. NMR spectroscopy and CD were used to determine the absolute configuration of these products. The relative rate of conversion of epimeric esters of trans-1-(Β-hydroxyalkyl)aziridine-2-carboxylic acids to 1-aza-4- oxabicyclo-[4.1.0]heptan-5-ones is a function of the intramolecular contacts of the reacting OH and CO2Me groups in the lactonization of the cis isomers. The most favorable conformation of the six-membered ring in 1-aza-4-oxabicyclo[4,1,0]heptan-5-ones in solution is a distorted boat.