Upon photolysis, the mixture of oxaziridines (shown separately here) undergoes a stereoselective ring expansion to yield a diastereomeric mixture of lactams, which are separated by column chromatography.  It is hypothesized that the bond antiperiplanar to the lone pair of electrons on the nitrogen migrates during the rearrangement.  A Birch reaction is performed on each lactam to remove the phenylethyl moieties to afford enantiomeric lactams.  The 3- and 5-benzyl-Aca linkers are obtained after hydrolysis of each lactam and formation of the corresponding methyl ester.   Back to Index            Synthesis of the 4-Benzyl-Aca Linker Stereochemistry of Lactam Formation