Diastereoselective Synthesis of γ-Phthalimido-β-Hydroxy Esters and N-Protected 4-Amino-1,3-Diols Starting from Natural α-Amino Acids

An efficient diastereoselective synthes.is of γ-phthalimido-β-hydroxy esters and N-protected 4-amino-1,3- diols, starting from natural amino acids is described. The key synthetic strategies involve diastereoselective reduction of γ-phthalimido-β-keto esters with NaBH4 as hydride reducing. The diastereoselective reduction has been found to be highly selective if carried out in methanol at -78°C. Furthermore, the resulting diastereomeric mixture of the reduced products was successfully and cleanly separated by column chromatography.