Stereoselective Synthesis of 3-Hydroxyproline Benzyl Esters from N-Protected β-Aminoaldehydes and Benzyl Diazoacetate

The synthesis of a series of 3-hydroxyproline benzyl esters from alpha-alkyl and alpha-alkoxy N-protected aminoaldehydes with benzyl diazoacetate is described. Aldehydes with alpha-alkyl substituents afforded prolines as a single diastereomer with a trans-cis relative configuration in 14-77%. An alpha-tert-butyldimethylsilyloxy aminoaldehyde afforded a proline as a single diastereomer with a trans-trans relative configuration in 37% yield.