Transformation of Glutamic Acid into (S)-Benzyl 2-(dibenzylamino)- 6-(dimethoxyphosphoryl)-5-oxohexanoate for a Convenient Access to 5-Substituted Prolines.

L-Glutamic acid was transformed into δ-keto-phosphonate in two steps. This compound was employed in the stereocontrolled synthesis of cis-5-substituted prolines through a Woodward-Horner-Emmons (WHE) reaction with different aldehydes followed by hydrogenolysis/hydrogenation-mediated ring closure. We found also that a one-pot sequential hydroformylation - WHE reaction was possible with cis-5-substituted prolines. In addition to differently functionalised prolines, an indolizidine amino acid with a structure related to constrained peptidomimetics was obtained