Recent advances in the stereoselective synthesis of L ‐phosphinothricin

L‐Phosphinothricin, the parent α‐amino acid of the herbicide glufosinate‐ammonium, has been obtained in high enantiomeric purity by three different methods. The stereoselective alkylation of a D‐valine‐derived bis‐lactim ether, followed by the hydrolysis of the heterocyclic intermediate, represents an attractive approach for gram‐scale quantities in the laboratory. Another very efficient access to L‐phosphinothricin consists of the asymmetric hydrogenation of a prochiral α‐acylamido acrylate with a chiral bis‐phosphine‐rhodium catalyst, while the reaction of chiral pre‐built C‐4‐fragments, like L‐vinylglycine or L‐2‐amino‐4‐halobutyric acid, which can be obtained from the inexpensive starting materials L‐aspartic acid and L‐glutamic acid, with (methyl)phosphinic acid derivatives represents a third route which allows the production of nearly enantiomerically pure L‐phosphinothricin.