Preparation method for glufosinate

A method for preparing a glufosinate compound of formula (I), a salt thereof, an enantiomer thereof, or a mixture of enantiomers thereof, which enantiomers may be present in any ratio,

• wherein the method comprises the following steps:
• a) reacting a compound of formula (II) or a salt thereof, an enantiomer thereof or a mixture of enantiomers thereof, which enantiomers may be present in any ratio,
• with one or more compounds of formula (III) or a mixture;
• wherein said mixture comprises one or more compounds of formula (IV) and one or more compounds of formula (V);
• or one or more compounds of formula (IV) and one or more compounds of formula (III);
• or one or more compounds of formula (V) and one or more compounds of formula (III);
• or one or more compounds of formula (III), one or more compounds of formula (IV), and one or more compounds of formula (V),
• wherein the reaction of a) results in a “reaction intermediate”;
• b) reacting the reaction intermediate which results from step a), wherein said reaction intermediate may or may not be in isolated form, with an acid or a base to obtain a glufosinate compound of formula (I) or a salt thereof, an enantiomer thereof, or a mixture of enantiomers thereof, which enantiomers may be present in any ratio;
• wherein when PG is an amino protecting group, the method further optionally includes the removal of the amino protecting group;
• further wherein:
• LG is Hal1, —OTs or Hal1
• Hal1 and Hal2 are each independently halogen selected from fluorine, chlorine, bromine or iodine;
• PG is hydrogen or an amino protecting group selected from —C(═O)R, —C(═O)OR and —S(═O)2R;
• A is —NHR1, —NR1R1′, or —OR1;
• R, R1, R1′, R2, R3 and R4 are each independently selected from the group consisting of C1-C6 alkyl, C3-10 cycloalkyl, C6-10 aryl, C6-12 aralkyl, 5- to 14-membered heteroaryl and 3- to 10-membered heterocyclyl,
• with the further proviso that when the mixture comprises a mixture of one or more compounds of formula (IV) and one or more compounds of formula (III);
• or a mixture of one or more compounds of formula (III), one or more compounds of formula (IV) and one or more compounds of formula (V);
• then
• R2 is either R3 or R4;
• and
• the chiral carbon atom is labeled with *;
• and
• with the further proviso that at least one of the following conditions is met:
• 1) the compound of formula (II) is not
• 2) the compound of formula (III) is not
• 3) the compound of formula (IV) is not
• 4) the compound of formula (V) is not