Preparation method for glufosinate

A method for preparing glufosinate of formula (I);

• or a salt, an enantiomer or a mixture of enantiomers thereof, the method comprising steps of:
• a) reacting a compound of formula (II):
• or a salt, an enantiomer or a mixture of enantiomers thereof,
• with one or more compounds of formula (III) or a mixture to form an intermediate, the mixture comprising:
• one or more compounds of the formula (IV) and one or more compounds of formula (V);
• one or more compounds of the formula (IV) and one or more compounds of the formula (III);
• one or more compounds of formula (V) and one or more compounds of the formula (III);
• or
• one or more compounds of the formula (III), one or more compounds of the formula (IV) and one or more compounds of the formula (V)
• b) reacting the intermediate, isolated or not isolated, in the presence of water and an acid or a base to obtain the glufosinate of the formula (I) or the salt, the enantiomer or the mixture of enantiomers thereof,
• wherein when PG is an amino protecting group, the method further comprises a step of removing the amino protecting group, and
• wherein:
• Hal1 and Hal2 are each independently halogen;
• PG is hydrogen or an amino protecting group;
• R1, R2, R3 and R4 are each independently alkyl, phenyl or substituted phenyl, and when the mixture comprises one or more compounds of the formula (IV) and one or more compounds of the formula (III), or when the mixture comprises one or more compounds of the formula (III), one or more compounds of the formula (IV) and one or more compounds of the formula (V), R2 is either R3 or R4;
• and
• the chiral carbon atom is labeled with *.