Chemical process for the synthesis of herbicidal pyrazolidinedione compounds

1. A process for preparation of a compound of formula (I)

wherein

each R 1 and R 2 are independently C 1 -C 4 alkyl;

R 3 is selected from the group consisting of hydrogen and C 1 -C 4 alkyl;

said process comprising reacting a compound of formula (II)

wherein

X is selected from the group consisting of Br, Cl, CF 3 SO 3 —, CH 3 C 6 H 4 SO 3 — and CH 3 SO 3 —, and R 1 ,

R 2 and R 3 are as defined herein, with a compound of formula (III)

the reaction being carried out

in the presence of a π-allylpalladium complex;

and a phosphine ligand of the formula (IV)

or a suitable salt thereof,

wherein

R 4 is selected from the group consisting of C 1 -C 6 alkyl, C 5 -C 6 cycloalkyl, phenyl and heteroaryl,

wherein the heteroaryl is a 5- or 6-membered aromatic ring which comprises 1 or 2 heteroatoms independently selected from N and O,

and wherein the phenyl or heteroaryl are optionally substituted by 1, 2, 3, 4 or 5 R 5 substituents, which may be the same or different;

R 5 is selected from the group consisting of halogen, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, N—C 1 -C 4 alkylamino, N,N-diC 1 -C 4 alkylamino and phenyl, wherein said phenyl is optionally substituted by 1, 2, 3 or 4 R 6 substituents, which may be the same or different;

R 6 is selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 alkoxy, N—C 1 -C 4 alkylamino and N,N-diC 1 -C 4 alkylamino;

and a base.

2. A process according to claim 1 , wherein X is Br.

3. A process according to claim 1 , wherein each R 1 and R 2 are ethyl.

4. A process according to claim 1 wherein R 3 is methyl.

5. A process according to claim 1 , wherein the π-allylpalladium complex is selected from the group consisting of allylpalladium chloride, allylpalladium trifluoroacetate, (2-Butenyl) chloropalladium, palladium (π-cinnamyl) chloride and (2-methylallyl)palladium chloride.

6. A process according to claim 1 , wherein the π-allylpalladium complex is allylpalladium chloride or (2-Butenyl) chloropalladium.

7. A process according to claim 1 , wherein the π-allylpalladium complex is present in the amount of from 1 to 10 mol % based on the compound of formula (II).

8. A process according claim 1 wherein the molar ratio of π-allylpalladium complex to phosphine ligand or phosphine ligand salt is 1:4.

9. A process according to claim 1 , wherein the π-allylpalladium complex is provided with a phosphine ligand as defined herein in a pre-formed complex.

10. A process according to claim 1 , wherein the phosphine ligand of formula (IV) is 4-di-tert-butylphosphanyl-N,N-dimethyl-aniline.

11. A process according to claim 1 , wherein the organic solvent is 1,4-dioxane or toluene.

12. A process according to claim 1 , wherein the base is K 3 PO 4 .

13. A process according to claim 1 , wherein the reaction of a compound of formula (II) with a compound of formula (III) is at a temperature of from 80° C. to 110° C.

14. A compound of formula (III):

15. A process according to claim 1 , wherein a compound of formula (I) is further converted to pinoxaden.