Chemical process for the synthesis of herbicidal pyrazolidinedione compounds

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

• wherein
• each R1 and R2 are independently C1-C4alkyl;
• R3 is selected from the group consisting of hydrogen and C1-C4alkyl;
• said process comprising reacting a compound of formula (II)
• wherein
• X is selected from the group consisting of Br, Cl, CF3SO3−, CH3C6H4SO3− and CH3SO3−, and R1,
• R2 and R3 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
• R4 is selected from the group consisting of C1-C6alkyl, C5-C6cycloalkyl, 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 R5 substituents, which may be the same or different;
• R5 is selected from the group consisting of halogen, C1-C4alkyl, C1-C4alkoxy, N—C1-C4alkylamino, N,N-diC1-C4alkylamino and phenyl, wherein said phenyl is optionally substituted by 1, 2, 3 or 4 R6 substituents, which may be the same or different;
• R6 is selected from the group consisting of C-C4alkoxy, N—Cl-C4alkylamino and N,N-diC1-C4alkylamino;
• and a base.