To a solution of 1.23 g of 2-{4-[3-(2-chloropyridin-4-ylmethyl)-4,4-dimethyl-2,5-dioxo-imidazolidin-1-yl]-phenyl}-2-methylpropionic acid methyl ester obtained in stage d) below in 40 mL of dioxane are successively added, under argon, 0.4 g of 3-aminopyridine, 0.16 g of (9,9-dimethyl-9H-xanthene-3,6-diyl)bis(diphenylphosphine) (Xantphos), 0.065 g of palladium acetate and 3.65 g of caesium carbonate. The reaction mixture is refluxed for 4 hours and then filtered and concentrated under reduced pressure. The residue is purified by chromatography on a column of silica, eluting with a mixture of dichloromethane and methanol (98/02 by volume) to give 0.96 g of methyl 2-[4-(4,4-dimethyl-2,5-dioxo-3-{[2-(pyridin-3-ylamino)pyridin-4-yl]methyl}imidazolidin-1-yl)phenyl]-2-methylpropanoate, the characteristics of which are as follows:
