Variation of xanthene-based bidentate ligands in the palladium-catalyzed arylation of ureas

A series of xanthene-based bidentate ligands containing various substituents on diphenylphosphino groups were synthesized and tested in the palladium-catalyzed arylation reaction of urea with unactivated aryl bromides. It was found that both steric and electronic properties of the ligands have a pronounced effect on the yields and ratios of the products. Arylation of urea and phenylurea with unactivated aryl bromides in the presence of Pd₂dba₃·CHCl₃/3,5-(CF₃)₂Xantphos and Cs₂CO₃ as base in dioxane at 100°C gave the corresponding N,N′-diarylureas in 62-98% yields.