Palladium(0)-catalyzed allylation of uracils and 2-thiouracils drastic effect on an aqueous reaction medium on the regioselectivity

Article abstract of DOI:10.1016/0040-4039(94)88232-0

Palladium(0)-catalyzed allylation of uracils in DMSO takes place at N-1 and at N-3. In sharp contrast, regiospecific allylation at N-1 is achieved in an organic-aqueous medium in the presence of palladium(II) acetate and the water-soluble sulfonated triphenylphosphine P(C₆H₄-m-SO₃Na)₃ (tppts). Similar reactions with 2-thiouracils are also drastically dependent on the solvent, taking place at N-1 and N-3 (in dioxane) or at sulfur (organic-aqueous medium). Probably reactions in the organic aqueous medium are kinetically controlled whereas allylation in DMSO or refluxing dioxane are thermodynamically controlled.