Highly Ligand Controlled Regioselective Pd Catalyzed Aminocarbonylation of Styrenes with Aminophenols.
Achieving chemo and regioselectivity simultaneously is challenging in organic synthesis. Transition metal catalyzed reactions are effective in addressing this problem by the diverse ligand effect on the catalyst center. Ligand controlled regioselective Pd catalyzed carbonylation of styrenes with aminophenols was realized, chemoselectively affording amides. Using a combination of boronic acid and 5 chlorosalicylic acid as the additives, linear amides were obtained in high yields and selectivity using tris(4 methoxyphenyl)phosphine (L3) in acetonitrile, while branched amides were obtained in high yields and selectivity in butanone by changing the ligand to 1,3,5,7 tetramethyl 2,4,8 trioxa 6 phenyl 6 phosphaadamantane (L5) Further studies show that the nature of the ligand is key to the regioselectivity. Cone angle and Tolman electronic parameter (TEP) have been correlated to the reactivity and regioselectivity. Studies on the acid additives show that different acids act as the proton source and the corresponding counterion can help enhance the reactivity and selectivity.
Journal of the American Chemical Society