Stille coupling for the synthesis of isoflavones by a reusable palladium catalyst in water

Abstract

Isoflavones were synthesized from the reaction of 3-bromochromone derivatives and aryltributylstannanes via Stille coupling catalyzed by a water-soluble and reusable PdCl 2 (NH 3) 2 /2,2 0-cationic bipyridyl system in aqueous solution. For prototype 3-bromochromone, the coupling reaction was performed at 80 C for 24 hr with 2.5 mol% catalyst in water in the presence of tetrabutylammonium fluoride. After the reaction, the aqueous solution could be reused for several runs, indicating that its activity was only slightly decreased. For substituted 3-bromochromones, the addition of NaHCO 3 and a higher reaction temperature (120 C) were required to gain satisfactory outcomes. In addition, naturally occurring products, such as daidzein, could be obtained by this protocol via a one-pot reaction.