Oxazoline Chemistry. Part 11: Syntheses of natural and synthetic isoflavones, stilbenes and related species via C-C bond formation promoted by a Pd-oxazoline complex

The complex trans-[PdCl2(2-ethyl-2-oxazoline-kappa N-1)(2)] (1) is shown to be an active and oxidatively robust catalyst for C-C bond forming reactions (Heck, Sonogashira, Ullmann, Miyaura-Suzuki, etc.). These reactions can be carried out in air without rigorous solvent/ substrate purification and in the absence of additional free ligand. The general methodology described above has been applied to the high yield and regio-selective formation, via Miyaura-Suzuki coupling, of natural and synthetic isoflavones (i.e., isoflavone, 2'-methylisoflavone [7b], 3'-methylisoflavone [7c] and 3',4'-benzoisoflavone: [7d]). Compounds 7c and 7d are previously unknown. In addition, the synthesis of (E)-tris-O-methylresveratrol and (E)-3,5-dimethoxystilbene is also described; the former is a recognized anti-cancer agent while the latter is a biologically active extract from the bark of the conifer species Pinus armandii. Both of these latter products are produced as a result of a Heck coupling reaction promoted by 1. (c) 2006 Elsevier Ltd. All rights reserved.