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  • Title: Efforts directed toward the synthesis of colchicine: application of palladium-catalyzed siloxane cross-coupling methodology.
    Author: Seganish WM, Handy CJ, DeShong P.
    Journal: J Org Chem; 2005 Oct 28; 70(22):8948-55. PubMed ID: 16238332.
    Abstract:
    [reaction: see text] Colchicine is an important and synthetically challenging natural product. The key synthetic step in this approach to the synthesis of colchicine involved a palladium-catalyzed cross-coupling reaction between 5-bromotropolone (4) and an aryl siloxane to form the aryl-tropolone bond. The coupling of a variety of highly functionalized aryl siloxane derivatives was investigated and optimized coupling conditions were developed. It was discovered that a palladium catalyst with a high degree of phosphine ligand coordination (5 equiv of phosphine/mol Pd) was necessary to efficiently couple aryl siloxanes with 5-bromotropolone (4). In addition, the coupling approach has provided a direct comparison between siloxane and boronic acid coupling technologies that demonstrated that aryl siloxanes and boronic acids produce similar yields of highly functionalized biaryl products.
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