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  • Title: Total synthesis of an exceptional brominated 4-pyrone derivative of algal origin: an exercise in gold catalysis and alkyne metathesis.
    Author: Hoffmeister L, Fukuda T, Pototschnig G, Fürstner A.
    Journal: Chemistry; 2015 Mar 16; 21(12):4529-33. PubMed ID: 25712698.
    Abstract:
    A concise approach to the algal metabolite 1 is described, which also determines the previously unknown stereostructure of this natural product. Compound 1 is distinguished by a rare brominated 4-pyrone nucleus linked as a ketene-acetal to a polyunsaturated macrocyclic scaffold comprising an extra homoallylic bromide entity. The synthesis of 1 is based on the elaboration and selective functionalization of the linear precursor 23 endowed with no less than six different sites of unsaturation including the highly enolized oxo-alkanoate function. Key to success was the formation of the 2-alkoxy-4-pyrone ring by a novel gold-catalyzed transformation which engages only the acetylenic β-ketoester substructure of 23 but leaves all other π-bonds untouched. The synthesis was completed by a ring-closing alkyne metathesis to forge the signature cycloalkyne motif of 1 followed by selective bromination of the ketene-acetal site in the resulting product 27 without touching the skipped diene-yne substructure resident within the macrocyclic tether.
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