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Gold- or Silver-Catalyzed Syntheses of Pyrones and Pyridine Derivatives: Mechanistic and Synthetic Aspects

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Preindl,  Johannes
Research Department Fürstner, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Jouvin,  Kévin
Research Department Fürstner, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Laurich,  Daniel
Research Department Fürstner, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Seidel,  Günter
Research Department Fürstner, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Fürstner,  Alois
Research Department Fürstner, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Citation

Preindl, J., Jouvin, K., Laurich, D., Seidel, G., & Fürstner, A. (2016). Gold- or Silver-Catalyzed Syntheses of Pyrones and Pyridine Derivatives: Mechanistic and Synthetic Aspects. Chemistry – A European Journal, 22(1), 237-247. doi:10.1002/chem.201503403.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0029-643C-8
Abstract
3-Oxo-5-alkynoic acid esters, on treatment with a carbophilic catalyst, undergo 6-endo-dig cyclization reactions to furnish either 2-pyrones or 4-pyrones in high yields. The regiochemical course can be dialed in by the proper choice of the alcohol part of the ester and the π-acid. This transformation is compatible with a variety of acid-sensitive groups as witnessed by a number of exigent applications to the total synthesis of natural products, including pseudopyronine A, hispidine, phellinin A, the radininol family, neurymenolide, violapyrone, wailupemycin and an unnamed brominated 4-pyrone of marine origin. Although the reaction proceeds well in neutral medium, the rate is largely increased when HOAc is used as solvent or co-solvent, which is thought to favor the protodeauration of the reactive alkenyl-gold intermediates as the likely rate-determining step of the catalytic cycle. Such intermediates are prone to undergo diauration as an off-cycle event that sequesters the catalyst; this notion is consistent with literature data and supported by the isolation of the gem-diaurated complexes 12 and 15. Furthermore, silver catalysis allowed access to be gained to 2-alkoxypyridine and 2-alkoxyisoquinoline derivatives starting from readily available imidate precursors.