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| http://dx.doi.org/10.1016/j.tet.2018.04.006 | DOI Listing |
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Intermolecular Oxidopyrylium (5 + 2) Cycloaddition/Reductive Ring-Opening Strategy for the Synthesis of α-Methoxytropones.
J Org Chem
December 2024
Department of Chemistry, Brooklyn College, The City University of New York, Brooklyn, New York 11210, United States.
α-Methoxytropone is a structural motif found in various natural products and other compounds of interest to the scientific community but remains a synthetic challenge. The present Note describes the synthesis of variously substituted α-methoxytropones and related compounds through an intermolecular 3-hydroxy-4-pyrone-based oxidopyrylium (5 + 2) cycloaddition followed by a samarium iodide-mediated reductive ring-opening. The strategy is highlighted in the synthesis of a novel AC-ring analogue of colchicine to compare it to existing methods.
View Article and Find Full Text PDFRoutes to Advanced Intermediates in the Synthesis of Tetracarbocyclic Sesquiterpenoids Daphnenoid A and Artatrovirenols A and B.
Org Lett
March 2024
Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, United Kingdom.
A short route from dihydrocarvone is described, which led to the tetracarbocyclic core common to artatrovirenol A and B and daphnenoid A. A variant of this route afforded guaia-4,6-dien-3-one (from ) and its epimer. From 2-(2-oxoethyl)furan, a 15-step sequence then delivered the complete carbon skeleton and all functionality necessary for daphnenoid A.
View Article and Find Full Text PDFNet Intermolecular Silyloxypyrone-Based (5+2) Cycloadditions Utilizing Amides as Enabling and Cleavable Tethers.
Org Lett
October 2023
Department of Chemistry, Illinois State University, Campus Box 4160, Normal, Illinois 61790-4160, United States.
Silyloxypyrone-based (5+2) cycloadditions were facilitated by amides that allowed for increased reactivity and a pathway for cleaving the tether to afford net intermolecular cycloadducts. Various amides underwent facile cycloaddition, and several experiments revealed steric and electronic factors that accelerate the reaction. -Butyl amides reacted faster than less hindered variants in multiple cases.
View Article and Find Full Text PDFThe case for an oxidopyrylium intermediate in the mechanism of quercetin dioxygenases.
J Inorg Biochem
October 2023
Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, United States of America. Electronic address:
The quercetin dioxygenases (QDOs) are unusual metalloenzymes in that they display ring-opening dioxygenase activity with several different first-row transition metal ions which do not undergo redox changes during turnover. The QDOs are also unique in that the substrate binds as an η-flavonolate rather than the ηbidentate mode seen in all reported model complexes. The flavonol substrates were early examples of excited state intramolecular proton transfer (ESIPT) phenomena, in which photoexcitation causes an H-atom exchange between the adjacent hydroxyl and ketone, generating an oxidopyrylium emissive state.
View Article and Find Full Text PDFSilver-Catalyzed Tandem Cycloisomerization/[5 + 2] Cycloaddition of 3-Cyclopropylideneprop-2-en-1-ones with Oxidopyrylium Ylides to Form Bibridged Benzocycloheptanones.
J Org Chem
July 2023
State Key Laboratory, College of Chemistry, Institute of Elemento-Organic Chemistry, Nankai University, Weijin Road 94, Tianjin 300071, China.
Herein, we report a mild, one-pot method for silver-catalyzed tandem cycloisomerization/[5 + 2] cycloaddition reactions between readily accessible cyclopropyl-tethered allenyl ketones and benzopyranone-derived oxidopyrylium ylides. The reactions proceed a cyclobutene-fused furan intermediate generated by a cycloisomerization/1,2-carbene transfer/ring-expansion cascade. This method, which features an unprecedented formal [5 + 2] cycloaddition, delivers good to excellent yields of structurally complex bibridged benzocycloheptanones bearing a strained cyclobutane ring and an -bridged ring.
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