Electrophilic Cyclizations of 2‐Fluoroalk‐3‐yn‐1‐ones: Room‐Temperature Synthesis of Diversely 2,5‐Disubstituted 3,4‐Fluorohalofurans

Li, Yan; Wheeler, Kraig A.; Dembiński, Roman

doi:10.1002/ejoc.201100344

Cited by 18 publications

(8 citation statements)

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“…Since such type of gold-catalyzed transformations involved the intermediacy of vinyl gold species, the authors envisioned that, in the presence of an electrophilic halogen source and under properly reaction conditions, a halodeauration event would render the corresponding 3,4-dihalofurans, opening the door for the preparation of entirely diverse substituted 3-fluorofurans 15 . , However, the electron-withdrawing effect imparted by fluorine atom diminishes the nucleophilicity of the corresponding vinyl gold intermediate toward the electrophilic reagent, thus preventing halocyclization unless a cocatalyst is used. Finally, gold-assisted halocyclization of ynones 13 was accomplished in the presence of 20 mol % of ZnBr 2 using NIS or NBS as the electrophilic source and AuCl as the catalyst (Scheme , eq 2).…”

Section: Fluorinated Starting Materials In Gold-catalyzed Reactionsmentioning

confidence: 99%

Fluorine and Gold: A Fruitful Partnership

2016

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Gold-catalyzed reactions have witnessed an exponential growth in the past decade. When the unique modes of activation exhibited by gold species meet species with either fluorinated building blocks or fluorinating reagents, new opportunities arise for the development of new methodologies in fluoroorganic chemistry. Indeed, gold and fluorine truly formed a very fruitful partnership, and different types of reactivity emerged from their combination. This review gives an overview of such endeavors. The special properties imparted by fluorine to organic molecules have been exploited in gold-catalyzed processes, allowing for the generation of unprecedented fluorinated chemical entities. Thus, the interaction of gold salts with fluorinated building blocks has been revised. In a second section, recent developments in gold-catalyzed nucleophilic fluorinations have been covered. The development of new gold catalysts that stabilize the Au-F bond as well as recent mechanistic studies in the field raised the interest of these types of methodologies for the generation of new C-F bonds. The use of electrophilic fluorine sources enabled new modes of gold catalysis. The incorporation of Selectfluor as an external oxidant constituted a new paradigm in gold chemistry, incorporating the elusive Au(I)/Au(III) redox couple in gold-catalyzed transformations. This strategy provided access to both new fluorinated chemical entities and nonfluorinated derivatives by means of coupling reactions. Those topics have been reviewed in the last two sections.

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Section: Fluorinated Starting Materials In Gold-catalyzed Reactionsmentioning

confidence: 99%

Fluorine and Gold: A Fruitful Partnership

2016

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“…However, the incidence of the reaction (albeit slow) with sole N-iodo-or N-bromosuccinimide, indicates that the electrophilic halogen is capable of acting by itself (Table 5 entry 1 and ref. 25). Also, the lack of non-halogenated fluorofurans formation (within detection limit of 1 H NMR), when the cyclization reaction was carried out in the presence of gold/NXS, may suggest that gold may not act as the cyclization catalyst but rather as the activator of the NXS.…”

Section: Resultsmentioning

confidence: 99%

“…The better stability of formed bromofuran towards gold catalyst along with the milder halogenation reagent (NBS) provided an advantage over the initial optimization results acquired for the iodocyclization reaction. 25 The bromination reactions were cleaner; essentially since only the product and unreacted substrate were observed. Bromofurans, as compared to iodo derivatives, are less reactive.…”

Section: Resultsmentioning

confidence: 99%

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Room temperature syntheses of entirely diverse substituted β-fluorofurans

Wheeler

Dembiński

2012

Org. Biomol. Chem.

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Synthesis of highly substituted 3-fluorofurans is reported. The sequence began with preparation of tert-butyldimethylsilyl alk-1-en-3-yn-1-yl ethers from 1,4-disubstituted alk-3-yn-1-ones. Subsequent fluorination of alkenynyl silyl ethers with Selectfluor gave 2-fluoroalk-3-yn-1-ones in almost quantitative yield. Subsequent 5-endo-dig cyclizations using chlorotriphenylphosphine gold(I)/silver trifluoromethanesulfonate (5/5 mol%), N-bromo- or N-iodosuccinimide and gold(I) chloride/zinc bromide (5/20 mol%), all at room temperature, provided a facile method for the generation of substituted 3-fluoro-, 3-bromo-4-fluoro-, and 3-fluoro-4-iodofurans in good yields. Also, 2,2-difluoroalk-3-yn-1-ones were prepared by fluorination of alk-3-yn-1-ones under organocatalytic conditions. The structures of (Z)-tert-butyldimethylsilyl but-1-en-3-yn-1-yl ether, 3-bromo-4-fluorofuran, and 3-fluoro-4-(phenylethynyl)furan were confirmed by X-ray crystallography.

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“…77 In 2011, the same group described the Au(I)/Zn(II)-catalyzed halocyclization of 2-fluoro-3-alkynyl ketones in the presence of N -iodo- or N -bromosuccinimide to produce 3,4-fluorohalofurans under mild reaction conditions. 78 …”

Section: Synthesis Of Furansmentioning

confidence: 99%