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1.
alpha-Fluorocarboxylic esters and acids were synthesized in good yields. The corresponding esters and acids were converted to their ketene acetals, and these enol derivatives reacted with AcOF made directly from fluorine. This route circumvents the problems associated with nucleophilic fluorinations such as various eliminations and rearrangements. alpha- and beta-branched carboxylic acid derivatives that cannot be directly fluorinated gave by this electrophilic fluorination the corresponding alpha-fluoro derivatives in good yield. Both the fluorination reaction and the preparation of AcOF are fast and suitable for [18]F incorporation into acids and esters needed for working with PET. alpha-Fluoroibuprofen (20) and methyl 2-fluoro-3,3,3-triphenylpropionate (32) are two examples of this general reaction. 相似文献
2.
Susanna H. Wood Dr. Stephen Etridge Dr. Alan R. Kennedy Prof. Jonathan M. Percy Dr. David J. Nelson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(21):5574-5585
The reaction of enol esters with SelectFluor is facile and leads to the corresponding α-fluoroketones under mild conditions and, as a result, this route is commonly employed for the synthesis of medicinally important compounds such as fluorinated steroids. However, despite the use of this methodology in synthesis, the mechanism of this reaction and the influence of structure on reactivity are unclear. A rigorous mechanistic study of the fluorination of these substrates is presented, informed primarily by detailed and robust kinetic experiments. The results of this study implicate a polar two-electron process via an oxygen-stabilised carbenium species, rather than a single-electron process involving radical intermediates. The structure–reactivity relationships revealed here will assist synthetic chemists in deploying this type of methodology in the syntheses of α-fluoroketones. 相似文献
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The intermediate 6 can be converted into enone 13 using a [2.3]sigmatropic sulfoxide rearrangement as the key transformation. The C-13 hydroxylation of 13 was studied, and found to give 14 (epimeric to guanacastepene A). Examination of silyl enol ethers of 13 demonstrated the ready isomerization of the kinetic silyl enol ether into the more stable thermodynamic silyl enol ether under mild electrophilic reaction conditions. 相似文献
5.
Masaaki Komatsuda Ayane Suto Hiroki Kondo Jr Hiroyuki Takada Kenta Kato Bunnai Saito Junichiro Yamaguchi 《Chemical science》2022,13(3):665
We have discovered a ring-opening fluorination of bicyclic azaarenes. Upon treatment of bicyclic azaarenes such as pyrazolo[1,5-a]pyridines with electrophilic fluorinating agents, fluorination of the aromatic ring is followed by a ring-opening reaction. Although this overall transformation can be classified as an electrophilic fluorination of an aromatic ring, it is a novel type of fluorination that results in construction of tertiary carbon–fluorine bonds. The present protocol can be applied to a range of bicyclic azaarenes, tolerating azines and a variety of functional groups. Additionally, mechanistic studies and enantioselective fluorination have been examined.A ring-opening fluorination of bicyclic azaarenes was developed. Although this overall transformation can be classified as an electrophilic fluorination of aromatics, it is a novel type of fluorination that results in construction of tert-C–F bonds. 相似文献
6.
The direct electrophilic fluorination of unactivated remote tertiary hydrogens is effected by the number, nature and distance of electron-withdrawing groups. The effect of these groups on reducing electron density of the tertiary CH bond seems to be additive. The more remote these groups are from the reaction center, the higher the yield of the fluorination. 相似文献
7.
Novel methods for the facile construction of 3,3-disubstituted and 3, 3-spiro 2H,4H-benzo[e][1,2]thiazine-1,1-diones 8a-h are described. o-Methyl lithiation of N-Boc-o-toluenesulfonamide 6 followed by reaction with a variety of ketones gave the corresponding carbinol sulfonamides 7a-g, which underwent cyclization under acidic (methanesulfonic acid) or neutral (NaI/TMSCl/MeCN) conditions to afford the sultams 8a-h in high yields. The chiral spiro sultams 8g, h were subjected to FClO(3) fluorination to give the N-fluorosultams 11a,b, respectively, which were tested for electrophilic asymmetric fluorination of aryl ketone enolates. As a result, the N-fluorosultam 11a exhibited modest asymmetric inducing abilities with the highest ee, reaching 70% for enantioselective fluorination of the lithium enolate of 2-methyl-1-tetralone. 相似文献
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1,3-Ketoesters and 1,3-diketones react with fluorine gas, using Durham multichannel modular microreactor technology, on a preparatively useful scale. High conversions and yields of monofluorinated products were obtained. A consideration of the mechanism of fluorination of dicarbonyl systems provides a rationale of the scope and limitations of the use of microreactor technology for such direct fluorination processes. We conclude that it is especially appropriate for the fluorination of diketones and ketoesters that exist mainly in the enol form at equilibrium and/or undergo rapid keto-enol interconversion. A one-stage route to fluoroketones from ketoesters was achieved by allowing the crude product mixture obtained from the fluorination of the ketoesters to stand for a period of time before reaction work-up. 相似文献
11.
Robert Szpera Daniel F. J. Moseley Lewis B. Smith Alistair J. Sterling Vronique Gouverneur 《Angewandte Chemie (International ed. in English)》2019,58(42):14824-14848
This Review summarizes advances in fluorination by C(sp2)?H and C(sp3)?H activation. Transition‐metal‐catalyzed approaches championed by palladium have allowed the installation of a fluorine substituent at C(sp2) and C(sp3) sites, exploiting the reactivity of high‐oxidation‐state transition‐metal fluoride complexes combined with the use of directing groups (some transient) to control site and stereoselectivity. The large majority of known methods employ electrophilic fluorination reagents, but methods combining a nucleophilic fluoride source with an oxidant have appeared. External ligands have proven to be effective for C(sp3)?H fluorination directed by weakly coordinating auxiliaries, thereby enabling control over reactivity. Methods relying on the formation of radical intermediates are complementary to transition‐metal‐catalyzed processes as they allow for undirected C(sp3)?H fluorination. To date, radical C?H fluorinations mainly employ electrophilic N?F fluorination reagents but a unique MnIII‐catalyzed oxidative C?H fluorination using fluoride has been developed. Overall, the field of late‐stage nucleophilic C?H fluorination has progressed much more slowly, a state of play explaining why C?H 18F‐fluorination is still in its infancy. 相似文献
12.
Syvret RG Butt KM Nguyen TP Bulleck VL Rieth RD 《The Journal of organic chemistry》2002,67(13):4487-4493
In the present work, the electrophile equivalents Cl+, Br+, SCN+, and NO2+ are generated from their respective sodium, potassium, and in some cases ammonium salts (M+X-) by reaction with Selectfluor electrophilic fluorination agent in acetonitrile solution at room temperature. These generated electrophilic species subsequently react in situ with a variety of aromatic substrates containing one or more substituent groups including H, F, Cl, CH3, COOH, C(O)CH3, NO2, and OR' and NR'R' ' where R' and R' ' are H or CH3. The resulting substitution products are, in most cases, isolable as pure compounds in high yield. Variations in the process include the use of other anions, electrophilic fluorination agents, and solvents. 相似文献
13.
The Selectfluor™ electrophilic fluorination agent 1 is now produced in multi-ton per year quantities and is one of only a few fluorine-containing fine chemicals that are produced by direct fluorination with F2 on an industrial scale. From the initial concept of the “ideal fluorination agent” to the present day industrial scale production of Selectfluor™, the route to the successful commercialization included a series of critical steps. A chronological account of the road to commercialization of Selectfluor™, noting the important product development factors, is provided herein. 相似文献
14.
Jesús Ramírez 《Tetrahedron letters》2007,48(22):3841-3845
Tandem catalytic diboration/fluorination/imination of arylacetylenes leads to the formation of α,α-difluoroimines, where the adjacent CN and C-F2 bonds are formed simultaneously. The convenient one-pot protocol involves a Pt(0)-catalyzed diboration of terminal or internal arylalkynes followed by electrophilic fluorination with Selectfluor in the presence of primary amines and a dehydrating agent. A plausible mechanism for the three consecutive steps (diboration/fluorination/imination) is suggested in accordance with the electronic properties of the substrates. Alkynes/catalytic diboration/alkenyl diboronate esters/Selectfluor/electrophilic fluorination/α,α-difluoroimines. 相似文献
15.
Marcus Baumann 《Tetrahedron》2009,65(33):6611-391
The safe and reliable use of various fluorination methods including nucleophilic fluorination (DAST), trifluoromethylation (Ruppert's reagent) and electrophilic fluorination (Selectfluor®) in a continuous-flow microreactor is reported. Special attention was given to the use of in-line scavenging procedures in order to obtain clean products without the need for further purification. 相似文献
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G. I. Borodkin P. A. Zaikin M. M. Shakirov V. G. Shubin 《Russian Journal of Organic Chemistry》2007,43(10):1451-1459
Kinetic isotope effects H/D in electrophilic fluorination of aromatic compounds with NF-reagents were investigated. The small values of k H/k D (0.86–1.00) are in agreement with the polar reaction mechanism where the Wheland complex decomposition is not the limiting stage. The fluorination of 1,3,5-trideuterobenzene was established by 1H and 19F NMR spectroscopy to occur with a 1,2-migration of a hydrogen (deuterium) atom. The analysis of Brown-Stock relationship demonstrated that the activity of NF-reagents exceeded that of many known electrophilic systems including halogenation, but it was essentially less than the activity of elemental fluorine. 相似文献
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The interaction of the nitroxide radical traps (Tempo and Dmpo) and radicals produced in the electrophilic fluorination of olefins (styrene and alpha-methylstyrene) and Selectfluor (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octanebis(tetrafluoroborate) (F-TEDA-BF(4)) (1)) was investigated by electrospray ionization mass spectrometry (ESI-MS). Tempo succeeded in intercepting the radical cationic intermediates and the radical adduct ions were detected at m/z 260 (for styrene) and m/z 274 (for alpha-methylstyrene). Dmpo could also intercept the fluorine radical and radical adduct ions were detected at m/z 131, 132 and 152. The interception of the radical cationic intermediates and fluorine radical is good evidence for the presence of a single-electron transfer mechanism in the electrophilic fluorination. 相似文献
18.
Christoph Fricke Kristina Deckers Prof. Dr. Franziska Schoenebeck 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(42):18876-18881
While halogenation is of key importance in synthesis and radioimaging, the currently available repertoire is largely designed to introduce a single halogen per molecule. This report makes the selective introduction of several different halogens accessible. Showcased here is the privileged stability of nontoxic aryl germanes under harsh fluorination conditions (that allow selective fluorination in their presence), while displaying superior reactivity and functional-group tolerance in electrophilic iodinations and brominations, outcompeting silanes or boronic esters under rapid and additive-free conditions. Mechanistic experiments and computational studies suggest a concerted electrophilic aromatic substitution as the underlying mechanism. 相似文献
19.
Synthesis of Fluorinated Heteroaromatics through Formal Substitution of a Nitro Group by Fluorine under Transition‐Metal‐Free Conditions 下载免费PDF全文
Ran‐Ning Guo Xian‐Feng Cai Lei Shi Zhang‐Pei Chen Prof. Yong‐Gui Zhou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(27):8343-8346
An efficient and transition‐metal‐free approach was developed to access a series of fluorinated heteroaromatics in moderate to excellent yields. This one‐pot procedure features a triple‐relay transformation of rapid dearomatization, fluorination, and rearomatization processes, which represents a conceptually novel strategy of combining partial hydrogenation and electrophilic fluorination. 相似文献
20.
The first enantiopure N-fluoro quaternary ammonium salts of cinchona alkaloids as enantioselective fluorinating agents are reported. A one-step transfer-fluorination on the naturally occurring cinchona alkaloids gave the fluorinating agents F-CA-BF(4). This new generation of fluorinating agents exhibited asymmetric induction up to 61% on fluorination of enolates and silyl enol ethers of 2-methyl-1-tetralone. 相似文献