1194-02-1Relevant articles and documents
Theoretical Design and Calculation of a Crown Ether Phase-Transfer-Catalyst Scaffold for Nucleophilic Fluorination Merging Two Catalytic Concepts
Carvalho, Nathália F.,Pliego, Josefredo R.
, p. 8455 - 8463 (2016)
Fluorinated organic molecules are playing an increased role in the area of pharmaceuticals and agrochemicals. This fact demands the development of efficient catalytic fluorination processes. In this paper, we have designed a new crown ether with four hydroxyl groups strategically positioned. The catalytic activity of this basic scaffold was investigated with high levels of electronic structure theory, such as the ONIOM approach combining MP4 and MP2 methods. On the basis of the calculations, this new structure is able to solubilize potassium fluoride in toluene solution much more efficiently than 18-crown-6 (18C6). In addition, the strong interaction of the new catalyst with the SN2 transition state leads to a very important catalytic effect, with a predicted free energy barrier of 23.3 kcal mol-1 for potassium fluoride plus ethyl bromide reaction model. Compared with experimental data and previous theoretical studies, this new catalyst is 104 times more efficient than 18C6 for nucleophilic fluorination of alkyl halides. The catalysis is predicted to be selective, leading to 97% of fluorination and only 3% of elimination. Catalytic fluorination of the aromatic ring has also been investigated, and although the catalyst is less efficient in this case, our analysis has indicated further development of this strategy can lead to more efficient catalysis.
POLYMER-SUPPORTED AMINOPYRIDINIUM SALTS AS VERSATILE CATALYSTS FOR THE SYNTHESIS OF ARYL FLUORIDES
Yoshida, Yasuo,Kimura, Yoshizaku,Tomoi, Masao
, p. 7199 - 7202 (1989)
Immobilized N-alkylaminopyridinium salts on divinylbenzene crosslinked polystyrene gel was reusable at least 8 times on the reaction of 4-chloronitrobenzene with anhydrous potassium fluoride in tetrahydrothiophene 1,1-dioxide to give 4-fluoronitrobenzene in high yield.The immobilized catalyst was also successfully used for a synthesis of several aryl fluorides in good yields.
Efficient synthesis of aryl fluorides
Anbarasan, Pazhamalai,Neumann, Helfried,Beller, Matthias
, p. 2219 - 2222 (2010)
Chemical Equation Presented Creating C-F bonds: A novel electrophilic fluorination of aryl and heteroaryl Crignard reagents has been discovered and was used for the efficient synthesis of various aryl fluoride derivatives (see picture; THF = tetrahydrofuran).
Sensitization-initiated electron transferviaupconversion: mechanism and photocatalytic applications
Glaser, Felix,Kerzig, Christoph,Wenger, Oliver S.
, p. 9922 - 9933 (2021)
Sensitization-initiated electron transfer (SenI-ET) describes a recently discovered photoredox strategy that relies on two consecutive light absorption events, triggering a sequence of energy and electron transfer steps. The cumulative energy input from two visible photons gives access to thermodynamically demanding reactions, which would be unattainable by single excitation with visible light. For this reason, SenI-ET has become a very useful strategy in synthetic photochemistry, but the mechanism has been difficult to clarify due to its complexity. We demonstrate that SenI-ET can operateviasensitized triplet-triplet annihilation upconversion, and we provide the first direct spectroscopic evidence for the catalytically active species. In our system comprised offac-[Ir(ppy)3] as a light absorber, 2,7-di-tert-butylpyrene as an annihilator, andN,N-dimethylaniline as a sacrificial reductant, all photochemical reaction steps proceed with remarkable rates and efficiencies, and this system is furthermore suitable for photocatalytic aryl dehalogenations, pinacol couplings and detosylation reactions. The insights presented here are relevant for the further rational development of photoredox processes based on multi-photon excitation, and they could have important implications in the greater contexts of synthetic photochemistry and solar energy conversion.
Copper-Mediated Oxidative Fluorination of Aryl Stannanes with Fluoride
Gamache, Raymond F.,Waldmann, Christopher,Murphy, Jennifer M.
, p. 4522 - 4525 (2016)
A regiospecific method for the oxidative fluorination of aryl stannanes using tetrabutylammonium triphenyldifluorosilicate (TBAT) and copper(II) triflate is described. This reaction is robust, uses readily available reagents, and proceeds via a stepwise protocol under mild conditions (60 °C, 3.2 h). Broad functional group tolerance, including arenes containing protic and nucleophilic groups, is demonstrated.
Cu(OTf)2-mediated fluorination of aryltrifluoroborates with potassium fluoride
Ye, Yingda,Schimler, Sydonie D.,Hanley, Patrick S.,Sanford, Melanie S.
, p. 16292 - 16295 (2013)
This Communication describes the Cu(OTf)2-mediated fluorination of aryltrifluoroborates with KF. The reaction proceeds under mild conditions (at 60 C over 20 h) and shows a broad substrate scope and functional group tolerance. The Cu is proposed to play two separate roles in this transformation: (1) as a mediator for the aryl-F coupling and (2) as an oxidant for accessing a proposed CuIII(aryl)(F) intermediate.
Fluorodediazoniation in ionic liquid solvents: New life for the Balz-Schiemann reaction
Laali, Kenneth K.,Gettwert, Volker J.
, p. 31 - 34 (2001)
Drawbacks associated with the classic Balz-Schiemann reaction are eliminated in a series of examples by conducting fluorodediazoniation in ionic liquid solvents, thus opening up a new horizon for a much in demand process.
NUCLEOPHILIC AROMATIC SUBSTITUTION OF ACTIVATED CATIONIC GROUPS BY 18F-LABELED FLUORIDE. A USEFUL ROUTE TO NO-CARRIER-ADDED (NCA) 18F-LABELED ARYL FLUORIDES
Angelini, G.,Speranza, M.,Wolf, A. P.,Shiue, C.-Y.
, p. 177 - 192 (1985)
A method is described for the rapid preparation of no-carrier-added (NCA) 18F-labeled aryl fluorides by treatment of the corresponding aryltrimethylammonium perchlorates with 18F-labeled fluoride in DMSO.The basic features of the 18F-for-+NMe3 displacement process are evaluated as a function of the experimental variables and compared with related substitution routes to NCA 18F-labeled aryl fluorides.The relative nucleofugicity of the ammonium group in the nucleophilic substitution reactions surpasses that of the best neutral leaving groups, including NO2 and F itself.In contrast, radiofluoride incorporation into aromatic rings via other cationic substrates, such as aryldimethylsulfonium perchlorates, is prevented by the fast methyl group transfer from the starting compound to the nucleophiles present.The use of the ammonium function as a leaving group in nucleophilic substitutions by 18F- may give access to the rapid preparation of novel NCA 18F-radiopharmaceuticals by facilitating the synthesis and the purification of their labeled precursors.
Studying regioisomer formation in the pd-catalyzed fluorination of aryl triflates by deuterium labeling
Milner, Phillip J.,Kinzel, Tom,Zhang, Yong,Buchwald, Stephen L.
, p. 15757 - 15766 (2014)
Isotopic labeling has been used to determine that a portion of the desired product in the Pd-catalyzed fluorination of electron-rich, non-ortho-substituted aryl triflates results from direct C-F cross-coupling. In some cases, formation of a Pd-aryne intermediate is responsible for producing undesired regioisomers. The generation of the Pd-aryne intermediate occurs primarily via ortho-deprotonation of a L·Pd(Ar)OTf (L = biaryl monophosphine) species by CsF and thus competes directly with the transmetalation step of the catalytic cycle. Deuterium labeling studies were conducted with a variety of aryl triflates.
Deaminative Fluorination of Anilines with Silicon Tetrafluoride: Utility of Silicon Tetrafluoride as a Fluorine Source
Tamura, Masanori,Shibakami, Motonari,Sekiya, Akira
, p. 725 - 727 (1998)
Application of silicon tetrafluoride to deaminative fluorination of anilines as a fluorine source is investigated. A diazotization of anilines proceeds with silicon tetrafluoride and tbutyl nitrite under mild condition and the following fluorodediazoniation affords fluoroarenes in good yields.
