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18 pages, 17963 KiB

Open AccessArticle

Mechanochemical Synthesis of Fluorinated Imines

by Karolina Ciesielska, Marcin Hoffmann, Maciej Kubicki and Donata Pluskota-Karwatka

Molecules 2022, 27(14), 4557; https://doi.org/10.3390/molecules27144557 - 17 Jul 2022

Cited by 3 | Viewed by 2224

Abstract

A number of imines, including 12 new compounds, previously not reported in the literature, derived from variously fluorinated benzaldehydes and different anilines or chiral benzylamines were synthesized by a solvent-free mechanochemical method, which was based on the manual grinding of equimolar amounts of [...] Read more.

A number of imines, including 12 new compounds, previously not reported in the literature, derived from variously fluorinated benzaldehydes and different anilines or chiral benzylamines were synthesized by a solvent-free mechanochemical method, which was based on the manual grinding of equimolar amounts of the substrates at the room temperature. In a very short reaction time of only 15 min, the method produced the expected products with good-to-excellent yields. The yields were comparable or significantly higher than those reported in the literature for the imines synthesized by other methods. Importantly, the conditions used for the reactions with aniline derivatives also resulted in the high yields of imines obtained from chiral benzylamines, and can be extended to the synthesis with other similar amines. Structures of all imines were confirmed by NMR spectroscopy: ¹H, ¹³C and ¹⁹F. For four compounds, X-ray structures were also obtained. The synthetic approach presented in this paper contributes to the prevention of environmental pollution and can be easily extended for larger-scale syntheses. The mechanochemical solvent-free method provides a convenient strategy particularly useful for the preparation of fluorinated imines being versatile intermediates or starting material in the synthesis of drugs and other fine chemicals. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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18 pages, 4217 KiB

Open AccessArticle

Naphthalene vs. Benzene as a Transmitting Moiety: Towards the More Sensitive Trifluoromethylated Molecular Probes for the Substituent Effects

by Adam Sokół, Henryk Koroniak, Marcin Hoffmann and Tomasz Siodła

Molecules 2022, 27(13), 4173; https://doi.org/10.3390/molecules27134173 - 29 Jun 2022

Cited by 1 | Viewed by 1942

Abstract

The application of DFT computational method (B3LYP/6-311++G(d,p)) to mono- and poly(CF₃)substituted naphthalene derivatives helps to study changes in the electronic properties of these compounds under the influence of 11 substituents (-Br, -CF₃, -CH₃, -CHO, -Cl, -CN, -F, [...] Read more.

The application of DFT computational method (B3LYP/6-311++G(d,p)) to mono- and poly(CF₃)substituted naphthalene derivatives helps to study changes in the electronic properties of these compounds under the influence of 11 substituents (-Br, -CF₃, -CH₃, -CHO, -Cl, -CN, -F, -NH₂, -NMe₂, -NO₂, and -OH) to confront substituent effects in naphthalene with an analogous situation in benzene. This paper shows the dependencies of theoretically calculated SESE (Substituent Effect Stabilization Energy) values on empirically determined, well-defined Hammett-type constants (σ_p, σ_m, R, and F). Described poly(CF₃)substituted derivatives of naphthalene are, so far, the most sensitive molecular probes for the substituent effects in the aromatic system. The presence of the trifluoromethyl groups of such an expressive nature significantly increases the sensitivity of the SESE to changes caused by another substitution. Further, the more -CF₃ groups are attached to the naphthalene ring, the more sensitive the probe is. Certain groups of probes show additivity of sensitivity: the obtained sensitivity relates to the sum of the sensitivities of the mono(CF₃)substituted probes. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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8 pages, 9075 KiB

Open AccessArticle

Nucleophilic Radiofluorination Using Tri-tert-Butanol Ammonium as a Bifunctional Organocatalyst: Mechanism and Energetics

by Young-Ho Oh, Sandip S. Shinde and Sungyul Lee

Molecules 2022, 27(3), 1044; https://doi.org/10.3390/molecules27031044 - 3 Feb 2022

Cited by 1 | Viewed by 1668

Abstract

We present a quantum chemical analysis of the ¹⁸F-fluorination of 1,3-ditosylpropane, promoted by a quaternary ammonium salt (tri-(tert-butanol)-methylammonium iodide (TBMA-I) with moderate to good radiochemical yields (RCYs), experimentally observed by Shinde et al. We obtained the mechanism of the S [...] Read more.

We present a quantum chemical analysis of the ¹⁸F-fluorination of 1,3-ditosylpropane, promoted by a quaternary ammonium salt (tri-(tert-butanol)-methylammonium iodide (TBMA-I) with moderate to good radiochemical yields (RCYs), experimentally observed by Shinde et al. We obtained the mechanism of the S_N2 process, focusing on the role of the –OH functional groups facilitating the reactions. We found that the counter-cation TBMA⁺ acts as a bifunctional promoter: the –OH groups function as a bidentate ‘anchor’ bridging the nucleophile [¹⁸F]F⁻ and the –OTs leaving group or the third –OH. These electrostatic interactions cooperate for the formation of the transition states of a very compact configuration for facile S_N2 ¹⁸F-fluorination. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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20 pages, 18330 KiB

Open AccessArticle

Unsymmetrical Trifluoromethyl Methoxyphenyl β-Diketones: Effect of the Position of Methoxy Group and Coordination at Cu(II) on Biological Activity

by Liliya A. Khamidullina, Igor S. Puzyrev, Gennady L. Burygin, Pavel V. Dorovatovskii, Yan V. Zubavichus, Anna V. Mitrofanova, Victor N. Khrustalev, Tatiana V. Timofeeva, Pavel A. Slepukhin, Polina D. Tobysheva, Alexander V. Pestov, Euro Solari, Alexander G. Tskhovrebov and Valentine G. Nenajdenko

Molecules 2021, 26(21), 6466; https://doi.org/10.3390/molecules26216466 - 26 Oct 2021

Cited by 7 | Viewed by 3214

Abstract

Copper(II) complexes with 1,1,1-trifluoro-4-(4-methoxyphenyl)butan-2,4-dione (HL1) were synthesized and characterized by elemental analysis, FT-IR spectroscopy, and single crystal X-ray diffraction. The biological properties of HL1 and cis-[Cu(L1)₂(DMSO)] (3) were examined against Gram-positive and Gram-negative [...] Read more.

Copper(II) complexes with 1,1,1-trifluoro-4-(4-methoxyphenyl)butan-2,4-dione (HL1) were synthesized and characterized by elemental analysis, FT-IR spectroscopy, and single crystal X-ray diffraction. The biological properties of HL1 and cis-[Cu(L1)₂(DMSO)] (3) were examined against Gram-positive and Gram-negative bacteria and opportunistic unicellular fungi. The cytotoxicity was estimated towards the HeLa and Vero cell lines. Complex 3 demonstrated antibacterial activity towards S. aureus comparable to that of streptomycin, lower antifungal activity than the ligand HL1 and moderate cytotoxicity. The bioactivity was compared with the activity of compounds of similar structures. The effect of changing the position of the methoxy group at the aromatic ring in the ligand moiety of the complexes on their antimicrobial and cytotoxic activity was explored. We propose that complex 3 has lower bioavailability and reduced bioactivity than expected due to strong intermolecular contacts. In addition, molecular docking studies provided theoretical information on the interactions of tested compounds with ribonucleotide reductase subunit R2, as well as the chaperones Hsp70 and Hsp90, which are important biomolecular targets for antitumor and antimicrobial drug search and design. The obtained results revealed that the complexes displayed enhanced affinity over organic ligands. Taken together, the copper(II) complexes with the trifluoromethyl methoxyphenyl-substituted β-diketones could be considered as promising anticancer agents with antibacterial properties. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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8 pages, 19101 KiB

Open AccessArticle

Origin of Salt Effects in S_N2 Fluorination Using KF Promoted by Ionic Liquids: Quantum Chemical Analysis

by Young-Ho Oh and Sungyul Lee

Molecules 2021, 26(19), 5738; https://doi.org/10.3390/molecules26195738 - 22 Sep 2021

Cited by 2 | Viewed by 1641

Abstract

Quantum chemical analysis is presented, motivated by Grée and co-workers’ observation of salt effects [Adv. Synth. Catal. 2006, 348, 1149–1153] for S_N2 fluorination of KF in ionic liquids (ILs). We examine the relative promoting capacity of KF in [bmim]PF₆ vs. [...] Read more.

Quantum chemical analysis is presented, motivated by Grée and co-workers’ observation of salt effects [Adv. Synth. Catal. 2006, 348, 1149–1153] for S_N2 fluorination of KF in ionic liquids (ILs). We examine the relative promoting capacity of KF in [bmim]PF₆ vs. [bmim]Cl by comparing the activation barriers of the reaction in the two ILs. We also elucidate the origin of the experimentally observed additional rate acceleration in IL [bmim]PF₆ achieved by adding KPF₆. We find that the anion PF₆⁻ in the added salt acts as an extra Lewis base binding to the counter-cation K⁺ to alleviate the strong Coulomb attractive force on the nucleophile F⁻, decreasing the Gibbs free energy of activation as compared with that in its absence, which is in good agreement with experimental observations of rate enhancement. We also predict that using 2 eq. KF together with an eq. KPF₆ would further activate S_N2 fluorination Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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12 pages, 2463 KiB

Open AccessArticle

Radiosynthesis of 5-[¹⁸F]Fluoro-1,2,3-triazoles through Aqueous Iodine–[¹⁸F]Fluorine Exchange Reaction

by Xiang Zhang, Falguni Basuli, Sameh Abdelwahed, Tadhg Begley and Rolf Swenson

Molecules 2021, 26(18), 5522; https://doi.org/10.3390/molecules26185522 - 11 Sep 2021

Cited by 3 | Viewed by 2398

Abstract

In this report, a simple and efficient process to achieve fluorine-18-labeled 1,2,3-triazole is reported. The heteroaromatic radiofluorination was successfully achieved through an iodine–fluorine-18 exchange in an aqueous medium requiring only trace amounts of base and no azeotropic drying of fluorine-18. This methodology was [...] Read more.

In this report, a simple and efficient process to achieve fluorine-18-labeled 1,2,3-triazole is reported. The heteroaromatic radiofluorination was successfully achieved through an iodine–fluorine-18 exchange in an aqueous medium requiring only trace amounts of base and no azeotropic drying of fluorine-18. This methodology was optimized on a model reaction and further validated on multiple 1,2,3-triazole substrates with 18–60% radiochemical conversions. Using this strategy—the radiosynthesis of a triazole-based thiamin analogue—a potential positron emission tomography (PET) probe for imaging thiamin-dependent enzymes was synthesized with 10–16% isolated radiochemical yield (RCY) in 40 min (uncorrected, n > 5). Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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19 pages, 2424 KiB

Open AccessFeature PaperArticle

2-Aryl-6-Polyfluoroalkyl-4-Pyrones as Promising R^F-Building-Blocks: Synthesis and Application for Construction of Fluorinated Azaheterocycles

by Sergey A. Usachev, Diana I. Nigamatova, Daria K. Mysik, Nikita A. Naumov, Dmitrii L. Obydennov and Vyacheslav Y. Sosnovskikh

Molecules 2021, 26(15), 4415; https://doi.org/10.3390/molecules26154415 - 21 Jul 2021

Cited by 7 | Viewed by 2861

Abstract

A convenient and general method for the direct synthesis of 2-aryl-6-(trifluoromethyl)-4-pyrones and 2-aryl-5-bromo-6-(trifluoromethyl)-4-pyrones has been developed on the basis of one-pot oxidative cyclization of (E)-6-aryl-1,1,1-trifluorohex-5-ene-2,4-diones via a bromination/dehydrobromination approach. This strategy was also applied for the preparation of 2-phenyl-6-polyfluoroalkyl-4-pyrones and their [...] Read more.

A convenient and general method for the direct synthesis of 2-aryl-6-(trifluoromethyl)-4-pyrones and 2-aryl-5-bromo-6-(trifluoromethyl)-4-pyrones has been developed on the basis of one-pot oxidative cyclization of (E)-6-aryl-1,1,1-trifluorohex-5-ene-2,4-diones via a bromination/dehydrobromination approach. This strategy was also applied for the preparation of 2-phenyl-6-polyfluoroalkyl-4-pyrones and their 5-bromo derivatives. Conditions of chemoselective enediones bromination were found and the key intermediates of the cyclization of bromo-derivatives to 4-pyrones were characterized. Synthetic application of the prepared 4-pyrones has been demonstrated for the construction of biologically important CF₃-bearing azaheterocycles, such as pyrazoles, pyridones, and triazoles. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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17 pages, 2015 KiB

Open AccessArticle

Base-Mediated Claisen Rearrangement of CF₃-Containing Bisallyl Ethers

by Yoko Hamada, Rio Matsunaga, Tomoko Kawasaki-Takasuka and Takashi Yamazaki

Molecules 2021, 26(14), 4365; https://doi.org/10.3390/molecules26144365 - 19 Jul 2021

Viewed by 2134

Abstract

We have previously clarified that the strongly electron-withdrawing CF₃ group nicely affected the base-mediated proton shift of CF₃-containing propargylic or allylic alcohols to afford the corresponding α,β-unsaturated or saturated ketones, respectively, which was applied this time to the Claisen rearrangement [...] Read more.

We have previously clarified that the strongly electron-withdrawing CF₃ group nicely affected the base-mediated proton shift of CF₃-containing propargylic or allylic alcohols to afford the corresponding α,β-unsaturated or saturated ketones, respectively, which was applied this time to the Claisen rearrangement after O-allylation of the allylic alcohols with a CF₃ group, followed by isomerization to the corresponding allyl vinyl ethers via the proton shift, enabling the desired rearrangement in a tandem fashion, or in a stepwise manner, the latter of which was proved to have attained an excellent diastereoselectivity with the aid of a palladium catalyst. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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28 pages, 5620 KiB

Open AccessArticle

An Easy Synthesis of Monofluorinated Derivatives of Pyrroles from β-Fluoro-β-Nitrostyrenes

by Alexander S. Aldoshin, Andrey A. Tabolin, Sema L. Ioffe and Valentine G. Nenajdenko

Molecules 2021, 26(12), 3515; https://doi.org/10.3390/molecules26123515 - 9 Jun 2021

Cited by 2 | Viewed by 2058

Abstract

The catalyst-free conjugate addition of pyrroles to β-Fluoro-β-nitrostyrenes was investigated. The reaction was found to proceed under solvent-free conditions to form 2-(2-Fluoro-2-nitro-1-arylethyl)-1H-pyrroles. The effectiveness of this approach was demonstrated through the preparation of a series of the target products in a [...] Read more.

The catalyst-free conjugate addition of pyrroles to β-Fluoro-β-nitrostyrenes was investigated. The reaction was found to proceed under solvent-free conditions to form 2-(2-Fluoro-2-nitro-1-arylethyl)-1H-pyrroles. The effectiveness of this approach was demonstrated through the preparation of a series of the target products in a quantitative yield. The kinetics of a conjugate addition of pyrrole was studied in detail to reveal the substituent effect and activation parameters of the reaction. The subsequent base-induced elimination of nitrous acid afforded a series of novel 2-(2-Fluoro-1-arylvinyl)-1H-pyrroles prepared in up to an 85% isolated yield. The two-step sequence herein proposed is an indispensable alternative to a direct reaction with elusive and unstable 1-Fluoroacetylenes. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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12 pages, 18384 KiB

Open AccessArticle

Photoredox Catalyzed Dealkylative Aromatic Halogen Substitution with Tertiary Amines

by Dmitry L. Lipilin, Alexander E. Frumkin, Alexey Y. Tyurin, Vitalij V. Levin and Alexander D. Dilman

Molecules 2021, 26(11), 3323; https://doi.org/10.3390/molecules26113323 - 1 Jun 2021

Cited by 3 | Viewed by 3348

Abstract

A reaction of aromatic halides bearing electron-withdrawing groups with tertiary amines in the presence of an iridium catalyst under blue light irradiation is described. Products of the aromatic substitution of the halide by the dialkylamino fragment are obtained. The interaction of aryl radicals [...] Read more.

A reaction of aromatic halides bearing electron-withdrawing groups with tertiary amines in the presence of an iridium catalyst under blue light irradiation is described. Products of the aromatic substitution of the halide by the dialkylamino fragment are obtained. The interaction of aryl radicals with tertiary amines to generate zwitterionic radical species is believed to be the key factor responsible for the reaction efficiency. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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11 pages, 2985 KiB

Open AccessArticle

Unexpected Radical Telomerisation of Vinylidene Fluoride with 2-Mercaptoethanol

by Michel Duc, Bernard Boutevin and Bruno Ameduri

Molecules 2021, 26(11), 3082; https://doi.org/10.3390/molecules26113082 - 21 May 2021

Cited by 2 | Viewed by 1952

Abstract

The radical telomerisation of vinylidene fluoride (VDF) with 2-mercaptoethanol as chain transfer agent (CTA) was studied to synthesise fluorinated telomers which bear a hydroxy end-group, such as H(VDF)_nS(CH₂)₂OH, under thermal (di-tert-butyl peroxide as the initiator) [...] Read more.

The radical telomerisation of vinylidene fluoride (VDF) with 2-mercaptoethanol as chain transfer agent (CTA) was studied to synthesise fluorinated telomers which bear a hydroxy end-group, such as H(VDF)_nS(CH₂)₂OH, under thermal (di-tert-butyl peroxide as the initiator) or photochemical initiations. A careful structural study of a typical H-VDF-S(CH₂)₂OH telomer was performed by ¹H and ¹⁹F NMR spectroscopy. These analytical methods allowed us to explore the selective addition of the thiyl radical onto the hydrogenated side of VDF, and the telomer containing one VDF unit was obtained selectively. Surprisingly, for higher [VDF]_o initial concentrations, a monoadduct telomer was produced as well as PVDF homopolymer. This feature was related to the fast consumption of the CTA. The kinetics of radical telomerisation led to a quite high transfer constant of the CTA (40 at 140 °C) that evidences the formation of a monoadduct as the only telomer formed. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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27 pages, 826 KiB

Open AccessArticle

Cu-Catalyzed Arylation of Bromo-Difluoro-Acetamides by Aryl Boronic Acids, Aryl Trialkoxysilanes and Dimethyl-Aryl-Sulfonium Salts: New Entries to Aromatic Amides

by Satenik Mkrtchyan, Michał Jakubczyk, Suneel Lanka, Michael Pittelkow and Viktor O. Iaroshenko

Molecules 2021, 26(10), 2957; https://doi.org/10.3390/molecules26102957 - 16 May 2021

Cited by 7 | Viewed by 3924

Abstract

We describe a mechanism-guided discovery of a synthetic methodology that enables the preparation of aromatic amides from 2-bromo-2,2-difluoroacetamides utilizing a copper-catalyzed direct arylation. Readily available and structurally simple aryl precursors such as aryl boronic acids, aryl trialkoxysilanes and dimethyl-aryl-sulfonium salts were used as [...] Read more.

We describe a mechanism-guided discovery of a synthetic methodology that enables the preparation of aromatic amides from 2-bromo-2,2-difluoroacetamides utilizing a copper-catalyzed direct arylation. Readily available and structurally simple aryl precursors such as aryl boronic acids, aryl trialkoxysilanes and dimethyl-aryl-sulfonium salts were used as the source for the aryl substituents. The scope of the reactions was tested, and the reactions were insensitive to the electronic nature of the aryl groups, as both electron-rich and electron-deficient aryls were successfully introduced. A wide range of 2-bromo-2,2-difluoroacetamides as either aliphatic or aromatic secondary or tertiary amides were also reactive under the developed conditions. The described synthetic protocols displayed excellent efficiency and were successfully utilized for the expeditious preparation of diverse aromatic amides in good-to-excellent yields. The reactions were scaled up to gram quantities. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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12 pages, 22117 KiB

Open AccessArticle

Systematic Studies on the Effect of Fluorine Atoms in Fluorinated Tolanes on Their Photophysical Properties

by Masato Morita, Shigeyuki Yamada and Tsutomu Konno

Molecules 2021, 26(8), 2274; https://doi.org/10.3390/molecules26082274 - 14 Apr 2021

Cited by 18 | Viewed by 3019

Abstract

In this study, we synthesized a series of fluorinated and non-fluorinated tolanes, in which one or more fluorine atoms were systematically introduced into one aromatic ring of a tolane scaffold, and systematically evaluated their photophysical properties. All the tolanes with or without fluorine [...] Read more.

In this study, we synthesized a series of fluorinated and non-fluorinated tolanes, in which one or more fluorine atoms were systematically introduced into one aromatic ring of a tolane scaffold, and systematically evaluated their photophysical properties. All the tolanes with or without fluorine substituents were found to have poor photoluminescence (PL) in tetrahydrofuran (THF) solutions. On the other hand, in the crystalline state, non-fluorinated and fluorinated tolanes with one or four fluorine atoms were less emissive, whereas fluorinated tolanes with three or five fluorine atoms exhibited high PL efficiencies (Ф_PL) up to 0.51. X-ray crystallographic analyses of the emissive fluorinated tolanes revealed that the position of the fluorine substituent played a key role in achieving a high Ф_PL. Fluorine substituents at the ortho (2/6) and para (4) positions led to tight and rigid packing due to plural π–π stacking and/or hydrogen bonding interactions, resulting in enhanced Ф_PL caused by the suppression of non-radiative deactivation. Additionally, fluorinated tolanes with three fluorine atoms exhibited notable aggregation-induced PL emission enhancement in THF/water mixed solvents. This demonstrates that the PL characteristics of small PL materials can be tuned depending on the usage requirements. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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Review

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21 pages, 11914 KiB

Open AccessReview

Merging Electron Deficient Boronic Centers with Electron-Withdrawing Fluorine Substituents Results in Unique Properties of Fluorinated Phenylboronic Compounds

by Agnieszka Adamczyk-Woźniak and Andrzej Sporzyński

Molecules 2022, 27(11), 3427; https://doi.org/10.3390/molecules27113427 - 26 May 2022

Cited by 1 | Viewed by 2251

Abstract

Fluorinated boron species are a very important group of organoboron compounds used first of all as receptors of important bioanalytes, as well as biologically active substances, including Tavaborole as an antifungal drug. The presence of substituents containing fluorine atoms increases the acidity of [...] Read more.

Fluorinated boron species are a very important group of organoboron compounds used first of all as receptors of important bioanalytes, as well as biologically active substances, including Tavaborole as an antifungal drug. The presence of substituents containing fluorine atoms increases the acidity of boronic compounds, which is crucial from the point of view of their interactions with analytes or certain pathogen’s enzymes. The review discusses the electron acceptor properties of fluorinated boronic species using both the acidity constant (pK_a) and acceptor number (AN) in connection with their structural parameters. The NMR spectroscopic data are also presented, with particular emphasis on ¹⁹F resonance due to the wide range of information that can be obtained from this technique. Equilibria in solutions, such as the dehydration of boronic acid to form boroxines and their esterification or cyclization with the formation of 3-hydroxyl benzoxaboroles, are discussed. The results of the latest research on the biological activity of boronic compounds by experimental in vitro methods and theoretical calculations using docking studies are also discussed. Full article

(This article belongs to the Special Issue Organofluorine Chemistry and Beyond)

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