Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• introduction of highly electronegative halides, such as fluorine or chlorine, on the phenyl ring afforded the substituted 9-methylanthracenes in lower yields. In addition, the method proposed by Lee and co-workers presented advantages that included shorter reaction times and milder reaction conditions [37

Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

• ]. Mimicking the natural cellulose synthases machinery can be foreseen to provide synthetic Cellulose I. Some enzymes offer the flexibility to produce modified cellulose structures. Cellulose oligomers with fluorine substitution at C-2, C-3 or C-6 position were prepared by cellodextrin phosphorylases [78

• , fluorine, and carboxymethyl groups, prevented the formation of insoluble aggregates by disrupting hydrogen-bond networks. Dramatic differences in the conformation (e.g., radius of gyration and glycosidic bond conformation) and aggregation behaviour (i.e., crystallinity and solubility) were observed for

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• to oxidize ethylbenzene without significant loss of activity and metal leaching. The authors have suggested a mechanism for the reaction involving radical species bearing a benzylic carbon–vanadium bond. Fluorine presents unique features and may lead to essential changes in the structural and

• also been reported for the direct C(sp3)–H fluorination. Chen and co-workers [94] described a fluorination method employing Selectfluor as fluorine source and the commercially available V2O3 to give fluorine-containing compounds under mild conditions and with moderate to good yields (Scheme 10B,C). The

• /hemiacetal avoiding undesirable elimination to the enamine, or attack at other electrophilic sites in complex substrates. The presence of a fluorine source like diethylaminosulfur trifluoride (DAST) or the Lewis acid boron trifluoride diethyl etherate (BF3·OEt2) result in the formation of reactive iminium or

Development of N-F fluorinating agents and their fluorinations: Historical perspective

• Teruo Umemoto,
• Yuhao Yang and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

• Teruo Umemoto Yuhao Yang Gerald B. Hammond Department Chemistry, University of Louisville, Lousiville, Kentucky 40292, USA 10.3762/bjoc.17.123 Abstract This review deals with the historical development of all N-F fluorinating agents developed so far. The unique properties of fluorine make

• salt; fluoropyridinium salt; fluorosulfonimide; Introduction Fluorinated organic compounds occupy an important position in pharmaceuticals [1], agrochemicals [2], and materials [3]. Especially, in the first two areas, the presence of fluorine has attracted attention during the last decades. Nowadays

• , a considerable number of medicines [4][5] and agrochemicals [6] contain at least one fluorine atom in their structures. The fluorine atom has unique properties such as the highest electronegativity, extremely low polarization, strong C–F bonds, and the smallest size after a hydrogen atom [7]. Thus

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• . Additionally, difluorination was observed with negligible amounts because the monofluorinated product is rendered more electronically deficient by the first fluorine atom. Based on an analysis by DFT calculations, the postulated reaction pathway of manganese-catalyzed C–H fluorination is described in Figure 1

• fluorine activation (see 22i–j), and the oxygen-containing natural terpenoid ambroxide was methylated at the methylene position next to the O atom on the tetrahydrofuran ring (see 22k). This manganese-catalyzed late-stage approach enables the direct methylation of unactivated C–H bonds with excellent site

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

• uracil with fluorine or trifluoromethyl improved PNA binding affinity for complementary DNA and RNA [127]. Moreover, fluorination increased the cellular uptake of PNAs [127]. Fluorinated uracil derivatives are also useful probes for studying different binding modes of PNA using 19F NMR [128]. PNA

2,4-Bis(arylethynyl)-9-chloro-5,6,7,8-tetrahydroacridines: synthesis and photophysical properties

• Najeh Tka,
• Mohamed Adnene Hadj Ayed,
• Mourad Ben Braiek,
• Mahjoub Jabli,
• Noureddine Chaaben,
• Kamel Alimi,
• Stefan Jopp and
• Peter Langer

Beilstein J. Org. Chem. 2021, 17, 1629–1640, doi:10.3762/bjoc.17.115

• profile with two transitions located at 386 and 400 nm. Methyl-substituted derivative 4b gave a slight red shift of 10 nm as compared to 4a. In contrast, fluorine and trifluoromethyl-substituted derivatives 4e and 4f show nearly the same emission. However, derivative 4g containing an electron-donating

• . Due to their low donating effect, the methyl group in product 4b induce an addition of yellow regions into the external phenyl rings. However, the electron-deficient fluorine atom in derivative 4e results in a decrease of the electron density of the tetrahydroacridine core and the external phenyl

• ground state from the optimized chemical structure of obtained molecules (Table 5). The calculated permanent dipole moments µ (D) have considerably increased values for 4f and 4g, which show significant changes in their experimental emission properties. The presence of six fluorine atoms induces a large

Recent advances in the application of isoindigo derivatives in materials chemistry

• Andrei V. Bogdanov and
• Vladimir F. Mironov

Beilstein J. Org. Chem. 2021, 17, 1533–1564, doi:10.3762/bjoc.17.111

• significant effect of the structure of the substituent at the nitrogen atom of the heterocycle on the OSC efficiency was also shown [29][30]. Thus, fluorine-substituted polymers 18a,b in the composition with PC61BM showed a PCE of only 0.9–1.4%, while an OSC based on ethoxylated derivative 19a was

• ][32][33]. In the course of further studies, the key influence of the nature of both the substituent at the nitrogen atom of isoindigo and at the bithiophene moiety on the OSC efficiency was confirmed. Thus, the introduction of fluorine atoms to thiophene rings in compound 22b leads to an increase in

• the above described study, Liu et al. demonstrated that this type of compounds is promising by means of introducing fluorine atoms into the thiophene ring [43]. The use of compound 29c (ratio of monomer units n/m = 2:1) as an acceptor component of the OSC made it possible to achieve one of the highest

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• fluorine-containing organic molecules combined with the 1,4-quinone moiety can be considered as a challenging problem of current organic synthesis. Thus, the main goal of the present study was to check the course of [3 + 2]-cycloaddition reactions of electron-deficient CF3-substituted nitrile imines 7 with

Iodine-catalyzed electrophilic substitution of indoles: Synthesis of (un)symmetrical diindolylmethanes with a quaternary carbon center

• Thanigaimalai Pillaiyar,
• Masoud Sedaghati,
• Andhika B. Mahardhika,
• Lukas L. Wendt and
• Christa E. Müller

Beilstein J. Org. Chem. 2021, 17, 1464–1475, doi:10.3762/bjoc.17.102

• -fluorinated analogs [25]. Considering the ever-growing demand for organofluorine compounds, the development of new methodologies that allow the incorporation of fluorine atoms into bioactive molecules is highly desired and will also be addressed herein. Recently, the use of indol-3-ylmethanols as

Structural effects of meso-halogenation on porphyrins

• Keith J. Flanagan,
• Maximilian Paradiz Dominguez,
• Zoi Melissari,
• Hans-Georg Eckhardt,
• René M. Williams,
• Dáire Gibbons,
• Caroline Prior,
• Gemma M. Locke,
• Alina Meindl,
• Aoife A. Ryan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2021, 17, 1149–1170, doi:10.3762/bjoc.17.88

• that the fluorine atom is too small to overly impact the overall packing. This structure has a planar conformation similar to that of 2,3,7,8,12,13,17,18-octaethylporphyrin [41]. Due to the high disorder in the crystal structure (the fluorine atom is disordered over the four meso positions) an accurate

• accounting of the interaction profile is not possible. However, there is the appearance of an F···H interaction between the ethyl groups and the fluorine atom which is projected throughout the crystal packing (Supporting Information File 1, Figure S57). In compounds 21 and 22, the number of β-halogen atoms

• mono- and di-halo-substituted porphyrins are only marginally different. The difference between the meso-free and fluorine derivatives is minimal. For the chloro to iodo derivatives, the disubstitution only exhibits a marginal decrease in the out-of-plane distortion relative to the mono-substitution

Synthesis of multiply fluorinated N-acetyl-D-glucosamine and D-galactosamine analogs via the corresponding deoxyfluorinated glucosazide and galactosazide phenyl thioglycosides

• Vojtěch Hamala,
• Lucie Červenková Šťastná,
• Martin Kurfiřt,
• Petra Cuřínová,
• Martin Dračínský and
• Jindřich Karban

Beilstein J. Org. Chem. 2021, 17, 1086–1095, doi:10.3762/bjoc.17.85

• enzymes [1][2][3][4][5][6][7]. The introduction of additional fluorine atoms into a monofluorinated carbohydrate is an attractive way of modulating the binding affinity and pharmacokinetic properties of fluorinated glycomimetics. Hydrophobic segments incorporating multiple C–F bonds could (1) reduce the

• biomedical applications due to their ability to inhibit the glycan and glycosaminoglycan biosynthesis [34][35][36][37]. The fluorine substituent has typically been introduced into these GlcNAc and GalNAc analogues using nucleophilic fluorination. The primary position (C6 hydroxy group) was fluorinated by

• DAST [22][25][26][30][35], or reaction of C3/C4 methanesulfonate or trifluoromethanesulfonate esters with a source of nucleophilic fluorine, such as TBAF or KF [22][25][34]. Although these fluorinations usually proceeded with inversion of configuration, the acetylated 3-fluoro-GlcNAc analogue was most

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• ]. Longer reaction times and lower temperatures were used to improve the first step that resulted in very good yields. Recently, Xiao et al. used this method for the synthesis of 13 new fluorine-containing proguanil derivatives which were found to be more active than proguanil in five human cancerous cell

Beyond ribose and phosphate: Selected nucleic acid modifications for structure–function investigations and therapeutic applications

• Christopher Liczner,
• Kieran Duke,
• Gabrielle Juneau,
• Martin Egli and
• Christopher J. Wilds

Beilstein J. Org. Chem. 2021, 17, 908–931, doi:10.3762/bjoc.17.76

• acids (ANA) are analogs of RNA where the hydroxy group at C2' is inverted (Figure 1G). In fluoroarabino nucleic acids (FANA) this C2' hydroxy group is replaced by fluorine. Arabino- and fluoroarabino nucleosides have demonstrated anticancer and antiviral activities (as reviewed in [173]). β-ᴅ

• , the natural DNA sequence had a half-life of 1 min [202]. The incorporation of fluorine at the C4' position has long constituted a challenge owing to the instability of the glycosidic bond in the resulting nucleosides. This modification is desirable due to its involvement in the mode of action of the

• natural antibiotic nucleocidin [203][205]. Damha reasoned that the incorporation of fluorine at both C2' and C4' could lead to a stable nucleoside due to the glycosidic bond stabilization brought about by 2'-fluorination [206] which turned out to be correct after successful isolation of both 2',4'-diF-rU

Manganese/bipyridine-catalyzed non-directed C(sp³)–H bromination using NBS and TMSN₃

• Kumar Sneh,
• Takeru Torigoe and
• Yoichiro Kuninobu

Beilstein J. Org. Chem. 2021, 17, 885–890, doi:10.3762/bjoc.17.74

• gram scale. The introduced bromine atom can be converted into fluorine and allyl groups. Keywords: bromination; C–H transformation; hydrogen abstraction; manganese; radical; Introduction Organic halides are versatile precursors for various synthetic protocols and are frequently used to introduce a

• reaction proceeded regioselectively at the methine C(sp3)–H bond of isoamyl benzoate (1b) to give 2b in 64% yield. Isoamyl benzoates bearing halogen atoms, such as fluorine, chlorine, or bromine, on the phenyl ring were also suitable substrates and gave C(sp3)–H brominated products 2c–e in 49–60% yields

• functionalized upon the introduction of other functional groups, such as fluorine and allyl groups. We hope that this C(sp3)–H bromination reaction will become a useful method to synthesize organic compounds with bromine atom(s). Several examples of C(sp3)–H halogenation. Substrate scope. a80 °C. b45 min. c4 h

Organo-fluorine chemistry V

• David O’Hagan

Beilstein J. Org. Chem. 2021, 17, 737–738, doi:10.3762/bjoc.17.63

• David O'Hagan School of Chemistry, Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, United Kingdom 10.3762/bjoc.17.63 Keywords: Organo-fluorine chemistry; This is the fifth thematic issue on organo-fluorine chemistry in the Beilstein Journal

• Beilstein Journal of Organic Chemistry has become a settled home for papers in contemporary organo-fluorine chemistry. Authors have presented their recent findings or, in some cases, reviewed important areas, from bioactives to materials, and collectively the papers highlight the vibrancy and range of

• activity associated with this theme. Organo-fluorine chemistry merits our attention as an important discipline within contemporary organic chemistry contributing in a unique way to innovation and performance in the development of functional molecules. This issue will be historically memorable as all of the

Metal-free visible-light-enabled vicinal trifluoromethyl dithiolation of unactivated alkenes

• Xiaojuan Li,
• Qiang Zhang,
• Weigang Zhang,
• Jinzhu Ma,
• Yi Wang and
• Yi Pan

Beilstein J. Org. Chem. 2021, 17, 551–557, doi:10.3762/bjoc.17.49

• . Keywords: alkenes; difunctionalization; metal-free; photoredox; trifluoromethylthiolation; Introduction The incorporation of fluorine atoms into drug molecules will significantly enhance the physical, chemical, and biological properties of the pharmaceuticals [1][2][3][4][5][6]. Modifying drug candidates

• by introducing fluorine-containing (such as -CF3, -CF2H, -C2F5, -SCF3, -OCF3) moieties has become a substantial strategy for medicinal research [2][7][8]. Among the fluorinated functionalities, the trifluoromethylthio group (SCF3) has strong electron-withdrawing properties and a higher lipophilicity

Synthesis and physicochemical evaluation of fluorinated lipopeptide precursors of ligands for microbubble targeting

• Masayori Hagimori,
• Estefanía E. Mendoza-Ortega and
• Marie Pierre Krafft

Beilstein J. Org. Chem. 2021, 17, 511–518, doi:10.3762/bjoc.17.45

• -surfactants to the phospholipid molecules of the MB shell and strongly reduce its interfacial tension [35][36]. Recent studies have reported that the fluorine–fluorine interactions that develop between the FC and the MB shell component (e.g., fluorinated biomarkers [37] and fluorinated nanoparticles

• fluorine–fluorine interactions. Experimental Materials. We purchased Fmoc-protected amino acids, N,N-dimethylformamide (DMF), dichloromethane (DCM), methanol, 1-hydroxybenzotriazole (HOBT), 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU), N,N-diisopropylethylamine (DIPEA

Synthesis of N-perfluoroalkyl-3,4-disubstituted pyrroles by rhodium-catalyzed transannulation of N-fluoroalkyl-1,2,3-triazoles with terminal alkynes

• Olga Bakhanovich,
• Viktor Khutorianskyi,
• Vladimir Motornov and
• Petr Beier

Beilstein J. Org. Chem. 2021, 17, 504–510, doi:10.3762/bjoc.17.44

• ][22], and pyrroles [19]. The use of fluorine atoms and fluoro groups (including the trifluoromethyl group) is a widely used strategy to improve the properties of drug candidates or agrochemicals [23][24][25][26][27][28]. The development of new methods for the synthesis of selectively fluorinated and

Biochemistry of fluoroprolines: the prospect of making fluorine a bioelement

• Vladimir Kubyshkin,
• Rebecca Davis and
• Nediljko Budisa

Beilstein J. Org. Chem. 2021, 17, 439–460, doi:10.3762/bjoc.17.40

• proline-to-fluoroproline substitutions could be possible. We suggest a hypothetical scenario for the use of laboratory evolutionary methods with fluoroprolines as a suitable vehicle to introduce fluorine into living cells. This approach may enable creation of synthetic cells endowed with artificial

• biodiversity, containing fluorine as a bioelement. Keywords: amino acids; evolution; fluorine; proline; proteins; Introduction Nature employs a rather small set of chemical elements for constructing the core biochemical makeup. Most elements of the periodic table are excluded from the biochemical world. Not

• surprisingly, researches have been intrigued by an idea to introduce certain elements into biochemical schemes artificially. Of the many possible elements to introduce, fluorine is arguably the most suited for being used as an artificial bioelement [1]. Organofluorine chemistry is very diverse, and many

Synthesis of trifluoromethyl ketones by nucleophilic trifluoromethylation of esters under a fluoroform/KHMDS/triglyme system

• Yamato Fujihira,
• Yumeng Liang,
• Makoto Ono,
• Kazuki Hirano,
• Takumi Kagawa and
• Norio Shibata

Beilstein J. Org. Chem. 2021, 17, 431–438, doi:10.3762/bjoc.17.39

• , Nagoya 466-5888, Japan Tosoh Finechem Corporation, 4988, Kaiseicho, Shunan, 746-0006, Japan Institute of Advanced Fluorine-Containing Materials, Zhejiang Normal University, 688 Yingbin Avenue, 321004 Jinhua, China 10.3762/bjoc.17.39 Abstract A straightforward method that enables the formation of

• of fluorine(s) into organic molecules usually leads to significant changes in the chemical and physicochemical properties of the original compounds [5][6]. Hence, the fluorination and related fluoro-functionalization of drug candidates are powerful strategies in drug design to appropriately bias

• examined [46]. Trifluoromethyl ketones (TFMKs) are valuable fluorine-containing synthetic targets of bioactive compounds [55][56] that behave as mimics of the tetrahedral transition-state intermediate of enzymatic hydrolysis of esters and amides by stabilizing their hydrates (Figure 1a) [57]. In fact, the

Unexpected rearrangements and a novel synthesis of 1,1-dichloro-1-alkenones from 1,1,1-trifluoroalkanones with aluminium trichloride

• Beatrice Lansbergen,
• Catherine S. Meister and
• Michael C. McLeod

Beilstein J. Org. Chem. 2021, 17, 404–409, doi:10.3762/bjoc.17.36

• 5m compared to the longer chain substrates (e.g., 5c and 5l) could be explained mechanistically by the formation of a terminal carbocation upon the extraction of a fluorine atom by the aluminium species (Scheme 3). This carbocation could be stabilised to varying degrees by the ketone moiety

Helicene synthesis by Brønsted acid-catalyzed cycloaromatization in HFIP [(CF₃)₂CHOH]

• Takeshi Fujita,
• Noriaki Shoji,
• Nao Yoshikawa and
• Junji Ichikawa

Beilstein J. Org. Chem. 2021, 17, 396–403, doi:10.3762/bjoc.17.35

• fluorine, which helps to generate cations but does not affect cationic reactions [23][24][25][26][27]. Thus, HFIP greatly facilitates reactions via cationic intermediates [28]. In the presence of a catalytic amount of trifluoromethanesulfonic acid in HFIP, (biaryl-2-yl)acetoaldehydes or their acetal

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• cations is probably the α-(trifluoromethyl) carbocation. Many efforts are currently devoted to develop methods allowing the efficient insertion of fluorine atoms or fluorinated groups into organic molecules [7][8][9][10][11][12]. The increasing demand for fluorinated scaffolds, due to the striking

• beneficial effects generally resulting from the introduction of these fluorinated motifs [13], also participated in this development. These fluorine effects are nowadays remarkably established in many domains, including medicinal, organic, and organometallic chemistry, catalysis, chemical biology, and

• optimization of the geometry for CF3CH2+ at the STO-3G level led to an energy minimum, in which one of the fluorine atoms is significantly closer to the positive carbon center (Figure 1, top, θ = 101°) [24]. However, exactly the same structural distortion was calculated for the ethyl cation. Furthermore, the

¹⁹F NMR as a tool in chemical biology

• Diana Gimenez,
• Aoife Phelan,
• Cormac D. Murphy and
• Steven L. Cobb

Beilstein J. Org. Chem. 2021, 17, 293–318, doi:10.3762/bjoc.17.28

• use of 19F NMR in the broad field of chemical biology [Cobb, S. L.; Murphy, C. D. J. Fluorine Chem. 2009, 130, 132–140] and present here a summary of the literature from the last decade that has the technique as the central method of analysis. The topics covered include the synthesis of new

• biosynthesis and biodegradation of fluorinated organic compounds is also described. Keywords: biotransformation; chemical biology; fluorine; 19F NMR; probes; protein structure; Introduction Although fluorine is abundant in the environment, it is not a nutrient nor is it a feature of biochemistry for most

• ]. Furthermore, owing to the lack of naturally-occurring fluorinated compounds, fluorine is a useful probe to investigate structure and mechanism of biological molecules. Central to these studies is fluorine-19 nuclear magnetic resonance spectroscopy (19F NMR), which allows the user to readily visualize changes