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

• materials in organic synthesis for the preparation of nitrogen-containing heterocycles. Moreover, biguanides demonstrate a wide range of biological activities and some representatives are worldwide known such as metformin, the first-line treatment against type II diabetes, or chlorhexidine, the gold

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

• glycerol α-chlorohydrin, the ratio of I/II was 1:4 with II being the preferred isomer but when using glycidol, this ratio shifted to 3:1 in the favor of the desired isomer [96][97]. From there on, the use of glycidol for the preparation of GNA analogues became the gold standard. The first GNA polymers were

• of NaHMDS in order to selectively alkylate the 2'-OH, followed by TBAF treatment to remove the MDPS protecting group. The 2'-O-MOE soon became the gold standard alkyl modification, owing to its improvement in therapeutically relevant properties. Compared to 2'-OMe RNA, the 2'-O-MOE RNA analogue has

Enhanced target cell specificity and uptake of lipid nanoparticles using RNA aptamers and peptides

• Roslyn M. Ray,
• Anders Højgaard Hansen,
• Maria Taskova,
• Bernhard Jandl,
• Jonas Hansen,
• Citra Soemardy,
• Kevin V. Morris and
• Kira Astakhova

Beilstein J. Org. Chem. 2021, 17, 891–907, doi:10.3762/bjoc.17.75

• , Denmark Institute of Biological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria School of Medical Sciences, Griffith University, Gold Coast, Australia 4222 Menzies Health Institute Queensland, Griffith University, Gold Coast, QLD 4222, Australia 10.3762/bjoc.17.75 Abstract

Synthesis, structural characterization, and optical properties of benzo[f]naphtho[2,3-b]phosphoindoles

• Mio Matsumura,
• Takahiro Teramoto,
• Masato Kawakubo,
• Masatoshi Kawahata,
• Yuki Murata,
• Kentaro Yamaguchi,
• Masanobu Uchiyama and
• Shuji Yasuike

Beilstein J. Org. Chem. 2021, 17, 671–677, doi:10.3762/bjoc.17.56

• . The reaction of 2 with borane in THF formed a borane complex 6 in 91% yield, and the reaction with chloro(dimethyl sulfide)gold afforded the gold complex 7 in 39% yield. The molecular structures of the synthesized phospholes 2−7 were confirmed by spectral analyses (1H, 13C, and 31P NMR as well as MS

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• -dimethoxyethane (Scheme 20) [60]. The difluorocarbene then added to cyclohexene (49) to form difluoronorcarane 50 with good yield. Under similar conditions tetramethylethylene afforded 1,1-difluorotetramethylcyclopropane (4). Trifluoromethyl derivatives of cadmium, bismuth, zinc, and gold: Bis(trifluoromethyl

• (Scheme 23) [64]. Fürstner et al. [67] showed that (trifluoromethyl)gold(I)triphenylphosphine in dichloromethane can be used for the production of difluorocyclopropanes at low temperatures. The advantage of the method is its stereoselectivity. The disadvantages include the stoichiometric use of gold, low

Selective synthesis of α-organylthio esters and α-organylthio ketones from β-keto esters and sodium S-organyl sulfurothioates under basic conditions

• Jean C. Kazmierczak,
• Roberta Cargnelutti,
• Thiago Barcellos,
• Claudio C. Silveira and
• Ricardo F. Schumacher

Beilstein J. Org. Chem. 2021, 17, 234–244, doi:10.3762/bjoc.17.24

• , and related compounds. Some of them are catalyzed by expensive transition metals, such as gold, iridium, palladium, and titanium. More recently, the selective formation of C–S bonds using 1,3-dicarbonyl compounds, followed by a C–C bond cleavage has emerged as a versatile and less expensive protocol

Au(III) complexes with tetradentate-cyclam-based ligands

• Ann Christin Reiersølmoen,
• Thomas N. Solvi and
• Anne Fiksdahl

Beilstein J. Org. Chem. 2021, 17, 186–192, doi:10.3762/bjoc.17.18

• ; cyclam derivatives; cyclopropanation; Introduction The importance of gold for humankind dates long back, and gold is linked to the evolution of many parts of the society. Contrary to the general fascination and importance of gold, the potential as homogenous catalyst has been neglected, compared to a

• range of other transition metals. The utilization of gold in synthetic organic chemistry has become a topic of interest during the last decades, as evidenced by the increasing number of review articles published in this period [1][2][3][4][5][6][7][8]. Whereas both gold(I) and gold(III) are proven to be

• catalytic active forms of gold, gold(I) has so far, received main attention, likely due to the higher stability, as demonstrated by the development of a high number of gold(I)-catalyzed transformations and ligated gold(I) complexes, along with improved mechanistic understanding [9][10][11][12][13][14][15

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• stereochemistry as catalysts [27]. The stereochemical properties were sensitive to the linker size and length, and the yield of the syn-head-to-tail-9,10:9',10'-cyclodimer could reach 97–98%. Traditional thiol-functionalized organic ligands decorated on the surface of gold nanoclusters (AuNCs) tend to generate a

• ] (“Cyclodextrin–gold nanocluster decorated TiO2 enhances photocatalytic decomposition of organic pollutants” by H. Zhu et al., J. Mater. Chem. A vol. 6, © 2017); permission conveyed through Copyright Clearing Center, Inc. Visible-light-driven conversion of benzyl alcohol to H2 and a vicinal diol or to H2 and

Supramolecular polymerization of sulfated dendritic peptide amphiphiles into multivalent L-selectin binders

• David Straßburger,
• Svenja Herziger,
• Katharina Huth,
• Moritz Urschbach,
• Rainer Haag and
• Pol Besenius

Beilstein J. Org. Chem. 2021, 17, 97–104, doi:10.3762/bjoc.17.10

• competitive surface plasmon resonance (SPR) binding assay, whereby neutral supramolecular polymers of I were used as control experiment. L-Selectin-coated gold nanoparticles were incubated with analyte solutions of different concentrations and subsequently probed on an SPR-chip modified with immobilized

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• Studi di Firenze, Via della Lastruccia 13, 50019 Sesto Fiorentino, Florence, Italy 10.3762/bjoc.16.255 Abstract The tandem gold(I)-catalyzed rearrangement/Nazarov reaction of enynyl acetates in which the double bond is embedded in a piperidine ring was computationally and experimentally studied. The

• substrates. Keywords: DFT calculations; gold catalysis; Nazarov reaction; N-heterocycles; Introduction In the development of new and effective catalysts, step economy is surely one of the major goals. A reduction of the number of steps in the synthesis of complex compounds can be attained by cascade

• reactions, which allow for structural modifications on the organic compounds by forming several chemical bonds in one pot. To this end, gold catalysis [1][2][3][4][5][6][7] has been widely exploited to construct various cyclic and heterocyclic frameworks through cascade reactions triggered by the activation

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• backbones in the presence of Ag2O provided exclusively the three homomeric cylinders [Ag3(13)2]3+, [Ag3(14)2]3+, and [Ag3(15)2]3+ (state: SelfSORT-I in Figure 7). Upon the addition of gold(I) ions, a one-pot transmetalation triggered an exchange of the Ag+ ions for Au+ in the tris-NHC ligand-based cylinders

Encrypting messages with artificial bacterial receptors

• Pragati Kishore Prasad,
• Naama Lahav-Mankovski,
• Leila Motiei and
• David Margulies

Beilstein J. Org. Chem. 2020, 16, 2749–2756, doi:10.3762/bjoc.16.225

• reversibly change the properties of the cell. For example, we have shown that synthetic receptors appended with a thiol or a folate group enable bacteria expressing the His-tagged outer membrane protein C (His-OmpC) to bind to gold surfaces or cancer cells, respectively [2]. We have also shown that this

Optical detection of di- and triphosphate anions with mixed monolayer-protected gold nanoparticles containing zinc(II)–dipicolylamine complexes

• Lena Reinke,
• Julia Bartl,
• Marcus Koch and
• Stefan Kubik

Beilstein J. Org. Chem. 2020, 16, 2687–2700, doi:10.3762/bjoc.16.219

• /bjoc.16.219 Abstract Gold nanoparticles covered with a mixture of ligands of which one type contains solubilizing triethylene glycol residues and the other peripheral zinc(II)–dipicolylamine (DPA) complexes allowed the optical detection of hydrogenphosphate, diphosphate, and triphosphate anions in

• preferred binding mode of zinc(II)–dipicolylamine complexes with phosphate anions which involves binding of the anion between two metal centers. This work thus provided information on how the behavior of mixed monolayer-protected gold nanoparticles is affected by multivalent interactions, at the same time

• introducing a method to assess whether certain biologically relevant anions are present in an aqueous solution within a specific concentration range. Keywords: chemosensor; diphosphate; gold nanoparticles; optical sensing; triphosphate; Introduction Gold nanoparticles (AuNPs) are versatile platforms for the

Water-soluble host–guest complexes between fullerenes and a sugar-functionalized tribenzotriquinacene assembling to microspheres

• Si-Yuan Liu,
• Xin-Rui Wang,
• Man-Ping Li,
• Wen-Rong Xu and
• Dietmar Kuck

Beilstein J. Org. Chem. 2020, 16, 2551–2561, doi:10.3762/bjoc.16.207

• 100 W ultrasonic cleaner. The surface morphology was investigated on a Phenom ProX scanning electron microscopy (SEM, Phenom World, Eindhoven, Netherlands). Samples were prepared from the freeze-dried aqueous solution/suspension of TBTQ-(OG)6, C60, and TBTQ-(OG)6 C60, and then gold-sputtered prior to

• , white: H for TBTQ-(OG)6; silver grey: C for C60). SEM images of (a) C60; (b) TBTQ-(OG)6; (c) and (d) TBTQ-(OG)6 C60 (C60: 1.4 mM; TBTQ-(OG)6: 1.4 mM in water, samples were freeze-dried and gold-sputtered before imaging). Synthetic route to TBTQ-(OG)6. Supporting Information Supporting Information File

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• they are the most trustworthy strategies for direct functionalization of aromatic scaffolds [50]. As can be inspected from Scheme 18, monoiodosumanene 79 was obtained by gold-catalyzed iodination in the presence of N-iodosuccinimide (NIS). The mononitrosumanene 80 was achieved through the nitration

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• photosensitized energy transfer: Photocatalysis, photochemical sensitization and photosensitization are very similar terms. The IUPAC gold book defines photosensitization as follows: “The process by which a photochemical or photophysical alteration occurs in one molecular entity as a result of the initial

Efficient [(NHC)Au(NTf₂)]-catalyzed hydrohydrazidation of terminal and internal alkynes

• Maximillian Heidrich and
• Herbert Plenio

Beilstein J. Org. Chem. 2020, 16, 2080–2086, doi:10.3762/bjoc.16.175

• alkynes (7a–j, 10 examples, 0.2–0.5 mol % [(NHC)Au(NTf2)], T = 60–80 °C) utilizing a complex with a sterically demanding bispentiptycenyl-substituted NHC ligand and the benign reaction solvent anisole, is reported. Keywords: alkyne; gold; homogeneous catalysis; hydrohydrazidation; NHC ligand

• ; Introduction Cationic gold complexes with weakly coordinating counterions (which are often considered to be solvent-separated ions) [1][2][3], render powerful catalysts for the transformation of organic substrates [4][5][6], specifically the reactions of alkynes with a variety of heteroatom nucleophiles

• (Scheme 1) [7] such as water or alcohol [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], primary or secondary amines [23][24][25][26][27][28], or hydrazine [29][30][31]. These reactions are synthetically useful since gold catalysis is characterized by a good functional group tolerance for

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• presumably renders an ionic [2 + 2] cycloaddition pathway competitive with the Diels–Alder reaction. The few reported examples of cyclobutene formation from alkynes and unactivated 1,3-dienes include the sensitized photocycloaddition of phenylacetylene and DMBD [30] and the gold(I)-catalyzed reaction of

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• oxidants and/or additives. In order to provide a solution towards these limitations of the undirected C–H activation, the group of Lee initiated a project merging gold-catalyzed C–H activation with photoredox catalysis (Figure 42) [104]. Such a dual catalytic system should promote the desired C–C bond

• -forming reaction under oxidant-free conditions, while the use of the gold catalyst gives promise of accessing highly site-selective transformations. Indeed, electrophilic Au(III) species were able to site-selectively activate C–H bonds of activated electron-rich arenes thus generating Au(III)–Ar species

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• which they detailed the Markovnikov hydrofluorination of alkynes using HF.DMPU coupled with a gold catalyst [60]. Accordingly, the appropriate propargylmalonate derivatives were fluorinated to give fluoroalkene intermediates, which were then converted into malonate-based enynes 37 (Z = CO2R) through a

Photoredox-catalyzed silyldifluoromethylation of silyl enol ethers

• Vyacheslav I. Supranovich,
• Vitalij V. Levin and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2020, 16, 1550–1553, doi:10.3762/bjoc.16.126

• )trimethylsilane followed by a reduction of the primary products with sodium borohydride is described. An 18 W, 375 nm LED was used as the light source. The reaction is performed in the presence of a gold photocatalyst, which effects the generation of a (trimethylsilyl)difluoromethyl radical via cleavage of the

• analyzed by 19F NMR spectroscopy. A series of typical photocatalysts (for example, iridium catalysts) were ineffective in promoting the reaction. Rewardingly, a gold catalyst, [AuCl(μ-dppm)]2 [25][26][27], provided reasonable yields of 3a after one day of irradiation along with a full conversion of the

• strongly reducing catalysts may be associated with the ability of gold to interact with the bromine atom of silane 1 followed by inner-sphere electron transfer [27]. The radical then attacks silyl enol ether 2, and the subsequent silyloxy-substituted radical is oxidized by the photocatalyst to generate the

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

• Alessandra Del Tito,
• Havall Othman Abdulla,
• Davide Ravelli,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

• alkyl radicals were easily accessed by the photocatalyzed reduction of the corresponding bromides, in turn promoting an efficient radical addition onto isonitriles. In one instance, the dimeric gold complex [Au2(dppm)2]Cl2 (dppm = bis(diphenylphosphino)methane) acted as the photocatalyst and activated

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

• Phil M. Pithan,
• Sören Steup and
• Heiko Ihmels

Beilstein J. Org. Chem. 2020, 16, 904–916, doi:10.3762/bjoc.16.82

• silver(I) or gold(III) ions, the spironaphthoxazine 1aSO or the corresponding 5-chloro-substituted analog underwent thermal–oxidative degradation even under an inert gas atmosphere in the dark [74][75]. Based on the formation of silver or gold nanoparticles during the reaction, the authors proposed a two

Regioselectively α- and β-alkynylated BODIPY dyes via gold(I)-catalyzed direct C–H functionalization and their photophysical properties

• Takahide Shimada,
• Shigeki Mori,
• Masatoshi Ishida and
• Hiroyuki Furuta

Beilstein J. Org. Chem. 2020, 16, 587–595, doi:10.3762/bjoc.16.53

• , Japan 10.3762/bjoc.16.53 Abstract A series of α- and β-ethynyl-substituted BODIPY derivatives (3a, 4a, 5a, 5b, 6a, 6b) were synthesized by gold(I)-catalyzed direct C–H alkynylation reactions of dipyrromethane and BODIPY, respectively, with ethynylbenziodoxolone (EBX) in a regioselective manner

• -materials. Keywords: alkynylation; BODIPY; direct C–H functionalization; gold(I); Introduction Boron-dipyrromethene (BODIPY, 1) and its derivatives are representative families of fluorophores that have been widely used in applications for bioimaging [1][2][3][4][5][6], photodynamic therapy [7][8][9][10

• BODIPY core has not yet been achieved. Inspired by the works of Waser and co-workers showing the gold(I)-catalyzed C–H electrophilic alkynylation of various heterocycles (e.g., pyrroles, indoles, etc.) with ethynylbenziodoxolone (EBX) as an activated ethynyl synthon [38][39][40][41][42], we investigated

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• thicker layers of Cu on Au nanoparticles. Other findings in this study were: a) copper leaching decreased using gold nanoparticles, b) increasing the dendron generation increased the diffusion resistance. As shown in Scheme 5, a silica nanomaterial was decorated with a novel copper complex of poly(N