pH- and concentration-dependent supramolecular self-assembly of a naturally occurring octapeptide

• Goutam Ghosh and
• Gustavo Fernández

Beilstein J. Org. Chem. 2020, 16, 2017–2025, doi:10.3762/bjoc.16.168

• the desired pH values. AFM samples were prepared by drop-casting 10 μL of the respective sample onto a mica surface, followed by spin-coating at 1000 rpm, and then, the thin film was dried at room temperature for 24 h. After that, images were captured on a Multimode® 8 SPM System (AXS Bruker). Silicon

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

• high diastereoselectivity [56]. In contrast to previous silicon-based tethers, which reacted in low yields and resulted in unexpected byproducts, this transformation could be performed on a multigram scale and showed a wide substrate scope and functional group compatibility, as well as high

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

• carbon–bromine bond. Keywords: difluoroalkylation; organofluorine compounds; photocatalysis; radical addition; silicon reagents; Findings Fluorinated silicon reagents have found widespread use for the introduction of fluorinated fragments [1][2][3][4][5]. Typically, these reagents work under strongly

• product with concomitant production of TMSBr. Conclusion In summary, a method for the introduction of the silyldifluoromethyl group was described by the coupling of a readily available silicon reagent with silyl enol ethers. The reaction is promoted by light and involves the generation of a fluorinated

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• material is drastically different for inorganic and organic semiconductors. High εr(ω) materials, such as silicon (εr(ω) = 12) or GaAs (εr(ω) = 13), effectively screen the Coulombic attraction between excitons to 10s of meV, allowing the charge carriers to easily dissociate at room temperature [109][110

• imitate light transmission through flesh, as this is relevant for photocatalyst applications in photodynamic therapy [197][198][199]. They reported that the NIR photons penetrated 293 times deeper into the polymerisation medium and enabled the reaction to be applicable on a multigram scale through silicon

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• underwent a thermal rearrangement to generate tricyclic isobenzofurans 313 through the ring-cleavage of the thietanes. It was assumed that the rearrangement was assisted through participation of the oxygen lone-pair electrons [17] (Scheme 57). The silicon-containing phenyl triphenylsilyl thioketone (316

The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts

• Svetlana A. Kuznetsova,
• Alexander S. Gak,
• Yulia V. Nelyubina,
• Vladimir A. Larionov,
• Han Li,
• Michael North,
• Vladimir P. Zhereb,
• Alexander F. Smol'yakov,
• Artem O. Dmitrienko,
• Michael G. Medvedev,
• Igor S. Gerasimov,
• Ashot S. Saghyan and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2020, 16, 1124–1134, doi:10.3762/bjoc.16.99

• F-1a phase) that were immediately put into silicon grease and cooled to 120 K at the diffractometer. The data collection revealed a triclinic P-1 phase, with the lattice parameters a = 13.416(7) Å, b = 13.887(7) Å, c = 22.730(12) Å, α = 88.564(8)°, β = 87.351(8)°, γ = 89.836(9)°, cell volume = 4229

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• incorporating silicon or boron into new or existing drugs, in addition to their use as building blocks in cross-coupling reactions en route to various targets of both natural and unnatural origins. In this review, recent protocols relying on copper-catalyzed sp3 carbon–silicon and carbon–boron bond-forming

• functional groups into existing or new drugs. Examples include the incorporation of silicon bioisosteres that help increase lipophilicity, subsequently altering the existing metabolic pathway of a drug due to differences in its physicochemical properties [8]. On the other hand, the trigonal planar nature of

• boron can lead to dative bond formation with enzymes, and therefore increase binding affinity. As shown in Scheme 1, several silicon [9][10][11][12] and boron-containing [13][14][15][16] drugs have already entered the market, or are currently in the drug development pipeline. As the number of drugs

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

• : triisopropylsilyl group; Mes: 2,4,6-trimethylphenyl group. Top and front views of the crystal structures of (a) 4a and (b) 6b with 50% thermal ellipsoid probabilities. The isopropyl groups on the silicon atom are omitted in the front view for clarity. Partial 1H NMR spectra of (a) 1a, (b) 3a, (c) 4a, (d) 5a, and (e

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

• applications that focused on the title catalysts in CuAAC reactions. Review Copper anchored on functionalized silica materials: efficient and recyclable catalysts for CuAAC reactions In recent years, silica or silicon dioxide nanomaterials have received much attention from researchers and industry and have

• been used in a wide spectrum of applications. Silica nanomaterials have the empirical formula SiO2 in which one silicon atom covalently links to four oxygen atoms, and most of the oxygen bond to two silicon atoms. Hence, their atoms are randomly oriented to produce amorphous structures. These materials

Copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters with chiral phenol–carbene ligands

• Shohei Mimura,
• Sho Mizushima,
• Yohei Shimizu and
• Masaya Sawamura

Beilstein J. Org. Chem. 2020, 16, 537–543, doi:10.3762/bjoc.16.50

• compounds was examined. Because the separation of the product from silicon-based byproducts was troublesome, the isolated yields were lower than the yields determined by NMR spectroscopy (2a, 52%, Table 2, entry 1). When (E)-1a was used as the substrate, the opposite enantiomer (S)-2a was obtained in >99

• magnetic stirring bar. The vial was sealed with a teflon-coated silicon rubber septum. N,N-Dimethylacetamide (0.90 mL) was added to the vial, and then the mixture was stirred at room temperature for 5 min. Next, t-AmOH (16.3 μL, 0.15 mmol) was added, and the vial was taken out of the glove box. To the

Allylic cross-coupling using aromatic aldehydes as α-alkoxyalkyl anions

• Akihiro Yuasa,
• Kazunori Nagao and
• Hirohisa Ohmiya

Beilstein J. Org. Chem. 2020, 16, 185–189, doi:10.3762/bjoc.16.21

• stirring bar. The vial was sealed with a Teflon®-coated silicon rubber septum, and then the vial was evacuated and filled with nitrogen. Toluene (0.6 mL) was added to the vial, and then the mixture was stirred at 25 °C for 10 min. Next, PhMe2SiB(pin) (104.9 mg, 0.4 mmol) and benzaldehyde (1a, 42.4 mg, 0.4

• mmol) were added, and the mixture (mixture A) was stirred at 25 °C for 10 min. Meanwhile, Pd(OCOCF3)2 (2.0 mg, 0.006 mmol) and DPPF (3.3 mg, 0.006 mmol) were placed in another vial. This vial was sealed with a Teflon®-coated silicon rubber septum and then evacuated and filled with nitrogen. After

Efficient method for propargylation of aldehydes promoted by allenylboron compounds under microwave irradiation

• Jucleiton J. R. Freitas,
• Queila P. S. B. Freitas,
• Silvia R. C. P. Andrade,
• Juliano C. R. Freitas,
• Roberta A. Oliveira and
• Paulo H. Menezes

Beilstein J. Org. Chem. 2020, 16, 168–174, doi:10.3762/bjoc.16.19

• organometallic species of Cd [16], Ga [17], In [18], Ti [19], Al [20] and Bi [21] were described. However, the majority of these methods involve reagents that are difficult to prepare and to handle due to the sensitivity to air and moisture. The use of less reactive species based on tin [22][23][24], silicon [25

A new approach to silicon rhodamines by Suzuki–Miyaura coupling – scope and limitations

• Thines Kanagasundaram,
• Antje Timmermann,
• Carsten S. Kramer and
• Klaus Kopka

Beilstein J. Org. Chem. 2019, 15, 2569–2576, doi:10.3762/bjoc.15.250

• Cancer Consortium (DKTK), Heidelberg, Germany 10.3762/bjoc.15.250 Abstract Background: Silicon rhodamines are of particular interest because of their advantageous dye properties (fluorescence- and biostability, quantum efficiency, tolerance to photobleaching). Therefore, silicon rhodamines find frequent

• gave access to silicon rhodamines in poor to moderate yields, we wanted to improve these first valuable experimental results. Results: The preparation of the xanthene triflate was enhanced and several boron sources were screened to find the optimal coupling partner. After optimization of the palladium

• catalyst, different substituted boroxines were assessed to explore the scope of the Pd-catalyzed cross-coupling reaction. Conclusions: A number of silicon rhodamines were synthesized under the optimized conditions in up to 91% yield without the necessity of HPLC purification. Moreover, silicon rhodamines

Probing of local polarity in poly(methyl methacrylate) with the charge transfer transition in Nile red

• Aydan Yadigarli,
• Qimeng Song,
• Sergey I. Druzhinin and
• Holger Schönherr

Beilstein J. Org. Chem. 2019, 15, 2552–2562, doi:10.3762/bjoc.15.248

• solvents were checked for the lack of fluorescence when excited with 450–600 nm. Polymer films with or without NR were prepared by spin-casting of 3 wt % polymer solutions in 1,2-dichloroethane, dichloromethane or chloroform on silicon wafers (for ellipsometry) and on 20 × 20 × 0.15 mm3 Metzler glass

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• phosphine with poly(methylhydrosiloxane) in the presence of titanium(IV) isopropoxide (Scheme 4). The work-up of the reaction mixture with 25% HF allowed to remove silicon and titanium impurities and purification of 23 by column chromatography on silica gel yielded the product in 62%. 4

Synthesis of a dihalogenated pyridinyl silicon rhodamine for mitochondrial imaging by a halogen dance rearrangement

• Jessica Matthias,
• Thines Kanagasundaram,
• Klaus Kopka and
• Carsten S. Kramer

Beilstein J. Org. Chem. 2019, 15, 2333–2343, doi:10.3762/bjoc.15.226

• .15.226 Abstract Background: Since their first synthesis, silicon xanthenes and the subsequently developed silicon rhodamines (SiR) gained a lot of attention as attractive fluorescence dyes offering a broad field of application. We aimed for the synthesis of a fluorinable pyridinyl silicon rhodamine for

• ; mitochondrial probe; near-infrared (NIR) dyes; one-pot reaction; silicon rhodamines; Introduction Since their first synthesis by Fu and co-workers in 2008 [1], silicon xanthenes and the subsequently developed silicon rhodamines (SiR) have drawn a lot of attention as attractive fluorescence dyes offering a

• features with their optical properties and control the latter by rational dye design [15][24][25][26]. These investigations led to new silicon rhodamine dyes with enhanced and fine-tuned properties (quantum yield, lifetime, brightness, absorption and emission maxima). A recent review compared the

Halide metathesis in overdrive: mechanochemical synthesis of a heterometallic group 1 allyl complex

• Ross F. Koby,
• Nicholas R. Rightmire,
• Nathan D. Schley,
• Timothy P. Hanusa and
• William W. Brennessel

Beilstein J. Org. Chem. 2019, 15, 1856–1863, doi:10.3762/bjoc.15.181

• distance of K+ to Me3SiH, chosen to represent somewhat more accurately the type of interactions occurring in [KCsA'2], is slightly shorter (3.14 Å) and stronger (30 kJ mol–1), probably a result of the lower electronegativity of silicon compared to carbon and the correspondingly more negative methyl groups

The cyclopropylcarbinyl route to γ-silyl carbocations

• Xavier Creary

Beilstein J. Org. Chem. 2019, 15, 1769–1780, doi:10.3762/bjoc.15.170

• ; rearrangement; silicon; Introduction Carbocations, positively charged trivalent carbon compounds and reactive intermediates, have continued to fascinate chemists since the early discoveries of tropylium [1][2] and trityl [3][4][5][6][7] salts. Many of the giants of organic chemistry during the last century

• incorporated into this paper is the trimethylsilyl-substituted carbocation [36][37][38][39][40][41][42][43][44]. We have been interested in long-range interactions of silicon with both carbene [45][46][47][48] and carbocation centers [49][50]. Along these lines, γ-trimethylsilyl cations of general type 11 have

• of the cation. These features suggest more facile nucleophilic attack should occur at silicon, favoring bicyclobutane formation. Also included in Table 3 are calculated bond lengths in the phosphoryl-substituted cation 74d, which also shows a very long Si–C bond. Preferred trimethylsilyl elimination

Functional panchromatic BODIPY dyes with near-infrared absorption: design, synthesis, characterization and use in dye-sensitized solar cells

• Quentin Huaulmé,
• Cyril Aumaitre,
• Outi Vilhelmiina Kontkanen,
• David Beljonne,
• Alexandra Sutter,
• Gilles Ulrich,
• Renaud Demadrille and
• Nicolas Leclerc

Beilstein J. Org. Chem. 2019, 15, 1758–1768, doi:10.3762/bjoc.15.169

• , a set of DSSCs were fabricated following a procedure reported previously [4]. The J(V) characteristics of the devices were recorded in dark and upon irradiation with a mask. For the measurements a solar simulator with AM 1.5G filter was used after calibration with a Silicon cell at 1000 W m−2. For a

Selenophene-containing heterotriacenes by a C–Se coupling/cyclization reaction

• Pierre-Olivier Schwartz,
• Sebastian Förtsch,
• Astrid Vogt,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2019, 15, 1379–1393, doi:10.3762/bjoc.15.138

• parent system, diselenolo[3,2-b:2’,3’-d]selenophene (DSS), is still unknown. Cheng et al. published a synthesis of various heterotriacenes including two selenophenes bridged with other elements such as silicon, germanium, nitrogen, and carbon [26]. Very recently, Wang et al. released selenophene-based

Synthesis of polydicyclopentadiene using the Cp₂TiCl₂/Et₂AlCl catalytic system and thin-layer oxidation of the polymer in air

• Zhargolma B. Bazarova,
• Ludmila S. Soroka,
• Alex A. Lyapkov,
• Мekhman S. Yusubov and
• Francis Verpoort

Beilstein J. Org. Chem. 2019, 15, 733–745, doi:10.3762/bjoc.15.69

• by a spectrophotometer Thermo Scientific Evolution 201 using a wavelength range from 200 to 900 nm. Infrared spectra of the polymer were registered applying an FTIR spectrometer Simeks FT-801 in the range from 500 to 4000 cm−1. A silicon plate with a diameter of 8 mm was applied to support the

• (thin layer on silicon) with respect to intensities of adsorption bands at 1410 and 700 cm−1. The distribution of oxygen concentration in the polymer layer: 1 – a layer of oxidized cross-linked polymer; 2 – a layer of non-oxidized polymer. Dependence of the ratio of adsorption bands at 1700 and 700 cm−1

• on the exposure time of the layer in air at ambient temperature. Infrared spectra (a) of products of cationic polymerization of DCPD, stabilized with an antioxidant, after 24 hours (curve 1) and 1030 hours (curve 2) after synthesis (thin layer on silicon wafer) and (b) the correlation of intensity

Synthesis of C₃-symmetric star-shaped molecules containing α-amino acids and dipeptides via Negishi coupling as a key step

• Sambasivarao Kotha and
• Saidulu Todeti

Beilstein J. Org. Chem. 2019, 15, 371–377, doi:10.3762/bjoc.15.33

• treated with silicon tetrachloride and ethanol (SiCl4/EtOH) at room temperature for 6 h to produce the iodonated trimerized product 9 in 71% yield (Scheme 2) [45][46]. Then, the organozinc reagent 7 was coupled with triiodo derivative 9 in the presence of tetrakis(triphenylphosphane)palladium(0) (Pd(PPh3

Application of olefin metathesis in the synthesis of functionalized polyhedral oligomeric silsesquioxanes (POSS) and POSS-containing polymeric materials

• Patrycja Żak and
• Cezary Pietraszuk

Beilstein J. Org. Chem. 2019, 15, 310–332, doi:10.3762/bjoc.15.28

• the properties and applications of the resulting materials. Vinylsilanes show a specific reactivity towards alkylidene ruthenium complexes because of a strong effect of the silyl group on the properties of the double bond. In general, the substituents at the silicon atom determine the regioselectivity

• of the process to a certain degree. The reactivity of vinylsilanes with different substituents at silicon towards alkylidene ruthenium complexes is illustrated in Scheme 1 [7]. According to Scheme 1a, as a result of the reaction of trialkoxy-, tris(trimethylsiloxy)-, trichloro- or dichloromethyl

• mild conditions, hydrogenolysis of the benzyl ester group to the carboxylic acid and hydrogenation of the C=C double bonds at the silicon atoms (Scheme 7). The ability of the obtained derivatives, in particular the carboxylic acids, to generate nanostructured materials through self-organization

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• phenyl groups at the silicon atom are converted by acids (e.g., TFA or TfOH) and following aqueous work-up into silanediols [2][4][7][8][9][10][11]. Another route employs dichlorosilanes, which hydrolyze directly with nucleophiles (e.g., water [12][13][14][15][16][17] or hydroxide [18][19][20][21][22

• Nucleophilic substitution at silicon is already discussed with SN2 mechanism, following a backside attack opposite of the leaving group, as well as a front side attack near the leaving group [62][63][64][65][66][67][68]. A backside attack at the silicon in dichlorosilane 7 and monochlorosilanol 8 is blocked by

• the backbone, making a consideration of the mechanism not necessary. A mechanism with a pentacoordination at the silicon is assumed for the hydrolyses of BIFOXSiCl2 (7) to BIFOXSiCl(OH) (8) as intermediate and BIFOXSI(OH)2 (9) as product [65][66][67]. Two pathways (front attack mechanism (front) or

Dispersion-mediated steering of organic adsorbates on a precovered silicon surface

• Lisa Pecher,
• Sebastian Schmidt and
• Ralf Tonner

Beilstein J. Org. Chem. 2018, 14, 2715–2721, doi:10.3762/bjoc.14.249

• theory; dispersion; organic/inorganic interfaces; Introduction The creation of organic/inorganic interfaces is one of the main endeavours in enhancing the application range of modern electronic devices for silicon-based technology [1][2]. One way to achieve this is covalent attachment of bifunctional

• organic molecules on bare silicon surfaces and subsequent reaction with a second molecule with both reactions being chemoselective (layer-by-layer, LbL, approach) [3][4][5]. To achieve an interface structure with predictable properties, it is important that the molecules used for the first layer show well

• minimization without symmetry constraints leads to a structure with a local C2 rotational axis resulting in symmetry-equivalent molecules 1 and 1′. Energies and Gibbs energies of adsorption were previously found to support the notion of strong covalent bonding for the [2 + 2] cycloaddition of 1 on the silicon