Iodine-mediated hydration of alkynes on keto-functionalized scaffolds: mechanistic insight and the regiospecific hydration of internal alkynes

• Zachary Lee,
• Brandon R. Jones,
• Nyochembeng Nkengbeza,
• Michael Phillips,
• Kayla Valentine,
• Alexis Stewart,
• Brandon Sellers,
• Nicholas Shuber and
• Karelle S. Aiken

Beilstein J. Org. Chem. 2019, 15, 2747–2752, doi:10.3762/bjoc.15.265

• 8 were observed after 21 h, where new signals emerged and the substrate’s resonances disappeared. However, signals for 10 were also observed, suggesting that as soon as the intermediate 9 was formed, it was converted to the final hydration product 10. Quenching of this reaction mixture cleanly

• the signals observed in Figure 1b and Figure 1c confirmed that the I2- and ICl-mediated hydrations occurred via the same intermediate. Furthermore, quenching of the ICl-facilitated reaction also resulted in the formation of compound 10. Importantly, the existence of the α-iodo intermediate 9 holds

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• molecular aggregation in the solid state causes fluorescence quenching [16]. In recent years, we have coined diversity-oriented syntheses of functional chromophores by multicomponent strategies [17][18], opening accesses to substance libraries for systematic studies of structure–property relationships on

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• intense as the emitted energy increases, (iii) the intensities of the emission lines but not their wavelength vary with the UCNP size, as the surface quenching becomes the most efficient deactivation path for small nanoparticles. Therefore, the assessment of the upconversion quantum yields (UCQY) is a hot

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• of 0.2–0.4, reaching in some cases values as high as 0.5–0.6. Laser-flash photolysis provided evidence for the existence of excited triplet states. The dyes form fluoroboronate complexes with fluoride anions, leading to the observation of the quenching of the long-wavelength emission band and

• these dyes such as intramolecular charge-transfer processes and tunable red-shifted emission bands. Generally, the so far investigated borylated arylisoquinoline dyes show principally fluorescence quenching (on-off switching) on the formation of the corresponding fluoroboronate complexes [37]. Herein

• for dye 17). These transients showed lifetimes in the microsecond range (τT = 4.2 μs (16) and 4.4 μs (17)), were efficiently quenched by oxygen (bimolecular quenching constant kq ca. 1.1–1.2 × 109 M−1s−1), and led to the energy-transfer triplet-sensitization of β-carotene (observation of the triplet

Safe and highly efficient adaptation of potentially explosive azide chemistry involved in the synthesis of Tamiflu using continuous-flow technology

• Cloudius R. Sagandira and
• Paul Watts

Beilstein J. Org. Chem. 2019, 15, 2577–2589, doi:10.3762/bjoc.15.251

• vial at room temperature. Azide 5 selectivity was reduced with time in the vial. Therefore, the development of a suitable quenching procedure may be helpful. The TBAA procedure seems to be a promising NaN3 procedure replacement when considering the aforementioned anhydrous telescoping due to its

Synthesis of novel sulfide-based cyclic peptidomimetic analogues to solonamides

• José Brango-Vanegas,
• Luan A. Martinho,
• Lucinda J. Bessa,
• Andreanne G. Vasconcelos,
• Alexandra Plácido,
• Alex L. Pereira,
• José R. S. A. Leite and
• Angelo H. L. Machado

Beilstein J. Org. Chem. 2019, 15, 2544–2551, doi:10.3762/bjoc.15.247

• reported for solonamides. Keywords: antivirulence drug; bacteria; macrocyclization; pathoblocker; quorum quenching; Introduction The cyclodepsipeptides called solonamides A and B are natural molecules extracted from the marine bacterium Photobacterium halotolerans [1][2] (Figure 1). They are able to

In search of visible-light photoresponsive peptide nucleic acids (PNAs) for reversible control of DNA hybridization

• Lei Zhang,
• Greta Linden and
• Olalla Vázquez

Beilstein J. Org. Chem. 2019, 15, 2500–2508, doi:10.3762/bjoc.15.243

• effect of the scrambled PNA 19 is the opposite, i.e., signal decrease. We determined a slightly lower fluorescence value than in the case of BHQ-ssDNA; this can be probably attributed to the quenching ability of both PNA probes [52]. Along these lines, the quenching ability of oF4Azo-containing PNA was

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• be responsible for the fluorescence quenching in the Z-form. A comparison of the kinetic traces recorded on the maximum of the excited state absorption band in the three analyzed solvents (Figure 6) demonstrates that the excited state decay time decreases on going from acetonitrile to toluene, and

Sugar-derived oxazolone pseudotetrapeptide as γ-turn inducer and anion-selective transporter

• Sachin S. Burade,
• Sushil V. Pawar,
• Tanmoy Saha,
• Navanath Kumbhar,
• Amol S. Kotmale,
• Manzoor Ahmad,
• Pinaki Talukdar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2019, 15, 2419–2427, doi:10.3762/bjoc.15.234

• the rate of quenching in fluorescence at λem = 535 nm (λex = 455 nm) was monitored using transporter 2a by creating a Cl– gradient across the lipid membrane by applying NaCl in the extravesicular buffer (Figure S14 in Supporting Information File 1). The compound 2a showed a significant decrease in the

Targeted photoswitchable imaging of intracellular glutathione by a photochromic glycosheet sensor

• Xianzhi Chai,
• Hai-Hao Han,
• Yi Zang,
• Jia Li,
• Xiao-Peng He,
• Junji Zhang and
• He Tian

Beilstein J. Org. Chem. 2019, 15, 2380–2389, doi:10.3762/bjoc.15.230

• broad and strong absorption makes the 2D MnO2 nanosheets a potential energy acceptor for the fluorophores which are stacked on the nanosheets plane, leading to the fluorescence quenching through FRET mechanism [32][34]. The transmission electron microscopy (TEM) image of the prepared product revealed

• effective FRET between the attached Glyco-DTE and 2D MnO2, which again suggested the close stacking of Glyco-DTE to the nanosheet surface. Aggregation-caused quenching might be another reason for the fluorescence quenching because of the close distance between fluorescence molecules when absorbed on the

• ” sensor towards GSH, which is illustrated as fluorescence turn-on and sequential on-off cycles. Besides, the quenching of the reporter fluorescence by MnO2 contributes to a significantly lowered background signal, which makes it an excellent material for intracellular precision imaging. Cell-targeted

Current understanding and biotechnological application of the bacterial diterpene synthase CotB2

• Ronja Driller,
• Daniel Garbe,
• Norbert Mehlmer,
• Monika Fuchs,
• Keren Raz,
• Dan Thomas Major,
• Thomas Brück and
• Bernhard Loll

Beilstein J. Org. Chem. 2019, 15, 2355–2368, doi:10.3762/bjoc.15.228

• carbocation (3) and finally the quenching of the carbocation by a base or water [16][17]. TPSs can be divided into two distinct classes, which are distinguished by their substrate activation mechanism. Whereas ionization of an isoprenoid diphosphate is caused by hydrolysis of the pyrophosphate by a trinuclear

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

• negative value of the HOMO energy level and/or the oxidation potential [15], but it is also influenced by other factors. Nonradiative quenching (e.g., bond rotation) can effectively contribute to depopulation of the fluorophore’s excited state [28], yielding a lower quantum yield. However, the rational

Functionalization of 4-bromobenzo[c][2,7]naphthyridine via regioselective direct ring metalation. A novel approach to analogues of pyridoacridine alkaloids

• Benedikt C. Melzer,
• Alois Plodek and
• Franz Bracher

Beilstein J. Org. Chem. 2019, 15, 2304–2310, doi:10.3762/bjoc.15.222

• metalation at C-5 with TMPMgCl∙LiCl at −40 °C. Quenching with various electrophiles gives a broad range of 5-substituted products, which are building blocks for the synthesis of heterocyclic natural products and analogues thereof. In combination with a Parham-type cyclization a novel approach to pyrido[4,3,2

• 5-subsituted products (Scheme 1). Quenching of metalated 9d with aldehydes 11a–d while warming to room temperature led to the formation of the expected racemic secondary alcohols 12a–d in moderate to good yields (50–66%, Scheme 1). Any attempts to improve the yields failed. The use of 2.2

• equivalents of base, longer reaction times, higher or lower temperatures did not increase the yields. In order to explore additional metalations at other positions than C-5 or imaginable halogen dance reactions [24] during the metalation process, we performed a D2O quenching experiment after the metalation

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• quenching is prevented thanks to the design of the fluorophore [42]. It should be noted that the largest dendrimers, in particular generation 4, display very large two-photon absorption cross-sections (σ2 up to 55,900 GM), which are comparable to those measured for the best quantum dots [43]. Thus these

• the previous examples of dendrimers bearing as terminal functions compounds having TPA properties is soluble in water, and thus they cannot be used for biological purposes. Furthermore, many fluorophores are sensitive to the presence of water, which induces in many cases a quenching of the

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• aggregation (aggregation-caused quenching (ACQ)). The luminogenic materials with AIE have attracted much interest since Tang et al. reported the AIE concept [12]. The introduction of photo-switching ability in the system will be interesting for creating new AIE systems. In addition, organic photochromic

• was dropped to the UV light irradiated crystal 1o (Supporting Information File 3, Movie 2). The rate of fluorescence quenching (τ1/2 is less than 0.2 s) in the crystalline state is much faster than those observed in solutions. This is attributed to the degree of condensation which is much higher in

• the crystalline state. The mechanism of the fast quenching is expected to be related to the amplification of photo-switching of a photochromic organic nanoparticle system as well as the crystalline system reported by Fukaminato and co-workers [29][30]. A detailed study of the amplification will be

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• catalysis is mainly [Ru(bpy)3]2+ [21], due to its strong MLCT (metal-to-ligand charge transfer) absorption, the excellent yield of its triplet state and the long lifetime, the versatile redox behavior (Ru3+ vs Ru+) in quenching processes and the chemical and photochemical robustness. Despite their positive

Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition

• Yulia V. Khoroshunova,
• Denis A. Morozov,
• Andrey I. Taratayko,
• Polina D. Gladkikh,
• Yuri I. Glazachev and
• Igor A. Kirilyuk

Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200

• moieties, and careful basification resulted in intramolecular cyclisation givnig 5b,c with a yield of 51% and 42%, respectively. Nitrones 5a–c readily react with 4-pentenylmagnesium bromide. Quenching of the reaction mixtures with water under aerobic conditions leads to partial oxidation of resultant N

Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments

• Guojuan Li,
• Chunying Fan,
• Guo Cheng,
• Wanhua Wu and
• Cheng Yang

Beilstein J. Org. Chem. 2019, 15, 1601–1611, doi:10.3762/bjoc.15.164

• enantiopure P5A-DPA and P5A-Py. It was found that the CD signals were enhanced by aggregation. P5A-DPA showed aggregation-induced emission enhancement, while P5A-Py showed aggregation-induced emission quenching, accompanied by excimer emission when aggregating in water and THF mixed solution. Keywords

• to aggregation-caused quenching (ACQ), as was demonstrated by UV–vis absorption and CD studies. For compound P5A-Py, however, the fluorescence intensity continuously decreased when adding water into the THF solutions, and at 70% water content, a new emission peak at 540 nm was observed which was

• the THF solution. P5A-DPA and P5A-Py showed an enhancement of the CD signals by adding water due to restriction of the conformers’ rotations by aggregation. P5A-DPA showed a fluorescence enhancement when less than 50% of water was added, while P5A-Py showed emission quenching and excimer emission when

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• (Table 2, entry 4), we conducted reactions with the series of arenes (Table 3). An excess of methanol was used for quenching of reaction mixtures instead of water. This treatment produced dimethoxyphosphoryl groups [(MeO)2P=O] in the reaction products, rather than the acidic group [(HO)2P=O] in compounds

• complex mixtures of oligomeric compounds. In the same reaction with benzene, allene 1b afforded alkene Z-11n in high yield (Scheme 5). The use of morpholine for quenching of the superacidic reaction mixture gave amide Z-11o in the reaction of 1a with benzene (Scheme 6). We also conducted a large-scale one

• cations A, B, and F–H. Large-scale one-pot solvent-free synthesis of amides 6a,b from the corresponding propargylic alcohols. AlCl3-promoted hydroarylation of allene 1b by benzene leading to alkene Z-11n. Reaction of allene 1a with benzene under the action of AlCl3 followed by quenching of the reaction

2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes

• Li-Li Wang,
• Yi-Kuan Tu,
• Huan Yao and
• Wei Jiang

Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146

• macrocycle, which make it conformationally adaptive to maximize the binding affinities. In addition, the macrocycle shows fluorescent quenching when adding the chloride metal complexes in its solution and may be used as a fluorescent sensor for the detection of these coordination complexes. Keywords: host

• maximum of 1 is located at 350 nm (Figure S22, Supporting Information File 1). It is known that the binding of metal ions could cause fluorescence quenching through photo-induced electron transfer [44]. Indeed, the fluorescence intensity of 1 is quenched gradually upon addition of TBA[AuCl4] (Figure 6a

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• luminescent dyes. Fluorescein, eosin Y, rose bengal, tetraphenylporphine sulfonate and sulfonated aluminum phthalocyanine were employed as classical aggregation-induced quenching dyes. 2-(p-Toluidinyl)naphthalene-6-sulfonic acid and 1-anilinonaphthalene-8-sulfonic acid were selected as representatives of

• with carboxylated bipyridyl ligands (Ru(dcbpy)3), were screened as model guests on account of the desired strong host–guest binding affinity (Scheme 2). Fl, EY, RB, TPPS and AlPcS4 were employed as classical aggregation-caused quenching (ACQ) dyes; 2,6-TNS and 1,8-ANS were selected as intramolecular

• as well-demonstrated fluorescence quenchers acting through a photoinduced electron transfer (PET) mechanism [8][28][29], we hypothesize an electron transfer-induced quenching in the GC5A–Fl complex as underlying mechanism. The binding stoichiometry between GC5A and Fl was determined to be 1:1

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

• dehydrocoupling with ZnCl2 and CuCl2. Selenophene precursor 10 itself was readily obtained in 68% yield from selenophene (9) in a one-pot procedure by successive lithiation with n-BuLi and quenching with trimethylsilyl chloride and iodine, respectively. We reacted biselenophene 11 with K2S as sulfur source and

Anomeric sugar boronic acid analogues as potential agents for boron neutron capture therapy

• Daniela Imperio,
• Erika Del Grosso,
• Silvia Fallarini,
• Grazia Lombardi and
• Luigi Panza

Beilstein J. Org. Chem. 2019, 15, 1355–1359, doi:10.3762/bjoc.15.135

• position. The analogues were obtained by hydroboration of proper open-chain terminal alkenes that, after quenching with water, spontaneously afforded cyclic boronic acids with hemiacetal-like structures. Keywords: antitumor agents; boron neutron capture therapy; boronic acid; hydroboration; sugar analogue

• the desired product 7 by the simple treatment of 6 with an excess of borane-THF complex (5 molar equiv) followed by quenching with water, while in the same conditions compound 5 again gave extensive decomposition. These conditions allowed the isolation of the cyclic anomeric boron analogue 7 in

Efficient resolution of racemic crown-shaped cyclotriveratrylene derivatives and isolation and characterization of the intermediate saddle isomer

• Sven Götz,
• Andreas Schneider and
• Arne Lützen

Beilstein J. Org. Chem. 2019, 15, 1339–1346, doi:10.3762/bjoc.15.133

• belongs to the saddle isomer, its isolation and characterization was necessary. First, we tried to generate 1-S by heating a DMSO solution of (rac)-1 to 200 °C for 5 minutes and quenching the mixture by pouring it into ice water according to the procedure established by Luz for the methoxy-substituted CTV

• corresponds to the saddle conformer and is marked with 1-S. a) 1H NMR spectrum of the neat crown isomers of (rac)-1 in CD3OD (400 MHz, 298 K); b) 1H NMR spectrum in CD3OD (400 MHz, 298 K) of a sample of (rac)-1 after heating it to 200 °C in DMSO and quenching the solution by pouring it into an ice water