Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• cyanoformate in the presence of DMPU affording an inconsequential 5.6:1 mixture of diastereomers favoring 10 (3J3H-4H 12.2 Hz vs 4.8 Hz, Scheme 1). The cyclohexadiene system of 11 was formed after deprotonation of 10 (LiHMDS) and quenching with triflic anhydride. All compounds carrying the 1,3-cyclohexadiene

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• classed as a reductive quenching cycle (Figure 4). In a reductive quenching catalytic cycle, a species must act as an oxidant to return the photocatalyst to its native oxidation state. If ET occurs such that the catalyst is oxidised, the cycle is classed as an oxidative quenching cycle (Figure 5). In an

• oxidative quenching catalytic cycle, a species must act as a reductant to return the photocatalyst to its native oxidation state. The reducing and oxidising species can be the substrate or an additive, since the classification of a catalytic cycle as either reductive or oxidative quenching considers only

• the reaction is not dependent on the catalytic cycle characterisation – either reductive or oxidative quenching. Net oxidative reactions require the presence of an oxidising agent. The advantage of photoredox net oxidative reactions, compared to conventional oxidation reactions, is that much milder

Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

• Mohammad A. Alnajjar,
• Jürgen Bartelmeß,
• Robert Hein,
• Pichandi Ashokkumar,
• Mohamed Nilam,
• Werner M. Nau,
• Knut Rurack and
• Andreas Hennig

Beilstein J. Org. Chem. 2018, 14, 1961–1971, doi:10.3762/bjoc.14.171

• quenching by photoinduced electron transfer (PET), whereas the protonated form was brightly fluorescent [31]. We report herein the synthesis and photophysical characterization of BODIPY derivatives with an aniline substituent in the meso-position to which different anchor groups have been attached, and we

• used polymer microparticles with surface-bound CB7 [66] and added them to a solution containing a mixture of 5 and 1-(aminomethyl)adamantane (AMADA). The latter was added to reduce the surface group density of the dye and prevent undesired self-quenching at high surface concentrations of the

Assessing the possibilities of designing a unified multistep continuous flow synthesis platform

• Mrityunjay K. Sharma,
• Roopashri B. Acharya,
• Chinmay A. Shukla and
• Amol A. Kulkarni

Beilstein J. Org. Chem. 2018, 14, 1917–1936, doi:10.3762/bjoc.14.166

• tanks (T1–T8) with an agitator and a jacket for maintaining the temperature. The intermediate storage tanks can be used for multiple purposes viz. preheating/precooling any reaction intermediate, mixing reagents, quenching the reaction, dilution, crystallization, reaction and can be operated in batch or

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

• Siva Sankar Murthy Bandaru,
• Darinka Dzubiel,
• Heiko Ihmels,
• Mohebodin Karbasiyoun,
• Mohamed M. A. Mahmoud and
• Carola Schulzke

Beilstein J. Org. Chem. 2018, 14, 1871–1884, doi:10.3762/bjoc.14.161

• of 22AG to derivatives 2b and 2c could be used to deduce the binding constant Kb (Figure S2, Table 3). The addition of ct DNA to the derivative 2a led to quenching of the emission intensity (Figure 8A). In contrast, a light-up effect with a factor of 3 was observed upon the addition of ct DNA to

• ][65][66]. The effect of the donor substituent on the emission quenching was supported by the strong increase of the emission quantum yield of 2c upon protonation of the amino group, that is, by the transformation of the donor to an acceptor substituent (Figure 5) [34]. Considering the water solubility

• a hypochromic effect and red shift of the absorption bands as well as emission quenching or enhancement upon addition of the nucleic acid. Moreover, the binding constants Kb, as determined from the resulting binding isotherms, are in the same range (Kb = 2.0–22 × 104 M−1, Table 3) of known DNA

Strong binding and fluorescence sensing of bisphosphonates by guanidinium-modified calix[5]arene

• Jie Gao,
• Zhe Zheng,
• Lin Shi,
• Si-Qi Wu,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2018, 14, 1840–1845, doi:10.3762/bjoc.14.157

• , we employed fluorescein (Fl) as the reporter dye according to our previously published result [26]. Fl of high brightness is strongly encapsulated into the GC5A cavity (Ka = 5.0 × 106 M−1), accompanied with a drastic complexation-induced fluorescence quenching (Ifree/Ibound = 37). Taken together

Synthesis of new tricyclic 5,6-dihydro-4H-benzo[b][1,2,4]triazolo[1,5-d][1,4]diazepine derivatives by [3⁺ + 2]-cycloaddition/rearrangement reactions

• Lin-bo Luan,
• Zi-jie Song,
• Zhi-ming Li and
• Quan-rui Wang

Beilstein J. Org. Chem. 2018, 14, 1826–1833, doi:10.3762/bjoc.14.155

• proceeded as expected under the usual reaction conditions and the desired products 13 were obtained after quenching with H2O at 0 °C. As can be seen from Scheme 4, both aliphatic and aromatic nitriles worked similarly. In light of the experimental achievements and preceding theoretical work, we rationalized

Synthesis and photophysical studies of a multivalent photoreactive Ru^II-calix[4]arene complex bearing RGD-containing cyclopentapeptides

• Sofia Kajouj,
• Lionel Marcelis,
• Alice Mattiuzzi,
• Adrien Grassin,
• Damien Dufour,
• Pierre Van Antwerpen,
• Didier Boturyn,
• Eric Defrancq,
• Mathieu Surin,
• Julien De Winter,
• Pascal Gerbaux,
• Ivan Jabin and
• Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

• + complex onto the calixarene platform does not induce any modification of the photophysical properties of the complex. In order to rule out any intramolecular quenching processes, control experiments were realized with the complex grafted onto the unmodified calixarene (conjugate 7) in the presence of free

• cyclic pentapeptide units c-[RGDfK] 8 (see Supporting Information File 1). No modification of the luminescence by intermolecular quenching was observed, confirming the absence of internal quenching in the conjugate 9. Photoreactivity of RuII-calixarene conjugate 9 The photoreactivity of Ru-TAP complexes

• excited state lifetime of conjugate 9 as function of the concentration of guanosine monophosphate (GMP, Figure 4). Stern–Volmer analyses indicate that a dynamic quenching is occurring, with a quenching rate close to the diffusion limit (kQ = 5.6 108 M−1s−1 in intensity and kQ = 5.3 108 M−1s−1 in lifetime

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• distortion and access to quenching channels to some extent. On the other hand, the appearance of new low-lying excited states associated to the π molecular orbitals typically results into efficient emission due to their larger radiative decay rates [25]. Though limited in the 1980s by their sensitive

• , thus raising the energy of quenching d–d states while lowering emissive MLCT and LC excited states. Alternatively, the use of N-deprotonable azole units has also been largely explored due to the fact that it can exert similar effects to ppy-like ligands [16]. Nevertheless, easier deprotonation of the N

• the energetic destabilization of quenching MC states [45][46]. Complexes based on C^N^N ligands Following the seminal work of von Zelewski [47][48] on platinum(II) complexes bearing C-deprotonated 2-phenylpyridines (C^N), the development of tridentate analogues has received a great deal of attention

London dispersion as important factor for the stabilization of (Z)-azobenzenes in the presence of hydrogen bonding

• Andreas H. Heindl,
• Raffael C. Wende and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 1238–1243, doi:10.3762/bjoc.14.106

• equiv) and NEt3 (65 µL, 0.44 mmol, 2.2 equiv) in THF (2 mL), pivaloyl chloride (54.4 µL, 0.437 mmol, 2.20 equiv) in THF (0.5 mL) was added dropwise at 0 °C. Then, the reaction was allowed to warm to rt while stirring for 2 h. After quenching with sat. aq. NH4Cl solution (5 mL), the aqueous phase was

Investigations of alkynylbenziodoxole derivatives for radical alkynylations in photoredox catalysis

• Yue Pan,
• Kunfang Jia,
• Yali Chen and
• Yiyun Chen

Beilstein J. Org. Chem. 2018, 14, 1215–1221, doi:10.3762/bjoc.14.103

• benziodoxole have opposite effects for the radical alkynylation, we first conducted the fluorescence quenching experiments of tolylacetylenic benziodoxole derivatives 3a–f and found none of them oxidatively quenched the photoexcited Ru(bpy)32+* complex (see Supporting Information File 1, Scheme S1). We next

• oxidative quenching step by benziodoxole radical (step 2), the electron-donating substituents on BI’-alkynes are both beneficial, while the electron-withdrawing substituents have opposite effects. Conclusion In conclusion, we have developed and investigated novel alkynylbenziodoxole derivatives as radical

• isolated yields. Mechanistic investigations of alkynylbenziodoxole for radical acceptor and oxidative quenching reactivity. Yields are isolated yields. N/P = not performed. The role of alkynylbenziodoxole derivatives for radical alkynylation in photoredox catalysis. Supporting Information Supporting

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• ), subsequent quenching by the addition of methanol, yielded dihydro derivative 103 (Scheme 18). In 1978, in order to examine heteroatomic influences on the possible generation of 9C–10π homoaromatic dianions, Paquette’s group described the synthesis and reducibility of benzo-fused-homo-2-methoxyazocines from

Polysubstituted ferrocenes as tunable redox mediators

• Sven D. Waniek,
• Jan Klett,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2018, 14, 1004–1015, doi:10.3762/bjoc.14.86

• application as redox mediator (Scheme 2) [55][56]. Ferrocenyl esters 1–4 are synthetically accessible via the acids of 1 [45][46], 2 [57], 3 and 4 [54] in a direct selective metalation of ferrocene [54][57][58][59][60], quenching with carbon dioxide, followed by esterification [45][46][47][48][54]. The 1,1

Volatiles from three genome sequenced fungi from the genus Aspergillus

• Jeroen S. Dickschat,
• Ersin Celik and
• Nelson L. Brock

Beilstein J. Org. Chem. 2018, 14, 900–910, doi:10.3762/bjoc.14.77

• quenching of cation J with water (box in Scheme 2), suggesting that this enzyme is responsible for the biosynthesis of 15 in A. fischeri. Therefore, the enzyme XP_001265719 is likely responsible for the biosynthesis of 19 and its byproducts. The biosynthetic origin of the observed traces of monoterpenes is

Investigating radical cation chain processes in the electrocatalytic Diels–Alder reaction

• Yasushi Imada,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 642–647, doi:10.3762/bjoc.14.51

• luminescence quenching experiments [19]. With such an understanding in hand, radical ion chain processes could be further optimized to realize greener transformations. We have been developing anodic cycloadditions [20][21][22][23][24][25] enabled by lithium perchlorate/nitromethane electrolyte solution [26

Continuous multistep synthesis of 2-(azidomethyl)oxazoles

• Thaís A. Rossa,
• Nícolas S. Suveges,
• Marcus M. Sá,
• David Cantillo and
• C. Oliver Kappe

Beilstein J. Org. Chem. 2018, 14, 506–514, doi:10.3762/bjoc.14.36

• through a continuous addition of reagent streams, quenching, liquid–liquid extraction, or even filtration stages, thus avoiding the handling of unstable intermediates [35][36][37]. In this article we present an integrated continuous-flow procedure for the preparation of 2-(azidomethyl)oxazoles 7 starting

Carbohydrate inhibitors of cholera toxin

• Vajinder Kumar and
• W. Bruce Turnbull

Beilstein J. Org. Chem. 2018, 14, 484–498, doi:10.3762/bjoc.14.34

• tryptophan fluorescence quenching assay to show that octavalent lactose-based dendrimer 34 (Figure 16) had a Kd value of 33 µM as compared to monovalent lactose derivative having a Kd value of 18,000 µM [51]. Hence, compound 34 displayed 545 fold more potency per lactose unit than monovalent lactose. In

Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)

• Thanh-Tuân Bui,
• Fabrice Goubard,
• Malika Ibrahim-Ouali,
• Didier Gigmes and
• Frédéric Dumur

Beilstein J. Org. Chem. 2018, 14, 282–308, doi:10.3762/bjoc.14.18

• quenching processes occurring at high current density such as triplet–triplet annihilation and exciton–polaron annihilation. 3. Diphenylsulfone-based emitters Concerning the design of blue TADF emitters, diphenylsulfone is the third most widely studied acceptor in the literature, followed by triarylboron

Fluorogenic PNA probes

• Tirayut Vilaivan

Beilstein J. Org. Chem. 2018, 14, 253–281, doi:10.3762/bjoc.14.17

• fluorescence dye and quencher to be in close proximity, resulting in quenching of the dye. Binding to the complementary DNA target opened the hairpin structure and restored the fluorescence. In Armitage’s design [42], the entire beacon was purely PNA, while in the Ortiz design [41], PNA was employed as the DNA

• make a close contact. However, based on their detailed comparative studies between stemless PNA and DNA beacons, the Boston Probes group argued that the quenching was more likely due to hydrophobic and electrostatic interactions between the fluorophore and the quencher. Nevertheless, different

• another fluorophore may be placed in close proximity in the probe molecule, thereby maximizing the interactions between the two dyes and leading to a more effective quenching. Duplex formation will alter the interaction if one of the dyes can intercalate into the duplex or form a more stable end-stacking

Aminomethylation/hydrogenolysis as an alternative to direct methylation of metalated isoquinolines – a novel total synthesis of the alkaloid 7-hydroxy-6-methoxy-1-methylisoquinoline

• Benedikt C. Melzer,
• Jan G. Felber and
• Franz Bracher

Beilstein J. Org. Chem. 2018, 14, 130–134, doi:10.3762/bjoc.14.8

• 7-benzyloxy-6-methoxyisoquinoline with Knochel–Hauser base, followed by cuprate-mediated methylation gives the target alkaloid directly, but separation from the educt is cumbersome. Quenching the metalated intermediate with Eschenmoser’s reagent gives an easy to clean tertiary benzylamine, which

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• finally oxidized by an in situ generated superoxide radical anion to form the respective sulfoxide. In contrast, Fraile, Aleman and co-workers use the organic photocatalyst Eosin Y and propose a different mechanism for their method (Scheme 15b). Based on several quenching experiments, they suggest that

• . Rearomatization via hydrogen atom abstraction by the former generated superoxide radical anion leads to the desired 2-substituted benzothiazole. The authors observed a green colour of the reaction mixture indicating the formation of [Ru(bpy)3]3+. Therefore, they suggest an oxidative quenching cycle, but an

• as photocatalyst (Scheme 32) [67]. Instead of using dioxygen as sacrificial oxidant and basic additives for proton scavenging, they installed a second catalytic cycle for proton reduction deliberating dihydrogen as byproduct. The reaction is proposed to proceed via a reductive quenching of the

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• owing to enhanced amphiphilicity of the hybrid molecule inflicted by the hydrophobic character of the fluorescent label and the formation of aggregates which resulted in self-quenching. To circumvent these problems, a longer hydrophilic linker and a less hydrophobic fluorescent group were required. An

• antagonist) and the fluorescence intensity of 25 and its tetraacylated counterpart was comparable with the fluorescence of the labeling reagent alone. Aggregation-mediated fluorescence quenching was not observed which confirmed the advantage of application of highly hydrophilic linker molecules and non

Metal-mediated base pairs in parallel-stranded DNA

• Jens Müller

Beilstein J. Org. Chem. 2017, 13, 2671–2681, doi:10.3762/bjoc.13.265

• base pair (Scheme 4e) within regular B-DNA did not include any data on the stabilizing effect of the Ag(I) ion coordination but unequivocally confirmed metal-mediated base pair formation via the quenching of the intrinsic fluorescence of MePC [61]. The 2PyrPC–Ag(I)–C and 3PyrPC–Ag(I)–C base pairs

A concise flow synthesis of indole-3-carboxylic ester and its derivatisation to an auxin mimic

• Marcus Baumann,
• Ian R. Baxendale and
• Fabien Deplante

Beilstein J. Org. Chem. 2017, 13, 2549–2560, doi:10.3762/bjoc.13.251

• , temperature and reagent stoichiometry – selected results are presented in Table 1. Although DMF and MeCN were shown to be excellent solvents for the reaction (Table 1, entries 3–6, 10, 15–23, and 26) we encountered difficulties in efficiently extracting the product upon quenching the reactions (1 M HCl

• positioned run-off. At flow rates of 0.5–1.2 mL/min emanating from the main reactor this unit performed reliably giving excellent quenching and separation. However, at higher flow rates issues were encountered with incomplete partitioning (some emulsion formation) of the biphasic mixture resulting in the

• the problematic mixing chip with various configured T- and Y-connectors but this immediately gave other issues due to incomplete quenching which resulted in poor product recovery and associated contamination. A more straightforward approach proved to be to introduce a flow stratification zone prior to

Pyrene–nucleobase conjugates: synthesis, oligonucleotide binding and confocal bioimaging studies

• Artur Jabłoński,
• Yannic Fritz,
• Hans-Achim Wagenknecht,
• Rafał Czerwieniec,
• Tytus Bernaś,
• Damian Trzybiński,
• Krzysztof Woźniak and
• Konrad Kowalski

Beilstein J. Org. Chem. 2017, 13, 2521–2534, doi:10.3762/bjoc.13.249

• 3nπ* state decays nonradiatively to the ground state, directly or via internal conversion to lower triplet states. Thus, the 3nπ* state provides a path for efficient depopulation of the emissive 1ππ* singlet state and, thus, for quenching of fluorescence. In the hydroxy derivatives 4 and 5, such low

• pyrene 1ππ* state). Thus, intersystem crossing between these two states can be efficient giving rise to also efficient radiationless depopulation of the emissive singlet state relative to aliphatic analogues, in that quenching 3nπ* states are not present. Interactions with oligonucleotides Compounds 2–5