Electron-rich triarylphosphines as nucleophilic catalysts for oxa-Michael reactions

• Susanne M. Fischer,
• Simon Renner,
• A. Daniel Boese and
• Christian Slugovc

Beilstein J. Org. Chem. 2021, 17, 1689–1697, doi:10.3762/bjoc.17.117

• than those presented here can be achieved [22][23]. Switching to the weaker Michael acceptor acrylamide (E = −23.54 for N,N-dimethylacrylamide) [19], no useful conversions on any account were obtained. However, TMTPP performs best, giving 61 and 74% conversions with 1-propanol (b) and allyl alcohol (c

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

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

• , such as staining efficiency (362 cm2⋅C−1 at 1050 nm), fast switching time (0.5 s), high optical contrast (59% at 1500 nm), and redox stability (<8% after 4000 cycles). Poly(isoindigothiophene) 65 containing sulfonate groups in the side chain was used as an anionic photoactive polyelectrolyte in a

Substituted nitrogen-bridged diazocines

• Pascal Lentes,
• Jeremy Rudtke,
• Thomas Griebenow and
• Rainer Herges

Beilstein J. Org. Chem. 2021, 17, 1503–1508, doi:10.3762/bjoc.17.107

• . Moreover, the photoconversion yield for the E→Z isomerization is quantitative (within the detection limit of UV and NMR spectroscopy). A high efficiency in switching the biological activity off is important to avoid side effects of residual concentrations of the active form [13]. Water solubility and high

• Z→E switching efficiencies in water are additional important criteria for applications in biological environments [14]. Our previously published NAc-bridged diazocine 10c (Scheme 1, Table 1) exhibits both properties [15]. This is in stark contrast to the CH2–CH2 and S–CH2-bridged diazocines and the

• . In contrast to previous approaches, the azo cyclization (ring closure) was achieved via the oxidation of the bis-anilines 7 with mCPBA (≈60% yield). Among the nitrogen-bridged diazocines compounds 10a and 11c are water soluble and retained their high switching efficiency (≈70%) also in water. The

Cascade intramolecular Prins/Friedel–Crafts cyclization for the synthesis of 4-aryltetralin-2-ols and 5-aryltetrahydro-5H-benzo[7]annulen-7-ols

• Jie Zheng,
• Shuyu Meng and
• Quanrui Wang

Beilstein J. Org. Chem. 2021, 17, 1481–1489, doi:10.3762/bjoc.17.104

• ). However, the reaction with AlMe3 as the promotor resulted in a competing reduction of 13a to 2-bromophenylethanol (12a) that was obtained as the major product (Table 1, entry 3). Switching to the weaker Lewis acid In(OTf)3 failed to induce any intramolecular Prins cyclization (Table 1, entry 4), whilst

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

• close to optimal as possible. Certain drawbacks to using a flow-approach must also however be acknowledged. Problems may arise due to quenching requirements, the necessity for solvent switching, concentration limitations, compensating for different encountered reaction kinetics over multiple steps when

Heterogeneous photocatalytic cyanomethylarylation of alkenes with acetonitrile: synthesis of diverse nitrogenous heterocyclic compounds

• Guanglong Pan,
• Qian Yang,
• Wentao Wang,
• Yurong Tang and
• Yunfei Cai

Beilstein J. Org. Chem. 2021, 17, 1171–1180, doi:10.3762/bjoc.17.89

• ). Traditional g-C3N4 exhibited a low catalytic activity for this transformation (Table 1, entry 6). Switching from CN-K to a homogeneous organo photocatalyst such as eosin Y and 4CzIPN, led to lower yields of the desired product (Table 1, entries 7 and 8). The expensive Ru/Ir-based metal complexes gave similar

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• solar cells [49][50]. In view of the globalization of energy problems, the issues of switching to alternative energy sources are becoming increasingly relevant. Solar energy, like the majority of renewable energy sources, is environmentally friendly and has almost no negative impact on the environment

Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands

• Sergey V. Norkov,
• Anton V. Cherkasov,
• Andrey S. Shavyrin,
• Maxim V. Arsenyev,
• Viacheslav A. Kuropatov and
• Vladimir K. Cherkasov

Beilstein J. Org. Chem. 2021, 17, 273–282, doi:10.3762/bjoc.17.26

• -quinone-tetrathiafulvalene-o-quinone and o-quinone-(p-phenylene extended tetrathiafulvalene)-o-quinone were found to display switching SMM [4][5][6][7] or unique luminescent properties [8]. There are many reports describing the preparation of p-quinone derivatives annulated with a 1,3-dithiole moiety [9

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

• spectroscopy, and isothermal titration calorimetry. Results and Discussion Characterization of the flavy building block In the first step the switchability and the photostability of pelargonidin chloride (Flavy) were investigated. The switching ability of Flavy is already well-known [79][80]. Here it was

• shows the transformation of B to Cc with the fluorescence band changing from λ = 300 nm to λ = 400 nm. Formation and switching cycles of the ternary assemblies In the first step, the supramolecular assemblies were formed by mixing the photoacid 1N36S with Flavy and adding the cationic polyelectrolyte

• concentration ratio k represents the relative molar concentration of the photoacid and the Flavy molecule, as given in Equation 2: First, a system with a loading ratio of l = 0.9 and a concentration ratio of k = 1.0 was investigated. In this case, we focused on the two main switching cycles displayed in Scheme

Naphthalonitriles featuring efficient emission in solution and in the solid state

• Sidharth Thulaseedharan Nair Sailaja,
• Iván Maisuls,
• Jutta Kösters,
• Alexander Hepp,
• Andreas Faust,
• Jens Voskuhl and
• Cristian A. Strassert

Beilstein J. Org. Chem. 2020, 16, 2960–2970, doi:10.3762/bjoc.16.246

• . Also, by varying the water fractions, different phenomena can be observed and tuned by judicious choice of the substituents. Upon increasing the water content of THF solutions with NMe2 (i.e., a pure CT emitter), the luminescence exhibits intensity switching and a red-shift upon coupling/decoupling

Incorporation of a metal-mediated base pair into an ATP aptamer – using silver(I) ions to modulate aptamer function

• Marius H. Heddinga and
• Jens Müller

Beilstein J. Org. Chem. 2020, 16, 2870–2879, doi:10.3762/bjoc.16.236

• applied in combination with a fluorophore (fluorescein), a quencher (DABCYL), and complementary oligonucleotides to devise a system referred to as structure-switching signaling aptamer [40]. Based on this concept, two systems were devised to investigate whether the Im–Ag(I)–Im base pairs could be applied

• it allows triggering the function at any desired point. Further optimizations will be necessary to eliminate the effect of excess transition metal ions and to enable a more complete switching of the aptamer function. This could be possible by using other metal-mediated base pairs, based either on

• investigate the envisaged functionality of the modified structure-switching signaling aptamers (f = fluorescein, q = DABCYL). The strand shown in black is derived from the ATP/AMP-binding aptamer. System A: the aptamers 1af, 1bf, 1cf, and 1df with the complementary sequence 1q (X = imidazole, f = fluorescein

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

• hand denotes the formation of a single entity from all constituents using orthogonal binding motifs. In the self-sorting of more than two components, thus at least one ligand has to be multivalent (Figure 2). Clearly, heteromeric self-sorting has a superior value for switching because it allows for

• several assortments and thus opens up a new arena called multiple self-sorting [31], for instance, upon the addition of an external input C to AB, when B in AB is replaced by the better binding C or D: AB → AC→ AD, a process that is of interest for setting up smart reaction networks. For switching, the

• systematic indexing of examples as single, double, and multiple self-sorted systems and an evaluation of the functions during the reversible switching. Review Single self-sorting The first chapter is not yet devoted to the multiple self-sorting events, but to the rare cases where a statistical ensemble of

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

• Jannis Ludwig,
• Tobias Moje,
• Fynn Röhricht and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2589–2597, doi:10.3762/bjoc.16.210

• Jannis Ludwig Tobias Moje Fynn Rohricht Rainer Herges Otto Diels Institute of Organic Chemistry, University of Kiel, Otto-Hahn-Platz 3–4, 24098 Kiel, Germany 10.3762/bjoc.16.210 Abstract We present the synthesis and the spin switching efficiencies of Ni(II)-porphyrins substituted with

• shown that the spin switching efficiency is strongly dependent on the solvent and on the substituent at the 4-position of the pyridine unit. We now introduced thiol, disulfide, thioethers, nitrile and carboxylic acid groups and investigated their spin switching efficiency. Keywords: azopyridines; Ni(II

• the switchable ligand). This approach has been dubbed “record player” design for obvious reasons (Figure 1a). The Ni-porphyrin (“disk”) is low-spin if the azo-aryl unit (“tone arm”) is in trans configuration. Upon switching to the bent cis configuration, the lone pair of the pyridine (or imidazole

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• described with regard to their potential to form redox-switchable rotaxanes. A combination of isothermal titration calorimetry and voltammetric techniques reveals correlations between the binding energies and redox-switching properties of the corresponding pseudorotaxanes with secondary ammonium ions. For

• rotary motor [30], and an acid/base-switchable asymmetric organocatalyst [31]. In addition to MIMs switchable by light or chemical reagents, redox-switchable molecular assemblies are of particular interest, since redox switching at electrodes is considered to operate without chemical waste and

• electrochemical analytical tools, e.g., cyclic voltammetry (CV), exhibit great potential to investigate the kinetic and thermodynamic parameters of the switching processes [32][33]. Although various redox-active crown ethers have been described [14][21][34], they are not commonly implemented into crown ether

Comparative ligand structural analytics illustrated on variably glycosylated MUC1 antigen–antibody binding

• Christopher B. Barnett,
• Tharindu Senapathi and
• Kevin J. Naidoo

Beilstein J. Org. Chem. 2020, 16, 2540–2550, doi:10.3762/bjoc.16.206

• a time step of 0.001 ps. The particle mesh Ewald (PME) method was used. Nonbonded interactions were cut-off using the force-switching method from 10 Å to 12 Å, and hydrogen bonding constraints applied. During equilibration, the protein backbone and side chains were restrained (force constants of

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• Diels–Alder reaction [21][22] and (2) a chiral ligand 2-H2 for the stereocontrol [13]. Cleaving the complex under acidic conditions resulted in the desired enantiomerically enriched product 9 and enabled the recovery of the chiral ligand 2-H2 (Scheme 2) [13]. The solvent choice allowed on/off-switching

• of the stereoselectivity of the Diels–Alder reaction. In THF the stereochemically locked dimer of the hierarchical helicate was present. Here stereoselectivity was turned on. On the other hand, the highly dynamic and fast diastereomerizing/epimerizing monomer was the major species in DMF switching

• residue Li[Li3(1)3(6)3Ti2] showed only 16% ee. The yields were higher than 60%. A possible reason for the significant drop in enantioselectivity by switching from ligand 5 to 6 was due to the different dimerization behavior. The homoleptic helicate Li[Li3(6)6Ti2] shows a lower dimerization tendency

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• absorption maxima in the range of 512–543 and 529–562 nm, respectively. Of note, the largest bathochromic shifts of the absorption maxima for both series of dyes were observed in DMSO compared to the other solvents applied. Switching the solvent from PhMe to DMSO, bathochromic shifts of 31 nm for 3, 22 nm

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

• can not only be useful for enantioselective synthesis of π-bowls but also to produce novel building blocks for molecular switches, chemical machines, molecular motor, ferroelectric memories, molecular devices, and sensory materials etc. Interestingly, electronic switching, thermal transport and

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• Abstract We present the synthesis and the photochemical and catalytic switching properties of an azopyridine as a photoswitchable ligand, covalently attached to a Ni(II)-porphyrin. Upon irradiation with 530 nm (green light), the azopyridine switches to the cis configuration and coordinates with the Ni2

• activity. The rate constants in the two switching states differ by a factor of 2.2, and the catalytic switching is reversible. Keywords: catalysis; Ni(II)-porphyrins; nucleophilic catalyst; photoswitch; record player molecules; spin switch; Introduction Photoswitchable catalysis has been realized

• by coordination/decoordination to the Ni2+ ion in a Ni-porphyrin. So-called record player molecules, including a Ni(II)-porphyrin as the square planar base complex and azopyridines as photoswitchable axial ligands, were previously investigated for spin switching applications [13][14][15][16][17][18

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166

• , followed by the cleavage of the 4’-TBS protecting group gave 127 in an acceptable yield (52%). A protecting-group adjustment finalized the synthesis of 124. Notably, these authors found that switching the sulfone and aldehyde functionalities, i.e., an olefination of the aldehyde generated by the oxidation

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

• Yuqing Wang,
• Gaigai Wang,
• Anatoly A. Peshkov,
• Ruwei Yao,
• Muhammad Hasan,
• Manzoor Zaman,
• Chao Liu,
• Stepan Kashtanov,
• Olga P. Pereshivko and
• Vsevolod A. Peshkov

Beilstein J. Org. Chem. 2020, 16, 1963–1973, doi:10.3762/bjoc.16.163

• improvement allowing to obtain 12a with up to 73% ee through the reaction with dihydroquinine benzyl ether (DHQ-Bn, Table 3, entry 12). Switching to quinidine (QD), dihydroquinidine (DHQD), and their derivatives allowed to alter the stereoselectivity of the process leading to the preferred formation of

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

• Dalel El-Marrouki,
• Sabrina Touchet,
• Abderrahmen Abdelli,
• Hédi M’Rabet,
• Mohamed Lotfi Efrit and
• Philippe C. Gros

Beilstein J. Org. Chem. 2020, 16, 1722–1731, doi:10.3762/bjoc.16.144

• as the main product, with the best yield being obtained in butanol (43%, Table 1, entry 11), however, with the formation of 6b occurring only in 10% yield. Switching to microwave irradiation formed exclusively 7b in 60% yield after 3 h (Table 1, entry 13). Note, that to check the effect of a shorter

• temperature (Table 2, entry 1). Under these conditions, the expected cinnoline 8a was obtained in a low yield of 20% that could be increased up to 40% upon refluxing the mixture (Table 2, entry 2). Switching to toluene (Table 2, entry 3) did not improve the reaction outcome. However, the addition of a

Fluorohydration of alkynes via I(I)/I(III) catalysis

• Jessica Neufeld,
• Constantin G. Daniliuc and
• Ryan Gilmour

Beilstein J. Org. Chem. 2020, 16, 1627–1635, doi:10.3762/bjoc.16.135

• (64% and 56% yield, respectively, Table 1, entries 2 and 4). Fluorinated solvents such as hexafluoroisopropanol (HFIP) or ethyl trifluoroacetate (ETFA) led to similar results (52% and 50% yield, respectively, Table 1, entries 5 and 6). Switching to non-halogenated solvents such as acetonitrile or

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• reaction pathway of a TBN-mediated oxidative cyclization of β,γ-unsaturated oximes 128 was achieved by switching from the argon atmosphere to air or oxygen atmosphere and by lowering the reaction temperature to –10 °C [131]. Oximes 128 undergo cyclization to form nitrooxymethyl-substituted isoxazolines 129