Reversible switching of arylazopyrazole within a metal–organic cage

• Anton I. Hanopolskyi,
• Soumen De,
• Michał J. Białek,
• Yael Diskin-Posner,
• Liat Avram,
• Moran Feller and
• Rafal Klajn

Beilstein J. Org. Chem. 2019, 15, 2398–2407, doi:10.3762/bjoc.15.232

• limited dimensions of cage cavities can also be used for arresting the growth of polycondensates at an early stage, thereby making it possible to isolate labile species. For example, Fujita and co-workers demonstrated the stabilization of cyclic trimers of siloxanes inside small self-assembled cages [14

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

• that this plasticity of side chains in the active site of CotB2 plays not only an important role in stabilization and hence propagation of carbocations. In future experiments, it would be interesting to investigate the influence of double or triple mutations within the active site. Moreover, it would

Small anion-assisted electrochemical potential splitting in a new series of bistriarylamine derivatives: organic mixed valency across a urea bridge and zwitterionization

• Keishiro Tahara,
• Tetsufumi Nakakita,
• Alyona A. Starikova,
• Takashi Ikeda,
• Masaaki Abe and
• Jun-ichi Kikuchi

Beilstein J. Org. Chem. 2019, 15, 2277–2286, doi:10.3762/bjoc.15.220

• could not contribute to the relatively large thermodynamic stability of 1a+ and 1b+. This indicated that the common stabilization mechanism for the covalently linked conventional MV species is applicable to the present urea-bridged MV species 1+. The highest occupied molecular orbitals (HOMOs) of the

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

• the color changed to yellow, and the intensity was enhanced (Figure 6b). Such a blue shift of ESIPT fluorescence was already reported and it is ascribed to suppression of the stabilization of the excited zwitterionic species through solvent rearrangement and/or further conformational changes of the

Click chemistry towards thermally reversible photochromic 4,5-bisthiazolyl-1,2,3-triazoles

• Chenxia Zhang,
• Kaori Morinaka,
• Mahmut Kose,
• Takashi Ubukata and
• Yasushi Yokoyama

Beilstein J. Org. Chem. 2019, 15, 2161–2169, doi:10.3762/bjoc.15.213

• electron-withdrawing cyano groups than when they are electron-donating methoxy groups. Keywords: aromatic stabilization energy; diarylethene; ruthenium(I) catalysed Huisgen cyclization; terarylene; thermally reversible photochromism; Introduction Diarylethenes are one of the most widely investigated

• among the photochromic families [1][2][3]. They are known to show thermally irreversible photochromism. However, some of them are thermally reversible [4]: (1) when the aromatic stabilization energy of the aromatic rings is large [5]; (2) when the substituent groups on the ring-closing carbon atoms are

• related families of diarylethenes, are largely thermally reversible [10][12] although some are irreversible when the aromatic stabilization energy of the aromatic rings is small [11]. Their syntheses are usually carried out by the sequential construction of the central aromatic ring at the final stage [10

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• [TCNQ]−· radical anion, dragging the second [TCNQ]− near to the cavity by the help of the electrostatic stabilization supplied by the 1,2,3-triazolium cations, coupling of the two [TCNQ]−· anion radicals in the cavity and rapid formation of the sigma-connected dimer, reduction of the photogenerated

Synthesis and properties of sulfur-functionalized triarylmethylium, acridinium and triangulenium dyes

• Marco Santella,
• Eduardo Della Pia,
• Jakob Kryger Sørensen and
• Bo W. Laursen

Beilstein J. Org. Chem. 2019, 15, 2133–2141, doi:10.3762/bjoc.15.210

• ][39]. This observation is in agreement with the much stronger cation stabilization of the dialkylamino group compared to the methoxy group. The ability of the alkylthio group to stabilize carbenium ions, given by the Hammet σp+ value [40], on the other hand is quite similar to the methoxy group or

Fluorinated azobenzenes as supramolecular halogen-bonding building blocks

• Esther Nieland,
• Oliver Weingart and
• Bernd M. Schmidt

Beilstein J. Org. Chem. 2019, 15, 2013–2019, doi:10.3762/bjoc.15.197

• substituting azobenzenes in the ortho-positions to the N=N bond with electron-withdrawing fluorine substituents [45][46], the red-shifting of the n→π* transitions enables selective addressing of both the E- and Z-isomer using visible light. Stabilization of the n-orbitals in the Z-isomers leads to a very high

• transition state (TS, see Supporting Information File 1, Table S8). In the B3LYP computations this value is larger than for the corresponding Z-isomer and leads to a stabilization of the TS in polar solvents [46]. The bistable character is obviously weakened upon improving the halogen bonding properties

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

• Vera Deneva,
• Georgi Dobrikov,
• Aurelien Crochet,
• Daniela Nedeltcheva,
• Katharina M. Fromm and
• Liudmil Antonov

Beilstein J. Org. Chem. 2019, 15, 1898–1906, doi:10.3762/bjoc.15.185

• , the stabilization between the E and K forms is a result of the competition between the strength of the hydrogen bonding in the enol tautomer and the effect of simple alkyl substitution in the keto form skeleton. The calculations also suggest that the efficient switching towards the enol form can be

• and experimentally, the tautomeric state and complexation abilities of compound 6, where only one carbonyl group in the ionophore part is present (Scheme 2). It is expected that the enol tautomer stabilization would be achieved in the neutral state as a result of the strong intramolecular hydrogen

• bonding between the tautomeric OH group and the carbonyl group in the ionophore part. The complex formation, depending on the size and charge of the metal ion, should shift the tautomeric equilibrium towards the keto tautomer and should provide stabilization of the complex. To the best of our knowledge

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

• formation of the heterometallic [CsKA'2] from the mixture of [KA'] and CsI, even though in low yield, owes its realization to the entropic benefit of a mixed metal system, but even more importantly to the formation of intermolecular M…CH3 contacts, permitting the formation and stabilization of a sheet

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer

• Jason Yin Hei Man and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2019, 15, 1829–1837, doi:10.3762/bjoc.15.177

• , suggesting intercomponent stabilization could play an important role in directing higher level structures in mechanically interlocked molecules, reminiscent to the intra-strands interactions that stabilize high-order structures in (bio)polymers. Conclusion In summary, complex hetero[n]rotaxanes have been

The cyclopropylcarbinyl route to γ-silyl carbocations

• Xavier Creary

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

• cation (a cation containing hypercoordinated carbon) that could be derived from protonation of bicyclobutane [20]. Another potential mode of stabilization is by an interaction of the cationic center with the adjacent strained cyclobutyl bonds as in 7b. A second class of carbocations that this article

• will deal with is the so-called “electron-deficient” carbocation, i.e., carbocations 9 (Figure 1) substituted with electron-withdrawing groups E [21]. Many studies have shown that such cations can indeed be generated and that they can derive stabilization by a variety of mechanisms. Chief among these

• Figure 3 are M062X/6-311+G** calculated structures and energies of cations 27 and 24, which are distinct energy minima, along with the transition state 28 which connects these two cations. Cation 27 derives most of its stabilization from the phenyl group, while the TMS group in the 3-position provides no

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D–π–)₂A fluorescent dyes

• Keiichi Imato,
• Toshiaki Enoki,
• Koji Uenaka and
• Yousuke Ooyama

Beilstein J. Org. Chem. 2019, 15, 1712–1721, doi:10.3762/bjoc.15.167

• electron-withdrawing ability of the azine ring lowers the LUMO energy level of the (D–π–)2A fluorescent dyes. Consequently, the fact revealed that the bathochromic shift of the ICT-based photoabsorption band in the order of OUY-2 < OUK-2 < OUJ-2 is attributed to the stabilization of the LUMO energy level

• photoabsorption band in the order of OUY-2 < OUK-2 < OUJ-2 is attributed to a stabilization of the LUMO energy level due to the increase in the electron-withdrawing ability of the azine ring in the order of pyridyl < pyrazyl < triazyl. Conclusion To gain insight into the photophysical and electrochemical

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

Water inside β-cyclodextrin cavity: amount, stability and mechanism of binding

• Stiliyana Pereva,
• Valya Nikolova,
• Silvia Angelova,
• Tony Spassov and
• Todor Dudev

Beilstein J. Org. Chem. 2019, 15, 1592–1600, doi:10.3762/bjoc.15.163

• fellow waters from the (n − 1) clusters (Figure 2 and Figure 3). It can be concluded (similarly to the previously examined α-CD hydration [19]) that the first water molecule coordinated to the narrow rim OH groups plays a pivotal role in the formation and stabilization of the β-CD polyhydrates acting as

Synthesis and conformational preferences of short analogues of antifreeze glycopeptides (AFGP)

• Małgorzata Urbańczyk,
• Michał Jewgiński,
• Joanna Krzciuk-Gula,
• Jerzy Góra,
• Rafał Latajka and
• Norbert Sewald

Beilstein J. Org. Chem. 2019, 15, 1581–1591, doi:10.3762/bjoc.15.162

• covering the entire main chain. The observed unordered conformation is in agreement with the previously reported results, which suggested that one repeating unit comprising the Ala-Thr(GalNAc)-Ala motif is not enough to provide interresidual interaction, required for stabilization of the ordered

Transient and intermediate carbocations in ruthenium tetroxide oxidation of saturated rings

• Manuel Pedrón,
• Laura Legnani,
• Maria-Assunta Chiacchio,
• Pierluigi Caramella,
• Tomás Tejero and
• Pedro Merino

Beilstein J. Org. Chem. 2019, 15, 1552–1562, doi:10.3762/bjoc.15.158

• –O distance increased to 3.00 Å in TS2 and to 3.15 Å in TS3 (similar data were found in acetonitrile, see Supporting Information File 1) clearly indicating a delay in the formation of the C–O bond. This situation is compatible with the stabilization of a developing positive charge at the carbon atom

• place in two separate events. The stabilization of the above-mentioned transient carbocation can be achieved by introducing heteroatoms. The ELF analysis corresponding to the oxidation of tetrahydrofuran (Figure 3A) again showed a typical one-step-two-stage situation. In this case, the gap between the H

• enhanced by the presence of heteroatoms that stabilize the developing positive charge by resonance, as in the case of tetrahydrofuran and tetrahydrothiophene. Moreover, the presence of a nitrogen atom provides enough stabilization to be located as an energy minimum and to be captured experimentally [26

A heteroditopic macrocycle as organocatalytic nanoreactor for pyrroloacridinone synthesis in water

• Piyali Sarkar,
• Sayan Sarkar and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2019, 15, 1505–1514, doi:10.3762/bjoc.15.152

• issue for the stabilization of the activated complex by a hydrophobic catalyst [31]. Again, the efficiency of an organocatalyst could be enhanced by downsizing the catalyst at nanorange distribution (i.e., nanoreactor) [13][14]. This is because a nanoreactor allows for precise interactions with the

• reactants. In fact, encapsulation can result in the stabilization of a specific transition state by stripping it out from solvent molecules [13][14]. Hence, in aqueous medium, the syntheses of nanoreactors with a covalent organic framework is important, which is indeed a difficult task due to their large

• stabilization. Consequently, the presented BATA-MC-catalyzed protocol demonstrates a general applicability furnishing a variety of multisubstituted acridines. Confirmation of structures All products (4,5-dihydropyrrolo[2,3,4-kl]acridinones 4a–p and pyrrolo[2,3,4-kl]acridinones 7a–c) were characterized by using

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

• DTT 1 to DSS 4, with stronger stabilization of the S2 transition which is coherent with the large atomic contribution from the heteroatoms to the involved molecular orbitals HOMO-1 and LUMO (vide supra). We can conclude that the theoretically calculated transitions S1 and S2 are reflected in the

• 3.91 eV for DTT 1 to 3.67 eV for DSS 4 due to a stabilization of the HOMO energy level with increasing number of selenium atoms in the heteroacene (vide infra). The extinction coefficients are as well sensitive to the heteroatom in the bridge for pair DTT 1/DTS 2 (26,800 to 22,100 L mol−1 cm−1) and DST

Bambusuril analogs based on alternating glycoluril and xylylene units

• Tomáš Lízal and
• Vladimír Šindelář

Beilstein J. Org. Chem. 2019, 15, 1268–1274, doi:10.3762/bjoc.15.124

• reflecting the presence of conformers 1b-2 and 1b-1. However, the ratio of these conformers is 82:1 in favor of 1b-1 which translates to the energy difference of 2.04 kcal mol−1. Stabilization of the 1b-1 conformer can be attributed to the intramolecular hydrogen bonding interaction between the oxygen atom

Mechanochemical amorphization of chitin: impact of apparatus material on performance and contamination

• Thomas Di Nardo and
• Audrey Moores

Beilstein J. Org. Chem. 2019, 15, 1217–1225, doi:10.3762/bjoc.15.119

• systematic study of the effects of a number of medium parameters onto a model reaction, namely the amorphization of chitin where interchain stabilization is greater than 250 kJ/mol based on density functional theory (DFT) calculation [58]. We explored the role of the material of the jar and the ball, ball

Molecular recognition using tetralactam macrocycles with parallel aromatic sidewalls

• Dong-Hao Li and
• Bradley D. Smith

Beilstein J. Org. Chem. 2019, 15, 1086–1095, doi:10.3762/bjoc.15.105

• macrocycle. Supramolecular picture of the amide-bond-formation step that clips tetralactam A around a biscarbonyl template to form a [2]rotaxane. Complex stabilization due to guest back folding and aromatic stacking with the surrounding tetralactam macrocycle. Acknowledgements We are grateful for funding by

Coordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands

• Jennifer Klose,
• Tobias Severin,
• Peter Hahn,
• Alexander Jeremies,
• Jens Bergmann,
• Daniel Fuhrmann,
• Jan Griebel,
• Bernd Abel and
• Berthold Kersting

Beilstein J. Org. Chem. 2019, 15, 840–851, doi:10.3762/bjoc.15.81

• drastically alter its structural properties and reactivities. Prominent examples are the cis-bromination of α,β-unsaturated carboxylato ligands [2], regioselective Diels–Alder reactions of encapsulated dienoate ligands [3], and the stabilization of unusual co-ligand conformations, respectively [4]. The

Strong hyperconjugative interactions limit solvent and substituent influence on conformational equilibrium: the case of cis-2-halocyclohexylamines

• Camila B. Francisco,
• Cleverton S. Fernandes,
• Ulisses Z. de Melo,
• Roberto Rittner,
• Gisele F. Gauze and
• Ernani A. Basso

Beilstein J. Org. Chem. 2019, 15, 818–829, doi:10.3762/bjoc.15.79

• halogens, as mentioned before, the pronounced ea preference observed in our case led us to investigate the specific effects that may be responsible for this behavior. Delocalization, electrostatic and steric interactions In order to determine which effects are responsible for the stabilization of each

• , the sum was made of all hyperconjugative stabilization energies (Eij) involving both bonding and antibonding orbitals, as well as the energies of nitrogen and halogen lone-pair interactions (LPN and LPX, respectively), resulting in 22 variables corresponding to all the bonds of the structure of the

• respective orbitals (C–X bonds and antibonds) increases in the same way; however, the LPX follows the reverse order, with a decrease in the donor ability as LPF > LPCl > LPBr > LPI. These observations allow us to analyze which specific orbitals are responsible for the great stabilization of the ea conformer

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

• Andrejs Šišuļins,
• Jonas Bucevičius,
• Yu-Ting Tseng,
• Irina Novosjolova,
• Kaspars Traskovskis,
• Ērika Bizdēna,
• Huan-Tsung Chang,
• Sigitas Tumkevičius and
• Māris Turks

Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41

• -deazapurine class, which could be explained by a better stabilization of the ICT excited state by the solvatic shell. A decrease of QY accompanied by a high red shift of the emission maxima with increasing polarity of the surrounding media is a typical characteristic for the enhanced ICT of the excited states