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

• the meta-stable cis-form relaxes back thermally to the more stable trans from (Figures S50 and S51 in Supporting Information File 1). Thus, the cis–trans isomerization appears to be not constrained by the [Cd2L]2+ fragment, as revealed by the similar half-lives (τ1/2 cis–trans free deprotonated

• + entity, and trans-configured azo groups. NMR and UV–vis studies clearly show that the complexes retain their mixed-ligand nature in the solution state. Irradiation of the Cd complex 1 with a LED UV lamp leads to a trans-to-cis isomerization which appears to proceed within the coordination sphere of the

• irradiated with a UV LED lamp (365 nm) for 1 to 30 s after irradiation. Concentration of solutions: 10−5 M. Synthesis of complexes 1–9. Cis/trans isomerization process of the bound azo-carboxylato co-ligand in [Cd2L(μ-azo-H)]ClO4 (1) in acetonitrile mediated by irradiation with 365 nm UV light. The amino

A diastereoselective approach to axially chiral biaryls via electrochemically enabled cyclization cascade

• Hong Yan,
• Zhong-Yi Mao,
• Zhong-Wei Hou,
• Jinshuai Song and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2019, 15, 795–800, doi:10.3762/bjoc.15.76

• groups including aryltrimethylsilane (3p), silyl ether (3q–s), ester (3t) and cylic ketal (3u). Note that all the diastereomers were separable by flash column chromatography. Heating a solution of the major isomer of 3n in MeCN at 80 °C for 4 h did not lead to isomerization, suggesting that the

• in MeCN at 80 °C for 4 h resulted in a mixture of diastereomers in a ratio of 3:1. These results suggest that the sterically demanding substituents at R1 and R2 positions (cf. Table 1) are critical to ensure good stereoselectivity during the product formation and to prevent isomerization after the

Azologization of serotonin 5-HT₃ receptor antagonists

• Karin Rustler,
• Galyna Maleeva,
• Piotr Bregestovski and
• Burkhard König

Beilstein J. Org. Chem. 2019, 15, 780–788, doi:10.3762/bjoc.15.74

• photo-induced trans–cis isomerization representing the time of birth of the azobenzene photoswitch. Benefiting of their accessible synthesis, large change in polarity and geometry upon switching, excellent photochromic properties and tuneability, azobenzenes are amongst the most widely used photochromic

• such an extent, that no new maximum representing the cis-isomer was observed and thus cis–trans isomerization only occurs thermally and is not triggerable by irradiation with visible light. Back-isomerization was triggered by irradiation with visible light (5a, 5b, 16a, 16b, 23, and 28) of the

• indicated wavelength or by thermal relaxation (5a, 5b, 12a, 16a–d, 23, and 28). The irradiation times were determined by following the UV–vis spectrum upon isomerization until no more changes in absorption were observed and the photostationary state (PSS) was reached. The points of intersection in the

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

• group vibration bands in the infrared spectra. At the same time, structuring and isomerization occur in layers generating changes in their physical properties, in particular, the decrease of layer permeability for atmospheric air. In its turn, this leads to the transition of the oxidation from a kinetic

Synthesis of functionalized diazocines for application as building blocks in photo- and mechanoresponsive materials

• Widukind Moormann,
• Daniel Langbehn and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 727–732, doi:10.3762/bjoc.15.68

• were investigated by NMR and UV–vis spectroscopy and the results are listed in Table 1. Photostationary states (PSS) as well as half-lives (t1/2) were determined in acetonitrile at 300 K and 298.15 K, respectively. The (cis → trans) and (trans → cis) isomerization were achieved by irradiation into the

• appropriate n–π* bands at 385 and 530 nm. As a result of electronic decoupling the absorption bands are well separated and the photostationary states of diazocines 4–7 are considerably improved compared to 3,3’- (2) and 4,4’-diaminodiazocine 3 (Figure 3). The (cis → trans) isomerization of diazocines 4–7 was

• achieved after 2 min of irradiation at 385 nm in yields of 74–85%. All trans-diazocines were converted quantitatively to the cis-configuration either by thermal relaxation or by irradiation at 530 nm. In general, the (trans → cis) isomerization can be accomplished with wavelengths between 520 and 620 nm

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• D thus accomplishing the final connectivity of the three components. Enol/carbonyl tautomerization gives the isolated β-ketoenamide KE with E-configuration being the result of the intramolecular acyl transfer. Even after storage of β-ketoenamides there is no evidence that an isomerization to the

Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts

• Grzegorz Mlostoń,
• Małgorzata Celeda,
• Katarzyna Urbaniak,
• Marcin Jasiński,
• Vladyslav Bakhonsky,
• Peter R. Schreiner and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2019, 15, 497–505, doi:10.3762/bjoc.15.43

• -aromatization of the imidazole ring. The same mechanism governs sulfur-transfer reactions with cycloaliphatic thioketones yielding the corresponding imidazole-2-thiones [13]. The isomerization of N-oxides 1 into the corresponding imidazol-2-ones can be easily performed by treatment with acetic anhydride at room

• 8b–d in 66%, 62%, and 39% yield, respectively. As pointed out in the introduction, one of the most typical reactions of 2-unsubstituted imidazole N-oxides is their isomerization to imidazol-2-ones. In many reported cases, this transformation can be performed by treatment with acetic anhydride

• ppm belongs to HN(3). The 13C NMR spectrum confirmed the structure of 9 by the signal of the C(2)=O group found at 153.0 ppm. The corresponding band in the IR spectrum appeared at 1702 cm−1as the strongest absorption. Thermal isomerization of 7b was also tested. However, boiling in bromobenzene for 15

Aqueous olefin metathesis: recent developments and applications

• Valerio Sabatino and
• Thomas R. Ward

Beilstein J. Org. Chem. 2019, 15, 445–468, doi:10.3762/bjoc.15.39

• multiple tedious steps, primarily because metal complexes’ impurities in the final product may cause isomerization or decomposition of the products and may be toxic. The latter is a very critical issue for the pharmaceutical industry, as the amount of ruthenium in APIs (active pharmaceutical ingredients

• -metathesis of allyl alcohol (59) and the cis–trans isomerization of cis-butenedienol (Z-58). Metathesis catalysts bearing quaternary ammonium groups provide an attractive alternative to classical ruthenium catalysts. Although they do not represent a great improvement in terms of catalytic activity, they

• diallylmalonate 31 in DCM (Scheme 11). Upon reaction completion, the catalyst is extracted from the organic reaction mixture with D2O and (re)-used for the isomerization of cis-butenediol Z-58 in water. Recently the removal of a water-soluble catalyst from reaction mixtures was also achieved with catalyst 12

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• alkylidenecyclopropanes. The transformation of cyclopropenes into alkylidenecyclopropanes has been achieved through different strategies (Scheme 1). The first one relies on the isomerization of the olefin in alkylcyclopropenes A from the endocyclic to the exocyclic position (Scheme 1, reaction 1) [16][17][18]. Owing to

• substituent at C1. Whereas conjugation with the phenyl group (R = Ph) provides the driving force for the base-promoted isomerization of 1-benzyl-3,3-difluorocyclopropene (A’, R = Ph) into the corresponding benzylidene(gem-difluoro-cyclopropane) (B’) [18], methylene(gem-difluorocyclopropane) (B’’, R = H) is

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

• reactants. In the reaction of monovinyl-POSS with allylbenzene, CM was accompanied by double bond migration, which results in reduction of the isolated yield of the CM product (85%) and the formation of minor amounts (15%) of 1-propenylbenzene. No similar isomerization was observed in the reaction of POSS

Synthesis of 1,2-divinylcyclopropanes by metal-catalyzed cyclopropanation of 1,3-dienes with cyclopropenes as vinyl carbene precursors

• Jesús González,
• Alba de la Fuente,
• María J. González,
• Laura Díez de Tejada,
• Luis A. López and
• Rubén Vicente

Beilstein J. Org. Chem. 2019, 15, 285–290, doi:10.3762/bjoc.15.25

• refluxed in toluene (24 h) partial isomerization was observed (endo/exo = 1:1.6). This behavior can be attributed to the high substitution at one of the alkenes, which might lead to sterically overcrowded transition states required for the rearrangement [27]. Besides, the diastereoisomeric mixture of 3j

Olefin metathesis in multiblock copolymer synthesis

• Maria L. Gringolts,
• Yulia I. Denisova,
• Eugene Sh. Finkelshtein and
• Yaroslav V. Kudryavtsev

Beilstein J. Org. Chem. 2019, 15, 218–235, doi:10.3762/bjoc.15.21

• for the formation of NB–COE copolymer [95]. Some results regarding the cis/trans-isomerization of double bonds in the MCM process were obtained [85][87][89]. In the systems PNB–PCOE (68% cis)–Gr1 and PBD–cis-olefin-containing polyurethane (cis-PU)–Gr2, cis-double bonds partly transform to a more

• thermodynamically stable trans-configuration, which is well-known for olefin metathesis [85][89]. The cis/trans-isomerization is observed for homodyads in MCM and even in the course of the homopolymer–catalyst interaction as a result of self-metathesis reactions that do not directly influence the copolymer

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• (Scheme 11). More recently, Olivier-Bourbigou and Mauduit demonstrated the ability of unsymmetrical N-cycloalkyl Ru–indenylidene catalysts for the selective self metathesis of linear α-olefins to longer internal linear olefins in the absence of additives to prevent isomerization [35]. Catalyst 91 with a

• distribution with no isomerization was observed without the use of any additive even after 24 h of reaction performed at 50 °C under neat conditions. N-Alkyl substituents possessing functionalities or heteroatoms In 2001, the Fürstner group reported on phosphine-containing ruthenium complexes having

Cross metathesis-mediated synthesis of hydroxamic acid derivatives

• Shital Kumar Chattopadhyay,
• Subhankar Ghosh and
• Suman Sil

Beilstein J. Org. Chem. 2018, 14, 3070–3075, doi:10.3762/bjoc.14.285

• 6d–f, respectively. Considerable isomerization (1:1 by 1H NMR) of the CM-product 6d to the corresponding styrene derivative was noticed when HG-II was used in place of G-II. 6e behaved similarly. Reaction with the styrene derivative 4g resulted in low conversion to the CM product 6g (57%). Styrene

Ring-closing-metathesis-based synthesis of annellated coumarins from 8-allylcoumarins

• Christiane Schultze and
• Bernd Schmidt

Beilstein J. Org. Chem. 2018, 14, 2991–2998, doi:10.3762/bjoc.14.278

• defined order. One class of products, pyrano[2,3-f]chromene-2,8-diones, were inaccessible through direct RCM of an acrylate, but became available from the analogous allyl ether via an assisted tandem catalytic RCM/allylic oxidation sequence. Keywords: coumarins; heterocycles; isomerization; olefin

• catalyst A in dichloromethane at ambient temperature, higher dilution and after prolonged reaction time. For the synthesis of furanocoumarins 3 the allyl ethers 9 were first subjected to a Ru hydride-catalyzed double bond isomerization [55][56] to furnish enol ethers 10 as inseparable mixtures of

• substitution pattern 15 was investigated starting from acrylate 12d (Scheme 2). The isomerization of the 8-allyl substituent to a prop-1-enyl substituent under the conditions used for the synthesis of precursors 10 (Table 2) stopped at 50% conversion. Higher catalyst loading and an increased reaction

MoO₃ on zeolites MCM-22, MCM-56 and 2D-MFI as catalysts for 1-octene metathesis

• Hynek Balcar,
• Martin Kubů,
• Naděžda Žilková and
• Mariya Shamzhy

Beilstein J. Org. Chem. 2018, 14, 2931–2939, doi:10.3762/bjoc.14.272

• ‘ acidity and accessibility of the catalytic species on the surface. On the other hand the supports‘ acidity decreases the selectivity to the main metathesis product C14 due to an acid-catalyzed double bond isomerization (followed by cross metathesis) and oligomerization. 6MoO3/2D-MFI(26) with a lower

• in considerable amounts. It is a consequence of the 1-octene double bond isomerization followed by cross metathesis. Moreover, a certain amount of oligomers (mainly dimers) were also observed in the reaction mixtures. Both isomerization and oligomerization are due to the acidic character of the

• the selectivity due to isomerization and/or oligomerization seems to be an unavoidable cost for this activity enhancement. It is known for molybdenum oxide catalysts, that with increasing Mo loading the catalytic activities increase up to maximum value [6][10]. At higher loadings the molybdenum oxide

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

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

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

• noting, that compounds 3a–h have strictly cis-configuration of SO2Ar group and a vinyl substituent at C2 carbon. It should be mentioned that palladium-catalyzed isomerization of such (arylsulfonyl)allenes 2 into trans-butadienes 3 was described recently [23]. Herein, we have developed a novel metal-free

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• few byproducts were noticed. A control experiment omitting the ethyl nitroacetate (4) allowed us to identify amongst these: the oxazole derivative 31 resulting from an isomerization of 25 as well as alcohol 32 resulting from an oxidation of compound 25. Accordingly, this greatly dampened our hope to

• amount of gold(I) in warm toluene provided us with the oxazoline 40 in an 80% yield. However, this compound turned out to be unstable, either on standing, probably because of an autoxidation, as reported in other instances [27], or in CDCl3, probably because of acid traces. To achieve its isomerization

• chemistry aiming at the preparation of oxazole-bearing α-amino esters which was of interest per se. Indeed, the previously unreported acid-catalyzed conditions to achieve the isomerization of the methylene-bearing oxazoline 40 into oxazole 41 should be useful in many other instances. In any case, as

Oxidative and reductive cyclization in stiff dithienylethenes

• Michael Kleinwächter,
• Ellen Teichmann,
• Lutz Grubert,
• Martin Herder and
• Stefan Hecht

Beilstein J. Org. Chem. 2018, 14, 2812–2821, doi:10.3762/bjoc.14.259

• double bond isomerization in addition to ring-closure, has been investigated. Electrochromism was observed in almost all cases, with the major pathway being the oxidatively induced cyclization of the open isomers. The influence of the ring size (to lock the reactive antiparallel conformation) as well as

• components for optical memories [3][4]. In addition to photochemistry, the isomerization of DAEs can also be triggered by electrochemical means, therefore providing a stimulus orthogonal to light [5]. Electrochemically induced isomerization of DAEs is almost exclusively based on oxidation. Either cyclization

• [5][6][7][8][9][10][11][12][13] or cycloreversion [14][15][16][17][18][19][20][21] can be observed, while correlation of both reaction modes to the molecular structure is still under discussion [22][23][24][25][26]. There are only few reports about reductive isomerization, each involving the ionic

Synthesis of mono-functionalized S-diazocines via intramolecular Baeyer–Mills reactions

• Miriam Schehr,
• Daniel Hugenbusch,
• Tobias Moje,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2018, 14, 2799–2804, doi:10.3762/bjoc.14.257

• ]. The back isomerization is initiated quantitatively with light within the range of 500–660 nm. Hence, the trans-to-cis isomerization can be performed with red light which is important for medical applications, because blood-supported tissue is transparent in the far red region [27]. For the iodo

• trans isomer are between 1–7 days. These properties are ideal for applications in photopharmacology where the more bulky cis state is the inactive form and the trans isomer is the active configuration. Cis–trans isomerization of mono-functionalized S-diazocines 1–5. UV spectra of the S-diazocine 4 in

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• opening of the heteroring, (Scheme 7). The process involves isomerization through olefin bond migration proceeding Z-selectively. Conclusion The ring-opening metathesis (ROM) of some ring-constrained, unsaturated bicyclic frameworks has been studied in the presence of commercially available ruthenium

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• catalysts for chemists because they efficiently mediate difficult organic reactions under mild conditions [46][47][48][49][50][51]. In some catalysis mediated by B12 enzymes, the high reactivity of the adenosyl radical is exploited for isomerization. The microenvironments provided by the apoenzymes activate

• , and Irdfppy system was used for radical-mediated isomerization reactions. Visible-light irradiation of diethyl 2-bromomethyl-2-phenylmalonate produced the phenyl-migrated product (Scheme 10) [104]. The product distribution highly depended on the solvents. The yield of phenyl-migrated products relative

• obtained through isomerization with 1,2-migration of the ester groups. The B12-TiO2 hybrid catalyst can be regarded as a good alternative for conventional radical-involved organic syntheses using tin compounds. Recently, we discovered that the B12 derivative 1 can mediate trifluoromethylation and

Synergistic approach to polycycles through Suzuki–Miyaura cross coupling and metathesis as key steps

• Sambasivarao Kotha,
• Milind Meshram and
• Chandravathi Chakkapalli

Beilstein J. Org. Chem. 2018, 14, 2468–2481, doi:10.3762/bjoc.14.223

• substrate 117, which was subjected to RCM with the aid of G-II catalyst 2 to produce a mixture of products 119 and 121 in combined 47% yield. It should be noted that the resulting product 121 was obtained through isomerization of the terminal double bond followed by RCM. Later, oxidation of diols 119 and

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• )propane), and bpy as ligands afforded the olefin isomerization product as the major product. Further screening of the reaction conditions revealed that the amount of AlMe3 was critical: the product yield increased with decreasing AlMe3 to 1.5 equiv. The concentration of 11a also affected the efficiency of

• the reaction, and the isomerization of olefins could be suppressed at lower concentrations of 11a, affording the desired 12a-Me in 58% yield. With the addition of 1 equiv of CsF, the carboxylation was further accelerated to give 12a-Me in 71% yield. Using optimized reaction conditions, the substrate

• discovered the one-pot synthesis of coumarin derivatives via hydrocarboxylation/alkene isomerization/cyclization reactions (Scheme 22) [49]. A key of the sequential reactions is a use of aromatic alkynes bearing a momo-protected hydroxy group at the ortho position on the aromatic ring (23). The corresponding

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

• Tobias Fiedler,
• Michał Barbasiewicz,
• Michael Stollenz and
• John A. Gladysz

Beilstein J. Org. Chem. 2018, 14, 2354–2365, doi:10.3762/bjoc.14.211

• ; crystal structures; homeomorphic isomerization; hydrogenation; in/out isomers; metathesis; phosphine boranes; Introduction We have found that a variety of metal complexes with trans-phosphine ligands of the formula P((CH2)mCH=CH2)3 (1; m = 4–14) undergo threefold interligand ring closing alkene

• 2 and 3: in,in, out,out, and in,out (identical to out,in). The first two, as well as the degenerate in,out pair, can rapidly interconvert by a process termed homeomorphic isomerization [26][27], which is akin to turning the molecules inside out. Readers are referred to earlier publications in this

• triarylphosphorus bridgeheads and p-phenylene containing tethers that are long enough to allow rapid homeomorphic isomerization. The precursor 18·2(=O) was prepared by a threefold Williamson ether synthesis in surprisingly high yields (61% in,in/out,out and in,out combined) [50][51], likely aided by the geminal