1,4-Dithianes: attractive C2-building blocks for the synthesis of complex molecular architectures

• Bram Ryckaert,
• Ellen Demeyere,
• Frederick Degroote,
• Hilde Janssens and
• Johan M. Winne

Beilstein J. Org. Chem. 2023, 19, 115–132, doi:10.3762/bjoc.19.12

• chemoselective and stereospecific mild hydrodesulfurization with Raney nickel in acetic acid affords the target compound 59 as a single Z-diastereomer. Interestingly, glacial acetic acid proved to be the only solvent that could avoid both undesired overreduction and cis–trans isomerization of the alkene bond. It

Catalytic aza-Nazarov cyclization reactions to access α-methylene-γ-lactam heterocycles

• Bilge Banu Yagci,
• Selin Ezgi Donmez,
• Onur Şahin and
• Yunus Emre Türkmen

Beilstein J. Org. Chem. 2023, 19, 66–77, doi:10.3762/bjoc.19.6

• single diastereomers. This reaction outcome was attributed to a potential cis–trans isomerization of the C–N double bond upon iminium formation (Scheme 4). In this respect, the mixing of imine 18 with the α,β-unsaturated acyl chloride 6 is expected to form the iminium ion 20a with Z-configuration. A

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• the activation energies for both cis–trans-isomerization and for the transformation of vinylcyclopropanes into cyclopentenes. Both processes could occur by a C–C-bond homolysis to form a diradical. Computational studies by Gety, Hrovat, and Borden indicated that there would be a preference for

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• triene system, which is susceptible to cis–trans isomerization, have been longstanding problems in the area of inthomycins. The problems are more acute for the construction of enantioenriched β-hydroxycarbonyl units as evident from the recent reports [19][20][21]. Since the pioneering works of Henaff and

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

• under air to form the disulfide. Investigation on the spin switching performance of the Ni(II)-porphyrins The spin switching performance of a record player molecule depends on different parameters: 1. the coordination strength of the axial ligand, 2. the effectivity of the cis–trans isomerization, since

• NMR experiments. For 1f and 1i the cis/trans ratio was obtained from integration of the signals of H-11, which differ in cis and trans configuration. (Supporting Information File 1, Figure S14). However, NMR spectroscopy was not suitable to determine the cis–trans isomerization yields of 1e, 1g, 1h

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

• influence of the solvent on the switching efficiency was evaluated by UV–vis (Figure S2, Supporting Information File 1) and NMR experiments (Figure 2). It is important to note that there are two ways to define the switching efficiency of record player molecules: 1. the cis–trans isomerization of the

• , the thermal relaxation time for the cis→trans isomerization in THF was determined by 1H NMR spectroscopy. Similar to previous record player systems a long half-life of the metastable cis isomer of about 505 d (25 °C, THF-d8) was determined (Figure S5 in Supporting Information File 1). Thus, the

• proton H-11 (1H NMR, 600 MHz, THF-d8, 318 K), which are an indicator for the cis–trans isomerization of the azo unit of porphyrin 1, in the PSS at 530 nm (green) and 435 nm (violet-blue). The signal at 6.54 ppm belongs to the cis species while the signal at 6.41 represents the trans isomer. c) 1H NMR

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• shed more light on some mechanistic pathways and set the key foundation for the further use as photoinitiators or photocatalysts. In 1961, Hammond and co-workers studied the cis/trans isomerization of the piperylenes (1,3-pentadienes) 61 and 62 in the presence of carbonyl compounds as photosensitizers

• (Scheme 15) [50]. Among the compounds tested, 1-naphthaldehyde (63) provided a photostationary mixture rich in the trans-diene (trans/cis ratio ≈ 13). A year later, the same group further studied the cis/trans isomerization of the piperylenes 61 and 62 utilizing energy transfer from the triplet states of

• , reductant 51, and benzaldehyde derivatives 52–54 for the polymerization of the methacrylates 59. Proposed mechanism of the photomediated atom transfer radical polymerization employing the benzaldehyde derivatives 52–54, respectively, as the photocatalysts. cis/trans isomerization employing triplet states of

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

• Roland Löw,
• Talina Rusch,
• Tobias Moje,
• Fynn Röhricht,
• Olaf M. Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1815–1821, doi:10.3762/bjoc.15.175

• , while the functional groups are protruding upright and freestanding from the central carbon atoms. Azobenzene derivatized TATA’s are known to exhibit extremely fast cis→trans isomerization on metal surfaces, via a peculiar non-adiabatic singlet→triplet→singlet mechanism. We now prepared norbornadienes

• ; quadricyclane; self-assembled monolayers; TATA platform; thermal isomerization; TOTA platform; Introduction Recently, we discovered that the thermochemically forbidden cis–trans isomerization of azobenzenes can be efficiently catalysed by a very peculiar mechanism on bulk gold [1]. In heterogeneous catalysis

• extension from simple cis→trans isomerization to other thermochemically forbidden reactions such as [2 + 2] cycloreversions. Moreover, a deeper understanding of the non-adiabatic, catalytic process and successful application of the concept to the QC→NBD isomerization could contribute to the elucidation of

An azobenzene container showing a definite folding – synthesis and structural investigation

• Abdulselam Adam,
• Saber Mehrparvar and
• Gebhard Haberhauer

Beilstein J. Org. Chem. 2019, 15, 1534–1544, doi:10.3762/bjoc.15.156

• the other, caused by irradiation with UV light. For the cis→trans isomerization counterclockwise rotations are found. Furthermore, quantum chemical calculations reveal that the energy of the cis,cis-isomer is only slightly higher than the energy of the cis,trans-isomer. This effect can be explained by

Diazocine-functionalized TATA platforms

• Roland Löw,
• Talina Rusch,
• Fynn Röhricht,
• Olaf Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1485–1490, doi:10.3762/bjoc.15.150

• Abstract Recently, it has been shown that the thermochemical cis→trans isomerization of azobenzenes is accelerated by a factor of more than 1000 by electronic coupling to a gold surface via a conjugated system with 11 bonds and a distance of 14 Å. The corresponding molecular architecture consists of a

• ordered monolayers on Au(111) surfaces. Keywords: cis–trans isomerization; diazocine; molecular switch; photochrome; self-assembled monolayers; TATA platform; Introduction Catalysts increase chemical reaction rates by lowering the activation energies and thus create more favorable reaction pathways [1

• (cis) and 493 nm (trans) (Figure 2). The photostationary states of 1 and 2 were determined in toluene-d8 by 1H NMR measurements (Table 2). Optimal wavelengths for the cis→trans isomerization are 405 nm (1: 53% trans, 2: 65% trans). Back-isomerization to the cis-isomer with 525 nm is nearly quantitative

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

• 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

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

• 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

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

• 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

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

• -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

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

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

• 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

Are boat transition states likely to occur in Cope rearrangements? A DFT study of the biogenesis of germacranes

• José Enrique Barquera-Lozada and
• Gabriel Cuevas

Beilstein J. Org. Chem. 2017, 13, 1969–1976, doi:10.3762/bjoc.13.192

• [64]. The stability of the wave functions of all the transition states was checked. An unrestricted wave function was used to calculate the activation energy of the cis/trans isomerization of the (Z,E)-germacranolide. All energies were reported with zero-point energy corrections and all TS geometries

• predict the conformation of a germacrene. Interestingly, the (Z,E)-germacranes are significantly more stable than (E,E)-germacranes. Then, cis/trans isomerization can only happen in one way, (E,E)-germacranes → (Z,E)-germacranes. Moreover, this isomerization cannot be thermally activated because of the

Benzothiadiazole oligoene fatty acids: fluorescent dyes with large Stokes shifts

• Lukas J. Patalag and
• Daniel B. Werz

Beilstein J. Org. Chem. 2016, 12, 2739–2747, doi:10.3762/bjoc.12.270

• isomerization has to take place. To access the benzothiadiazole (BTD) fatty acid 3 with just one conjugated double bond we made use of the Wittig reaction starting with commercially available aldehyde 1. As expected, the (Z)-isomer was the major product; thus, we performed a subsequent cis–trans isomerization

• presence of a Lewis acid and DIBAL at low temperatures. MnO2-mediated oxidation afforded the respective aldehyde that was immediately transformed by Wittig reaction. Iodine-catalyzed cis–trans isomerization yielded the desired fatty acid 7 in 35% over three steps (Scheme 2). The analogue with three

Tuning of tetrathiafulvalene properties: versatile synthesis of N-arylated monopyrrolotetrathiafulvalenes via Ullmann-type coupling reactions

• Vladimir A. Azov,
• Diana Janott,
• Dirk Schlüter and
• Matthias Zeller

Beilstein J. Org. Chem. 2015, 11, 860–868, doi:10.3762/bjoc.11.96

• regioselective functionalization of TTF, however, remains problematic due to the presence of four identical attachment sites. Incorporation of the TTF moiety in macrocycles usually leads to poorly separable mixtures of cis/trans isomers [7][8][9]. Even if separation is possible, TTFs are prone to cis/trans

• isomerization, which can be induced by light [10] or traces of acid [11]. These problems are aggravated by the fact that each reversible oxidation–reduction cycle of the TTF moiety always leads to formation of cis/trans isomer mixtures. Bis-pyrrolotetrathiafulvalenes 2 and monopyrrolotetrathiafulvalenes (MPTTFs

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• optically pure compounds was determined by using NMR and comparing their electronic circular dichroism data with model compounds of known absolute configurations. Mechanisms for cis–trans-isomerization of silybin are proposed and supported by quantum mechanical calculations. Keywords: 2,3-cis-silybin

• propose a mechanism for the cis–trans-isomerization processes. Results and Discussion Chemistry In our previous work on the enzymatic kinetic resolution of silybin [4][5], BF3∙OEt2 in EtOAc was found to catalyze the transesterification of silybin to yield not only 23-O-acetylsilybin (2, ca. 90%), but two

• NMR coupling constants and a comparison of their ECD spectra with model compounds with well-defined absolute configurations. Moreover, the absolute configuration of these novel 2,3-cis- and 10,11-cis-isomers of silybin enabled us to propose mechanisms for the cis–trans isomerization of silybin

An investigation of the observed, but counter-intuitive, stereoselectivity noted during chiral amine synthesis via N-chiral-ketimines

• Thomas C. Nugent,
• Richard Vaughan Williams,
• Andrei Dragan,
• Alejandro Alvarado Méndez and
• Andrei V. Iosub

Beilstein J. Org. Chem. 2013, 9, 2103–2112, doi:10.3762/bjoc.9.247

• ensuing experimental and computational (DFT) results favor the former, pre-existing, explanation. Keywords: chiral amines; cis/trans isomerization; imine isomerization; imine reduction; reductive amination; Introduction A class of chiral compounds drawing ever more attention is α-chiral amines (chiral

• reference [51].) Reduction of this imine, regardless of the starting cis/trans ratio, resulted in the same amine product dr. It was then proposed that this occurred because of in situ cis/trans isomerization but no further evidence was offered, here we follow up on this point. Harada also noted that protic

True and masked three-coordinate T-shaped platinum(II) intermediates

• Manuel A. Ortuño,
• Salvador Conejero and
• Agustí Lledós

Beilstein J. Org. Chem. 2013, 9, 1352–1382, doi:10.3762/bjoc.9.153

Spin state switching in iron coordination compounds

• Philipp Gütlich,
• Ana B. Gaspar and
• Yann Garcia

Beilstein J. Org. Chem. 2013, 9, 342–391, doi:10.3762/bjoc.9.39

• primary step of LD-LISC is a photochemical reaction on the ligand molecules, for instance a photo-induced cis/trans-isomerization on 4-styrylpyridine (stpy) as a ligand, e.g., in [Fe(II)(stpy)4(NCS)2], which modulates the ligand field strength at the metal center and eventually leads to spin state

Amino-substituted diazocines as pincer-type photochromic switches

• Hanno Sell,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2013, 9, 1–7, doi:10.3762/bjoc.9.1

• as directed motion at the molecular level [2][3], the geometry change and the force induced during cis–trans isomerization has to be coupled to the environment. In the macroscopic world, therefore, machines are made from stiff materials. Azobenzene, however, is a rather floppy molecule. Both phenyl

Partial thioamide scan on the lipopeptaibiotic trichogin GA IV. Effects on folding and bioactivity

• Marta De Zotti,
• Barbara Biondi,
• Cristina Peggion,
• Matteo De Poli,
• Haleh Fathi,
• Simona Oancea,
• Claudio Toniolo and
• Fernando Formaggio

Beilstein J. Org. Chem. 2012, 8, 1161–1171, doi:10.3762/bjoc.8.129

• /trans isomerization can be phototriggered by irradiation at about 260 nm [absorption maximum of the -C(=S)NH- π→π* electronic transition]. (iii) It may act as a minimalist, effective quencher for any type of protein and nonprotein fluorophores. Recently, based on the aforementioned characteristics of

• ][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. Among these properties, we highlight the following: (i) The thioamide NH group is more acidic than that of its oxygenated counterpart and consequently it is a stronger H-bonding donor. (ii) Its cis