Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• of prospective applications of indigo photoswitches. Keywords: indigoid dyes; photochemistry; photophysics; photoswitching; E–Z isomerization; Review Historical milestones in the development of photochromic indigo derivatives 1954: first reported photochromic indigo derivative – N,N'-diacetylindigo

• irradiation with orange light in several solvents [40]. However, due to the technical limitations of the spectrometer, Pummerer and Marondel were not able to detect the short-living Z-11a in aromatic solvents such as benzene, bromobenzene and pyridine. Nevertheless, the E–Z isomerization of 11a was observed

• , 11a, 14a and the twisting angles or the C=C stretching frequencies was found. Therefore, the hypsochromic shift observed during the E–Z isomerization of N,N'-disubstituted indigos cannot be explained by a larger twisting angle in the Z-isomer [61]. As was mentioned above, the contribution of the

Photoinduced in situ generation of DNA-targeting ligands: DNA-binding and DNA-photodamaging properties of benzo[c]quinolizinium ions

• Julika Schlosser,
• Olga Fedorova,
• Yuri Fedorov and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 101–117, doi:10.3762/bjoc.20.11

• formation of different intermediates in the reaction sequence starting with E–Z isomerization, followed by photocyclization and subsequent oxidation. In general, the photoreaction was more efficient in polar, protic aqueous solvents (cf. Supporting Information File 1, Figures S2B–S6B) or in buffer solution

Effects of the aldehyde-derived ring substituent on the properties of two new bioinspired trimethoxybenzoylhydrazones: methyl vs nitro groups

• Dayanne Martins,
• Roberta Lamosa,
• Talis Uelisson da Silva,
• Carolina B. P. Ligiero,
• Sérgio de Paula Machado,
• Daphne S. Cukierman and
• Nicolás A. Rey

Beilstein J. Org. Chem. 2023, 19, 1713–1727, doi:10.3762/bjoc.19.125

• ability to undergo E/Z isomerization in a stimuli-responsive imine bond is what makes this class useful for applications in the field of molecular electronics, as switchers [5][6]. In addition, these compounds can also adopt syn- or antiperiplanar conformations, due to the constriction of the rotation

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• undergoing reductive elimination to afford to [2 + 2] adduct, β-oxygen elimination followed by E/Z isomerization and intramolecular lactonization generates the annulated coumarin scaffold. In 2003, the Cheng lab extended on this Ni-catalyzed ring-opening strategy [31]. It was noted the addition of 1.5

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

• chloride-mediated iminium E–Z isomerization may take place through the intermediacy of α-chloroamide 21. The aza-Nazarov reaction of the more stable E-iminium ion 20b is expected to proceed faster due to steric considerations giving the major diastereomer 19 whereas the less stable Z-iminium ion 20a would

• provide the minor diastereomer 22. In the case of aza-Nazarov reactions of 3,4-dihydroisoquinoline derivatives, an E–Z isomerization of the iminium intermediates is not possible due to their cyclic nature, which leads to the formation of the aza-Nazarov products as single diastereomers. The aza-Nazarov

• -Nazarov product 7b, albeit in a lower yield (24%). The fact that the other diastereomer of the aza-Nazarov product 7b, which would be formed via the reaction of acyl chloride 6bb with (Z)-olefin configuration, was not observed in this transformation points to a potential E–Z isomerization during the

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

• to unsubstituted diazocines 10c and 11c. The activation barrier (EA) of the E→Z isomerization (obtained by an Arrhenius plot) is higher in formylated compounds 11 compared to acetylated compounds 10 and is further increased by halogenation. The unsubstituted N-formyl diazocine 11c and brominated NAc

Vicinal difluorination as a C=C surrogate: an analog of piperine with enhanced solubility, photostability, and acetylcholinesterase inhibitory activity

• Yuvixza Lizarme-Salas,
• Alexandra Daryl Ariawan,
• Ranjala Ratnayake,
• Hendrik Luesch,
• Angela Finch and
• Luke Hunter

Beilstein J. Org. Chem. 2020, 16, 2663–2670, doi:10.3762/bjoc.16.216

• to undergo facile E/Z isomerization upon the absorption of UV photons, leading rapidly to a mixture of all four possible geometric isomers of 1 [15][16][17]. In the present work, this phenomenon was confirmed by exposing an ethanolic solution of 1 to sunlight for 2.5 h (Figure 3). The analysis of the

Starazo triple switches – synthesis of unsymmetrical 1,3,5-tris(arylazo)benzenes

• Andreas H. Heindl and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2020, 16, 22–31, doi:10.3762/bjoc.16.4

• switchable multistate photoswitches: previous [11][12] and present work. a) UV–vis spectra of tris(arylazo)benzenes 3a/3b in ethanol. b) Reversible photoisomerization of 3a and c) 3b using light of 365 nm wavelength to induce E→Z isomerization and of 448 nm wavelength for photochemical back-conversion

Design, synthesis and investigation of water-soluble hemi-indigo photoswitches for bioapplications

• Daria V. Berdnikova

Beilstein J. Org. Chem. 2019, 15, 2822–2829, doi:10.3762/bjoc.15.275

• this case, the backward E–Z isomerization of E-1c from PSS470 took place within 5 h resulting in almost complete restoration of the initial absorbance of Z-1c in the PSS590 (Figure 1C). Investigation of the photostationary mixtures by fluorescence spectroscopy revealed that the photoinduced isomers E

• responsible for the rate of thermal E–Z isomerization pointing out the importance of the Coulomb interactions between hemi-indigo and buffer components. A possible explanation of this observation can be provided by the comparison with structurally related hemi(thio)indigo dyes [22]. Thus, in the case of hemi

A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

• Constantin Stuckhardt,
• Diederik Roke,
• Wojciech Danowski,
• Edwin Otten,
• Sander J. Wezenberg and
• Ben L. Feringa

Beilstein J. Org. Chem. 2019, 15, 2767–2773, doi:10.3762/bjoc.15.268

• THI of this isomer. Conversion of cage Pd2(stable E-1)4 to Pd2(unstable Z-1)4 by photochemical E/Z isomerization of ligand stable E-1 to unstable Z-1 was performed by irradiation of a sample of Pd2(stable E-1)4 at 312 nm at −20 °C (Figure 5iv). Signals of cage Pd2(stable Z-1)4 disappeared and the

• experiments highlight the reversible formation of Pd2(unstable Z-1)4 through photochemical E/Z isomerization of the ligands. On the other hand, allowing the THI of ligands unstable Z-1 in cage Pd2(unstable Z-1)4 to take place by leaving the solution at room temperature for 5 d did not lead to the formation of

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

• guest molecules inside the cage was demonstrated independently by NMR spectroscopy and single-crystal X-ray diffraction. Exposure to UV light resulted in an E→Z isomerization of the guest, which was accompanied by the expulsion of one of two guest molecules from the cage. Different from the previously

Azologization and repurposing of a hetero-stilbene-based kinase inhibitor: towards the design of photoswitchable sirtuin inhibitors

• Christoph W. Grathwol,
• Nathalie Wössner,
• Sören Swyter,
• Adam C. Smith,
• Enrico Tapavicza,
• Robert K. Hofstetter,
• Anja Bodtke,
• Manfred Jung and
• Andreas Link

Beilstein J. Org. Chem. 2019, 15, 2170–2183, doi:10.3762/bjoc.15.214

• physicochemical properties upon irradiation with light, represent one major approach to this. One of the most common light-driven transformations exploited in molecular photoswitches is the E–Z isomerization of double bonds [18]. In this context, the photochemistry of stilbenes and the closely related azobenzenes

• provided deeper insights and clarified the differential behaviour observed in the UV–vis spectra of 2b and 2f after UV irradiation. As anticipated, UV irradiation lead to E→Z isomerization of the C=C double bond in both compounds. The (Z)-isomers were found to be slightly more polar than the respective (E

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

• the double bond geometry. Since ring-closure requires the two reactive α-thienyl carbon atoms to approach each other, presumably an additional electrochemically induced E → Z isomerization occurs prior to cyclization. Indeed, there are scattered reports about configurational isomerism in stilbene

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

• dispersion forces to be a significant factor, even in the presence of hydrogen bonds. Keywords: azobenzene; hydrogen bonding; London dispersion; molecular switches; Introduction The photo-controlled E→Z isomerization of azobenzene has been known for decades [1] and has originated a wide field of

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• obtained in an E-rich form from an E/Z mixture (1:1) of the starting alkenyl phosphate, demonstrating the E/Z isomerization during the C–C-bond formation. The E/Z isomerization was also observed for the conversion of cyclododecenyl phosphate (E/Z = 9:1) to the product 3af (E/Z = 3:1). Expectedly, 4

Recent developments in the asymmetric Reformatsky-type reaction

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 325–344, doi:10.3762/bjoc.14.21

• benzoxathiazine 2,2-dioxides, as electrophiles in the catalytic enantioselective aza-Reformatky reaction [49]. Indeed, these compounds constitute good partners for asymmetric catalysis since they exhibit a rigid structure reducing the conformational mobility and avoiding the E/Z isomerization, thus facilitating

The photodecarboxylative addition of carboxylates to phthalimides as a key-step in the synthesis of biologically active 3-arylmethylene-2,3-dihydro-1H-isoindolin-1-ones

• Ommid Anamimoghadam,
• Saira Mumtaz,
• Anke Nietsch,
• Gaetano Saya,
• Cherie A. Motti,
• Jun Wang,
• Peter C. Junk,
• Ashfaq Mahmood Qureshi and
• Michael Oelgemöller

Beilstein J. Org. Chem. 2017, 13, 2833–2841, doi:10.3762/bjoc.13.275

• addition. Possible scenarios for nucleophilic cyclization to 4. Possible E/Z isomerization for compounds 8a–y. Impact of the reaction medium on the photodecarboxylative addition. Experimental results for photodecarboxylative additions. Experimental results for acid-catalyzed dehydrations. Experimental

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

Thiazol-4-one derivatives from the reaction of monosubstituted thioureas with maleimides: structures and factors determining the selectivity and tautomeric equilibrium in solution

• Alena S. Pankova,
• Pavel R. Golubev,
• Alexander F. Khlebnikov,
• Alexander Yu. Ivanov and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2016, 12, 2563–2569, doi:10.3762/bjoc.12.251

• tautomers exist [15][18][20][21][22][23]. (E/Z)-Isomerization of the exocyclic C=N bond of the single imino form was suggested as the cause for the dynamic effect as well [24][25]. In addition, this process complicates the interpretation of NMR spectra of thiazolidines and is a likely source of

Solvent-free, visible-light photocatalytic alcohol oxidations applying an organic photocatalyst

• Martin Obst and
• Burkhard König

Beilstein J. Org. Chem. 2016, 12, 2358–2363, doi:10.3762/bjoc.12.229

• ][10][11][12]. Some derivatives were also immobilized on silica gel and applied in the oxidation of benzyl alcohols [13]. Furthermore, it was shown that the oxidation power of RFTA can be increased by coordination to scandium triflate [14]. Recently, the E/Z-isomerization of olefins with riboflavin as

On the mechanism of imine elimination from Fischer tungsten carbene complexes

• Philipp Veit,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2016, 12, 1322–1333, doi:10.3762/bjoc.12.125

• ligand [Fc-C=N-Fc]– (15–) as further alternative (pathway 3c, Scheme 4). The calculated Gibbs free energies for W(CO)5(E-2) and W(CO)5(Z-2) are basically identical (Supporting Information File 1, Figure S16, Scheme 3). The calculated barrier for the E/Z isomerization W(CO)5(E-2) → W(CO)5(Z-2) amounts to

• (carbene)–N moiety. This reaction coordinate is fully analogous to the proposed mechanism of the E/Z isomerization of imines [66][67]. During the 1,2-H-shift of E-2 to E-3, the migrating hydrogen atom interacts with the empty pπ-type orbital of the carbene carbon atom (ΔG‡ = 250 kJ mol−1), which is in

• with the hydrogen 1s orbital. Because of the non-crossing rule, this path is symmetry forbidden for aromatic carbenes [47][72]. The calculated barrier of the E/Z isomerization Z-3 → E-3 (ΔG‡ = 52 kJ mol−1) is in good agreement with experimental data for other imines with similar steric bulk, e.g., (Fc

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

• Laura A. Bryant,
• Rossana Fanelli and
• Alexander J. A. Cobb

Beilstein J. Org. Chem. 2016, 12, 429–443, doi:10.3762/bjoc.12.46

• utilized a 9-OH benzoyl derivatised cupreine CPN-38 to effect a Friedel-Crafts reaction of 2-naphthols 36 with benzoxathiazine 2,2-dioxides 37 (Scheme 10). These cyclic imides, derived from salicylic aldehydes, have a rigid structure which prevents E/Z-isomerization, allowing for greater control over the

Synthesis of photoresponsive cholesterol-based azobenzene organogels: dependence on different spacer lengths

• Yuchun Ren,
• Bin Wang and
• Xiuqing Zhang

Beilstein J. Org. Chem. 2015, 11, 1089–1095, doi:10.3762/bjoc.11.122

• can bring about new predictable gelation abilities for the construction of novel cholesterol-based gelators. Azobenzene is one of the smartest molecules among all known photochromic compounds because of its E/Z isomerization [18]. Based on this, photomechanical soft materials containing azobenzene