Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• alkene 307 (e.g., protected allylic alcohols) was explored by varying the ligand on copper. Using catalytic CuCl/Xantphos, direct access to anti-Markovnikov alkylborated products (e.g., 353, 354) was noted. Alternatively, simply switching from Xantphos to Cy-Xantphos afforded the products of Markovnikov

• conversion of 2-substituted 1,3-dienes 376 into borocyano products using commercially available phosphine ligands (Scheme 60). Simply switching from a mono to a bidentate ligand resulted in 1,4 to 4,1-borocupration. The formation of allyl–Cu intermediates in the catalytic cycle readily trap available

Cascade trifluoromethylthiolation and cyclization of N-[(3-aryl)propioloyl]indoles

• Ming-Xi Bi,
• Shuai Liu,
• Yangen Huang,
• Xiu-Hua Xu and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2020, 16, 657–662, doi:10.3762/bjoc.16.62

• slightly higher yields, respectively (Table 1, entries 3 and 4). Switching KHCO3 to NaHCO3 could enhance the yield (Table 1, entry 6), whereas K2CO3 and DBU reduced the reaction efficiency (Table 1, entries 5 and 7). Subsequent evaluation of solvents revealed that MeCN and DMF were inferior to DMSO (Table

Synthesis of 4-amino-5-fluoropyrimidines and 5-amino-4-fluoropyrazoles from a β-fluoroenolate salt

• Tobias Lucas,
• Jule-Philipp Dietz and
• Till Opatz

Beilstein J. Org. Chem. 2020, 16, 445–450, doi:10.3762/bjoc.16.41

• investigate the use of non-nucleophilic bases, but with DBU, polymerization of the fluoroenolate took place. When using aqueous sodium hydroxide as the base, a 19% yield could be achieved. Switching the solvent to water led to an improvement of the yield to 36% (Table 2). In water, but without using a base

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• is more than 80–95% depending on substitution. Thus, such absorbers can also work in systems where typically thermal processes initiated by furnace techniques play the major role. These absorbers generate heat on demand just by switching on and off the light source. Thus, they can be seen more or

• intensity (<100 mW/cm2) NIR-LED resulting in radicals and conjugate acid [5]. Most of them comprised a barbiturate group. 26, 34, 47, and 48 depict some representative examples. On the other hand, positively charged sensitizers showed no reactivity with such a low intensity LED [5]. Switching the LED source

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• . The π-acceptor character of phosphorus can be reinforced by the presence of oxygen and/or nitrogen whilst σ-donating potency of nitrogen can be manipulated by switching between sp3 and sp2 hybridization [9][49][50]. The synthesis of phosphines is quite delicate because when exposed to air, some of

Formal preparation of regioregular and alternating thiophene–thiophene copolymers bearing different substituents

• Atsunori Mori,
• Keisuke Fujita,
• Chihiro Kubota,
• Toyoko Suzuki,
• Kentaro Okano,
• Takuya Matsumoto,
• Takashi Nishino and
• Masaki Horie

Beilstein J. Org. Chem. 2020, 16, 317–324, doi:10.3762/bjoc.16.31

• groups, was obtained with a slightly low molecular weight, suggesting improved solubility compared to 6a (R2 = Me and R1 = n-hexyl), the attempted dissolution of the obtained polythiophene 6b in chloroform was unsuccessful. Switching the oligosiloxane moiety to a branched derivative (R2 = (CH2)4Si(Me

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• photoswitching (λ = 450 nm for Z → E and 530 nm for E → Z switching), with the high fatigue resistance characteristic of HTIs. The E-isomer's thermal half-life in EtOAc or DMSO was ca. 40 s (Figure 3 and Supporting Information File 1, Figure S3). Its absorption spectra and photoswitchability were unaltered by

• ) with enhanced proportions of E-isomer can be photogenerated would represent an exciting advance: they could, in contrast to the other photoswitch types, allow all-visible, photoreversible, high-potency switching while reproducing similarly beneficial photoswitchability of bioactivity. Mechanistic

• , respectively. c) Photoreversible switching upon alternating illumination (λ = 450 and 530 nm). d) Thermal relaxation at room temperature after reaching the photostationary state at λ = 450 nm. a) Resazurin reduction assay for HITub-4 and nocodazole in HeLa cells (n = 3), demonstrating the difference in

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• switching of binding properties [36]. Apparently, styryl-substituted aromatic derivatives could fill this gap because the [2 + 2] photocyclization reaction of stilbenes and derivatives thereof is a well-established reversible photoreaction [37][38][39][40][41][42][43][44][45][46], and styryl dyes, in

• (black), 0.04 (red), 0.08 (blue), and 2.0 (green). A) Photometric and B) CD spectroscopic monitoring of the photoinduced switching (4b: λex = 315 nm, 3b: λex = 450 nm) between 4b (c = 20 µM, black) and 3b (red) in the presence of ct DNA (c = 20 µM) in BPE buffer. DNA concentration in base pairs

• . Synthesis of styrylquinolizinium derivatives 3a–d. Possible pathways for the selective photodimerization of styrylquinolizinium derivatives 3b and 3c. Photoinduced switching of the DNA binding properties of styrylquinolizinium compound 3b. Absorption and emission data for styrylquinolizinium derivatives 3a

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

• Sabrina Müller,
• Jannik Paulus,
• Jochen Mattay,
• Heiko Ihmels,
• Veronica I. Dodero and
• Norbert Sewald

Beilstein J. Org. Chem. 2020, 16, 60–70, doi:10.3762/bjoc.16.8

• as a result of the switching process. The amide proton of the azobenzene moiety at 8.7 ppm and the adjacent methylene group at 4.5 ppm met these requirements, and hence were used for analysis (Figure 1). The proportions of the individual species in the mixture were determined by integration 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

• characterized in terms of their isomerization behavior using UV–vis and 1H NMR spectroscopy. The efficient synthesis of this new class of unsymmetrical tris(arylazo)benzenes opened new avenues to novel multistate switching materials. Keywords: multistate photoswitches; synthesis; tris(arylazo)benzene

• their isomerization properties [3][4]. Also, the incorporation of AB units into cyclic [5] or macrocyclic structures can control the switching, depending, i.a., on symmetry and ring strain [6][7][8][9]. By combining these approaches, half-lives can be tuned from milliseconds to years. The incorporation

• properties of such compounds have not been studied yet. Going one step further, this type of compounds could be substituted in an unsymmetrical way with different azo units, which allowed individual switching using light of different wavelengths [12]. These compounds were then investigated theoretically by

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

• beyond 3000 years have been achieved [14]. Unlike most of the widely applied photochromes (spiropyrans, spirooxazines, chromenes, dithienylethenes, etc.), both forms of hemi-indigo absorb in the visible light region. Therefore, photochemical switching does not require the use of the UV light, which is of

• systems, photoswitching of these compounds was tested in aqueous medium (Scheme 3). The forward reaction was performed upon irradiation at 360 (UV), 420 nm (violet), 470 nm (blue) and 520 nm (green) light (Figure 1 and Figures S1 and S2 in Supporting Information File 1). Surprisingly, almost no switching

• extent depends on the particular sequence of RNA. Photoswitching of the RNA-bound hemi-indigo Z-2 to the E-form results in emission quenching. The ON–OFF fluorescence switching of Z-2–RNA complexes can be performed reversibly by repeated irradiation with blue (470 nm) and amber (590 nm) light. Conclusion

Chemical tuning of photoswitchable azobenzenes: a photopharmacological case study using nicotinic transmission

• Lorenzo Sansalone,
• Jun Zhao,
• Matthew T. Richers and
• Graham C. R. Ellis-Davies

Beilstein J. Org. Chem. 2019, 15, 2812–2821, doi:10.3762/bjoc.15.274

• properties of the tetrafluoroazobenzene (4FAB) scaffold. Ultraviolet light switching and rapid thermal relaxation of the metastable cis configuration are the main drawbacks associated with standard AB-based switches. We designed our photoprobes to take advantage of the excellent thermodynamic stability of

Photoreversible stretching of a BAPTA chelator marshalling Ca²⁺-binding in aqueous media

• Aurélien Ducrot,
• Arnaud Tron,
• Robin Bofinger,
• Ingrid Sanz Beguer,
• Jean-Luc Pozzo and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2019, 15, 2801–2811, doi:10.3762/bjoc.15.273

• integrating a spiroamidorhodamine with a BAPTA, whose anticipated switching remains to be proven [27]. Further, interesting approaches are currently being developed on interfacing calmodulin, a messenger protein ionophore, with photochromes [28]. The use of steric effects to decrease binding offers an

• electron-transfer reaction, while ion binding blocks this quenching pathway restoring emission. Thus, ion liberation from 1 and transfer to 3 would result in a fluorescence off–on switching of the latter. To perform the ion-transfer experiment, the fluorescent dye is loaded with one equivalent of Ca2

• switching in terms of quantum yields (0.08) and PSS composition (88% cis). The calcium binding affinity of the cis-form was diminished by circa 2.5-fold with respect to the trans-form as the chelator was stretched rendering the binding pocket ill-adapted to accommodate the calcium, as suggested by molecular

An improved, scalable synthesis of Notum inhibitor LP-922056 using 1-chloro-1,2-benziodoxol-3-one as a superior electrophilic chlorinating agent

• Nicky J. Willis,
• Elliott D. Bayle,
• George Papageorgiou,
• David Steadman,
• Benjamin N. Atkinson,
• William Mahy and
• Paul V. Fish

Beilstein J. Org. Chem. 2019, 15, 2790–2797, doi:10.3762/bjoc.15.271

• efficient step in our sequence and justified further optimisation (vide infra). Suzuki–Miyaura cross coupling of bromide 5 with cyclopropylboronic acid (2.5 equiv) produced 6 in good yield (62–89%) but the product required extensive chromatographic purification. We reasoned that switching from the boronic

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

• interesting strategy to form responsive coordination complexes, as they feature a large geometric change upon switching [47]. Herein, we report a photoresponsive coordination cage with ligands based on a first generation molecular motor (Figure 1). Cages with a Pd2L4 composition are formed from bidentate

• explanation could be that the mixture of stable Z-1 and stable E-1 does not form separate well-defined cage structures, but forms mixed complexes. Conclusion In summary, a new photoresponsive supramolecular coordination complex based on overcrowded alkenes is presented, allowing switching between three

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• ] is accompanied by large variations in their absorption spectra. However, azobenzenes remain one of the most popular photoswitches owing to their stability, reliability and tunability: azobenzenes provide high extinction coefficients and quantum yields, allowing switching between Z- and E-isomers with

• low-intensity light, and are stable to repeated switching cycles. Of the several performance metrics that can be used to judge azo switches, however, there are two predominant ones that can prove problematic for azoarenes: 1) the completeness of switching at a given wavelength of light, and 2) the

• -life (t1/2 = 74 days at 25 °C). The photochemical addressability of the azopyrazoles can further be complemented by other stimuli, for example chemical switching using acid [19]. Given their excellent performance, arylazopyrazoles are replacing azobenzenes in optically addressable applications

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• (Figure 1) [25][27]. Switching of such diarylethene dyes in both directions (ring closure/coloration or ring opening/discoloration) by UCNPs has been documented for years, with a seminal work reported in 2009 by the team of Branda [28]. In the following we will show how this photochromic compound can be

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• these dyes such as intramolecular charge-transfer processes and tunable red-shifted emission bands. Generally, the so far investigated borylated arylisoquinoline dyes show principally fluorescence quenching (on-off switching) on the formation of the corresponding fluoroboronate complexes [37]. Herein

A new approach to silicon rhodamines by Suzuki–Miyaura coupling – scope and limitations

• Thines Kanagasundaram,
• Antje Timmermann,
• Carsten S. Kramer and
• Klaus Kopka

Beilstein J. Org. Chem. 2019, 15, 2569–2576, doi:10.3762/bjoc.15.250

• internal salt (protonated pyridine ring and deprotonated boronic acid) and ensuing difficult formation of boroxine 29b (Table 2, entry 10). Switching to the neutral heterocyclic boronic acid 30a, the corresponding thienyl-substituted silicon rhodamine 30c could be obtained in 37% (56% brsm) yield with the

A toolbox of molecular photoswitches to modulate the CXCR3 chemokine receptor with light

• Xavier Gómez-Santacana,
• Sabrina M. de Munnik,
• Tamara A. M. Mocking,
• Niels J. Hauwert,
• Shanliang Sun,
• Prashanna Vijayachandran,
• Iwan J. P. de Esch,
• Henry F. Vischer,
• Maikel Wijtmans and
• Rob Leurs

Beilstein J. Org. Chem. 2019, 15, 2509–2523, doi:10.3762/bjoc.15.244

• also activate the receptor to varying degrees. In all, our efforts deliver a spectrum of (subtle) efficacy differences. Notable tool compounds are VUF15888 (4d) switching from antagonism to partial agonism (PDE = 0.43), VUF16620 (6e) switching from partial agonism to full agonism (PDE = 0.51), and

In search of visible-light photoresponsive peptide nucleic acids (PNAs) for reversible control of DNA hybridization

• Lei Zhang,
• Greta Linden and
• Olalla Vázquez

Beilstein J. Org. Chem. 2019, 15, 2500–2508, doi:10.3762/bjoc.15.243

• switching capacities and duplex formation were analyzed. Our group has recently demonstrated that photoresponsive peptides can affect the transcription of genes via inhibition of histone-modifying enzymes [37]. Repression of enzymes is achievable at nucleic acid level too. Therefore, in this project we

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• stimulus, raise particular interest among the different classes of switches which have been developed to date. Light enables very specific spatial and temporal control of the switching event, allowing for selective response and bidirectional operation. It is thus not surprising that different classes of

• patterns, yielding systems that absorb in the red part of the visible spectrum [28]. Recently, a new hydrazone-based photochromic compound, exhibiting outstanding properties, has been synthetized and characterized [29]. This molecule presents fluorescence ON/OFF switching under both one-photon and two

• , fluorescence toggling and two-photon induced switching. Using a combination of time-resolved fluorescence and transient absorption spectroscopies we were able to gain new insights into the isomerization process of this molecule. Time-resolved luminescence measurements allowed us to determine the excited state

Effect of ring size on photoisomerization properties of stiff stilbene macrocycles

• Sandra Olsson,
• Óscar Benito Pérez,
• Magnus Blom and
• Adolf Gogoll

Beilstein J. Org. Chem. 2019, 15, 2408–2418, doi:10.3762/bjoc.15.233

• ][9][10][11]. The interplay between the forces involved in the switching action and the pull from groups attached to the stiff stilbene has been investigated, e.g., as molecular force probes [12][13][14][15][16][17][18]. While these do incorporate other isomerizable units in addition to stiff stilbene

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

• switching to the Z isomer was accompanied by the release of one of the two guests from the cage and the formation of a 1:1 cage/Z-arylazopyrazole inclusion complex. DFT calculations suggest that this process involves a dramatic change in the conformation of the cage. Back-isomerization was induced with

• ] and, using larger cages, the synthesis of 4 nm silica nanoparticles, which would be difficult to obtain otherwise [15]. One class of organic compounds that exhibit various intriguing properties under confinement is photochromic molecules. In a seminal contribution, unusual switching patterns have been

• ), the signal due to H1 shifted upfield by 0.20 ppm. This behavior is analogous to our previous findings, which showed that shifts of H1 protons are indicative of switching of the bound guest and/or (de)encapsulation [18][49]. Integrating the signals due to E-1’s Hc protons (cyan in Figure 6) allowed us

Targeted photoswitchable imaging of intracellular glutathione by a photochromic glycosheet sensor

• Xianzhi Chai,
• Hai-Hao Han,
• Yi Zang,
• Jia Li,
• Xiao-Peng He,
• Junji Zhang and
• He Tian

Beilstein J. Org. Chem. 2019, 15, 2380–2389, doi:10.3762/bjoc.15.230

• emission fatigue resistance was also examined and found to tolerate more than five switching cycles in PBS buffer (Figure 1D). Similar performances were also observed for control reporter 8o (Supporting Information File 1, Figure S1). The characteristic photoswitchable ON/OFF fluorescence signals as well

• intensity at 535 nm performed an ON/OFF switching cycle upon irradiation of UV–vis light with a decent fatigue resistance (Figure 3D), which is in good accordance with the results of Glyco-DTE in buffer solution. The selectivity of Glyco-DTE@MnO2 towards other intracellular species was next tested by

• (3 min) with a reaction constant of k = 2.39 × 10−2 s−1 (Supporting Information File 1, Figure S3D), demonstrating a fast response of the hybrid sensor on GSH sensing. The investigation above verifies that the photochromic glycosheet we designed can perform as an “activation and photo-switching