Regioselective alkylation of a versatile indazole: Electrophile scope and mechanistic insights from density functional theory calculations

• Pengcheng Lu,
• Luis Juarez,
• Paul A. Wiget,
• Weihe Zhang,
• Krishnan Raman and
• Pravin L. Kotian

Beilstein J. Org. Chem. 2024, 20, 1940–1954, doi:10.3762/bjoc.20.170

• ethyl acetate in hexane from 0–60%) to give methyl 5-bromo-2-alkyl-2H-indazole-3-carboxylate in 90–97% yield. For 16a, 291 mg, 92%, as a light pink solid. Mp 110.7 °C; 1H NMR (300 MHz, DMSO-d6) δ 8.14 (d, J = 2.0 Hz, 1H), 7.77 (dd, J = 9.1, 0.7 Hz, 1H), 7.49 (dd, J = 9.0, 1.9 Hz, 1H), 4.42 (s, 3H), 3.98

Negishi-coupling-enabled synthesis of α-heteroaryl-α-amino acid building blocks for DNA-encoded chemical library applications

• Matteo Gasparetto,
• Balázs Fődi and
• Gellért Sipos

Beilstein J. Org. Chem. 2024, 20, 1922–1932, doi:10.3762/bjoc.20.168

• Negishi reaction (Supporting Information File 1). Preliminary experiments were carried out with and without blue light irradiation in the PhotoCubeTM photoreactor [45]. These experiments revealed that while the conversion of imidazoles and pyrazoles benefits from irradiation, thiazoles seem to be largely

• unaffected by the presence of light (see pages 5 and 6 in Supporting Information File 1). In the case of indazoles, increased reaction rates were observed in the presence of light, but the overall yield was the same for the dark and irradiated experiments. Although these reactions are typically complete

• within 4 h in the dark, irradiation with blue light halves the reaction time for many compounds. Overall, these observations are in line with those of Alcazar et al. [43]. In their work, the authors demonstrated the formation of a complex between palladium and the organozinc reagent which is absorbing in

Novel oxidative routes to N-arylpyridoindazolium salts

• Oleg A. Levitskiy,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2024, 20, 1906–1913, doi:10.3762/bjoc.20.166

• has been confirmed by the experimental results given in Scheme 2 above. Comparison of the CV curves measured for N-arylpyridoindazolium salts S1–S3 and their precursors – the diarylamines – sheds light of the nature of the electrochemical process. In Figure 1a, it is shown for salt S2. If the

A facile three-component route to powerful 5-aryldeazaalloxazine photocatalysts

• Ivana Weisheitelová,
• Radek Cibulka,
• Marek Sikorski and
• Tetiana Pavlovska

Beilstein J. Org. Chem. 2024, 20, 1831–1838, doi:10.3762/bjoc.20.161

• has been successfully applied as photoredox catalyst in the synthesis of secondary or primary anilines via light-dependent desulfonylation or desulfonylation/dealkylation procedures [19]. Thus, the design of novel and efficient routes for the synthesis of 5-aryldeazaalloxazines 2 has become a

• /alloxazine photoredox catalysis [9][14][15][16][17][18][19], 7-methoxyderivatives should also be considered due to their absorption closer to the visible light region. This allows longer wavelength LEDs with lower energy photons to be applied, potentially contributing to avoiding undesired reactions [14][15

• potent, biologically active compounds. Interestingly, the introduction of a strong methoxy group at position 7 of the 5-aryldeazaalloxazine core led to a bathochromic shift in the absorption spectra of the synthesised molecules, making them more suitable for visible light photocatalysis. Experimental

Hetero-polycyclic aromatic systems: A data-driven investigation of structure–property relationships

• Sabyasachi Chakraborty,
• Eduardo Mayo Yanes and
• Renana Gershoni-Poranne

Beilstein J. Org. Chem. 2024, 20, 1817–1830, doi:10.3762/bjoc.20.160

• molecules have been used in diverse settings, functioning as organic field effect transistors [10][11][12], light-emitting diodes [13][14][15], organic semiconductors [16][17], organic photovoltaics [1][18][19][20][21][22], photocatalysts [23], and biological agents for tracking or inhibition [24][25], and

• nature on the molecular properties of PASs. Our goal is to delineate specific structure–property relationships that may shed light on these prevalent, yet still mysterious, compounds and serve as design principles for future PASs. Data The molecules in COMPAS-2 contain 11 cyclic building blocks varying

• distribution of the COMPAS-1 molecules (light blue) is contained within the distribution of the COMPAS-2 molecules (purple). In other words, the expansion of the building block library widens the property distributions towards both higher and lower energies, providing access to functional molecules with

Synthesis and characterization of 1,2,3,4-naphthalene and anthracene diimides

• Adam D. Bass,
• Daniela Castellanos,
• Xavier A. Calicdan and
• Dennis D. Cao

Beilstein J. Org. Chem. 2024, 20, 1767–1772, doi:10.3762/bjoc.20.155

• title compounds indicates that they are optically and electronically similar to previously reported naphthalene and anthracene diimides, absorbing/emitting light in the visible region and readily undergoing one-electron-reduction processes. As such, this work opens the possibility of incorporating the

Synthesis of polycyclic aromatic quinones by continuous flow electrochemical oxidation: anodic methoxylation of polycyclic aromatic phenols (PAPs)

• Hiwot M. Tiruye,
• Solon Economopoulos and
• Kåre B. Jørgensen

Beilstein J. Org. Chem. 2024, 20, 1746–1757, doi:10.3762/bjoc.20.153

• estitmation of the HOMO/LUMO energies to shed more light on this transformation. The easy separation of the supporting electrolyte from the product will allow recycling and makes this a green transformation. Keywords: acetal formation; cyclic voltammetry; flow electrochemistry; green oxidation; polycyclic

Chemo-enzymatic total synthesis: current approaches toward the integration of chemical and enzymatic transformations

• Ryo Tanifuji and
• Hiroki Oguri

Beilstein J. Org. Chem. 2024, 20, 1693–1712, doi:10.3762/bjoc.20.151

• fractionated cell cultures of M. alba with 49 was followed by irradiation with 365 nm light to generate reactive carbene from diazirine. This sequence allowed the formation of covalent bonds between the synthetic probe and binding proteins. The resulting mixture was subjected to a copper-catalyzed click

A fiber-optic spectroscopic setup for isomerization quantum yield determination

• Anouk Volker,
• Jorn D. Steen and
• Stefano Crespi

Beilstein J. Org. Chem. 2024, 20, 1684–1692, doi:10.3762/bjoc.20.150

• actinometry, thus demonstrating the reliability of our setup. Keywords: isomerization; molecular photoswitches; photochemistry; photon flux; UV–vis spectroscopy; Introduction Photoswitches are molecules that can undergo a light-driven structural rearrangement to populate a metastable state of the initial

• reactant. This isomerization can be reversed by light of a different wavelength or thermal stimuli. Depending on the nature of the reactant, different classes of photoreactions can be utilized: double bond isomerizations, electrocyclization, cycloadditions, and electron-, hydrogen-, or group transfer [1

• . [17], the spectrum of trans-azobenzene can be easily obtained by careful preparation of the sample in the dark. The absorption spectrum of cis-azobenzene, however, is challenging to obtain via direct measurement, due to its intrinsic thermal instability and sensitivity to ambient light. The authors

Ring opening of photogenerated azetidinols as a strategy for the synthesis of aminodioxolanes

• Henning Maag,
• Daniel J. Lemcke and
• Johannes M. Wahl

Beilstein J. Org. Chem. 2024, 20, 1671–1676, doi:10.3762/bjoc.20.148

• strategy is founded on the build and release of molecular strain and achieves a formal transposition of a methyl group. During light irradiation, 3-phenylazetidinols are forged as reaction intermediates, which readily undergo ring opening upon the addition of electron-deficient ketones or boronic acids

Polymer degrading marine Microbulbifer bacteria: an un(der)utilized source of chemical and biocatalytic novelty

• Weimao Zhong and
• Vinayak Agarwal

Beilstein J. Org. Chem. 2024, 20, 1635–1651, doi:10.3762/bjoc.20.146

• electron transport in the photosynthetic light reactions by interfering with the synthesis of plastoquinone-9 [17]. Global genome sequence analyses confirmed the ubiquitous presence of biosynthetic gene clusters (BGCs) encoding the production of 26 in diverse marine bacterial species, suggesting it to be a

New triazinephosphonate dopants for Nafion proton exchange membranes (PEM)

• Fátima C. Teixeira,
• António P. S. Teixeira and
• C. M. Rangel

Beilstein J. Org. Chem. 2024, 20, 1623–1634, doi:10.3762/bjoc.20.145

• combinatorial chemistry [35], in analytical chemistry, in electrochemical redox processes, in crystal engineering, and as fluorescent, light emitting, corrosion inhibitors or several other materials [36][37][38][39][40][41][42]. The most used triazine is 1,3,5-triazine (or s-triazine) that can provide

Supramolecular assemblies of amphiphilic donor–acceptor Stenhouse adducts as macroscopic soft scaffolds

• Ka-Lung Hung,
• Leong-Hung Cheung,
• Yikun Ren,
• Ming-Hin Chau,
• Yan-Yi Lam,
• Takashi Kajitani and
• Franco King-Chi Leung

Beilstein J. Org. Chem. 2024, 20, 1590–1603, doi:10.3762/bjoc.20.142

• UV light, we have previously reported a design of amphiphilic donor–acceptor Stenhouse adducts (DASAs) controlled by white light. Herein, we present a series of DASA amphiphiles (DAs) with minor structural modifications on the alkyl linker chain length connecting the DASA motif with the hydrophilic

• moiety. The excellent photoswitchability in organic medium and the photoresponsiveness in aqueous medium, driven by visible light, were investigated by UV–vis absorption spectroscopy. The assembled supramolecular nanostructures were confirmed by electron microscopy, while the supramolecular packing was

• revealed by X-ray diffraction analysis. Upon visible-light irradiation, significant transformations of the DA geometry enabled transformations of the supramolecular assemblies on a microscopic scale, subsequently disassembling macroscopic soft scaffolds of DAs. The current work shows promising use for the

Divergent role of PIDA and PIFA in the AlX₃ (X = Cl, Br) halogenation of 2-naphthol: a mechanistic study

• Kevin A. Juárez-Ornelas,
• Manuel Solís-Hernández,
• Pedro Navarro-Santos,
• J. Oscar C. Jiménez-Halla and
• César R. Solorio-Alvarado

Beilstein J. Org. Chem. 2024, 20, 1580–1589, doi:10.3762/bjoc.20.141

• mixing PIDA with aluminum bromide, the reaction occurred with an unexpectedly higher yield (93%) than with PIFA. Therefore, the bromination reaction proceeded in the presence of PIDA/AlBr3 as a brominating system using MeCN as solvent (Scheme 3). In light of the relevance of this newly discovered

Benzylic C(sp³)–H fluorination

• Alexander P. Atkins,
• Alice C. Dean and
• Alastair J. J. Lennox

Beilstein J. Org. Chem. 2024, 20, 1527–1547, doi:10.3762/bjoc.20.137

• functionalisation of benzylic C–H bonds to benzylic radicals can be envisaged to occur through three different pathways (Figure 22). Upon excitation by light, photoredox reagents can induce a number of changes in benzylic substrate I, either directly or via mediated processes. Hydrogen-atom-transfer (HAT) results

• pioneering report in 2013 that used photocatalyst 9-fluorenone under visible-light irradiation to generate a photoexcited aryl ketone, capable of HAT to promote benzylic fluorination with Selectfluor (Figure 23) [69]. The reaction tolerated an exceptional range of functional groups and enabled the

• showed that 1,2,4,5-tetracyanobenzene could be used under ultraviolet light irradiation as a photocatalyst in the fluorination of benzylic C(sp3)–H bonds (Figure 25) [70]. Selectfluor was used as the FAT reagent to furnish a selection of primary, secondary and tertiary benzyl fluorides with different

Electrophotochemical metal-catalyzed synthesis of alkylnitriles from simple aliphatic carboxylic acids

• Yukang Wang,
• Yan Yao and
• Niankai Fu

Beilstein J. Org. Chem. 2024, 20, 1497–1503, doi:10.3762/bjoc.20.133

• esters, the so called "Barton esters", for decarboxylative cyanation of aliphatic acids with tosyl cyanide as the nitrile source under visible light irradiation at room temperature [21][22]. Although two synthetic steps are required, this is the first practical decarboxylative cyanation protocol because

• by anodic oxidation and visible light irradiation of the Ce species in a sequential fashion [38][39][40][41][42][43][44][45]. Therefore, the anodic electrode potential for this process could be substantially reduced. In doing so, a low working potential at the anode offers the opportunity for

• plate as the cathode, was electrolyzed with a cell potential of 2.3 V (corresponding to an initial anodic potential of 0.10 V versus the ferrocenium ion/ferrocene redox couple) under the irradiation of 400 nm light-emitting diodes (LEDs). Through systematic optimization, we found that the use of readily

Photoswitchable glycoligands targeting Pseudomonas aeruginosa LecA

• Yu Fan,
• Ahmed El Rhaz,
• Stéphane Maisonneuve,
• Emilie Gillon,
• Maha Fatthalla,
• Franck Le Bideau,
• Guillaume Laurent,
• Samir Messaoudi,
• Anne Imberty and
• Juan Xie

Beilstein J. Org. Chem. 2024, 20, 1486–1496, doi:10.3762/bjoc.20.132

• antibiotic-sparing anti-infective drugs. Building synthetic glycoconjugates for the inhibition and modulation of bacterial lectins have shown promising results. Light-sensitive lectin ligands could allow the modulation of lectins activity with precise spatiotemporal control. Despite the potential of

• due to stronger unfavorable entropy, they are in general of lower affinity. The validation of this proof-of-concept and the dissection of thermodynamics of binding will help for the further development of lectin ligands that can be controlled by light. Keywords: carbohydrates; glycosyl azobenzenes

• photomodulating chemical, biological or pharmacological activities or properties [11][12]. Light is generally noninvasive and orthogonal toward most elements of living systems. It can be easily and precisely controlled in time, location, wavelength, and intensity, thus enabling the precise activation and

Bioinformatic prediction of the stereoselectivity of modular polyketide synthase: an update of the sequence motifs in ketoreductase domain

• Changjun Xiang,
• Shunyu Yao,
• Ruoyu Wang and
• Lihan Zhang

Beilstein J. Org. Chem. 2024, 20, 1476–1485, doi:10.3762/bjoc.20.131

• reside at the interface of domain–domain or domain–substrate interactions, shedding light on the enzyme mechanism for stereocontrol. Our work provides an overview for current bioinformatic prediction of stereoselectivity of KR in cis-AT PKS, expands the understanding of the stereocontrol of PKS from

Synthesis of 4-functionalized pyrazoles via oxidative thio- or selenocyanation mediated by PhICl₂ and NH₄SCN/KSeCN

• Jialiang Wu,
• Haofeng Shi,
• Xuemin Li,
• Jiaxin He,
• Chen Zhang,
• Fengxia Sun and
• Yunfei Du

Beilstein J. Org. Chem. 2024, 20, 1453–1461, doi:10.3762/bjoc.20.128

• presented a method for the C–H thiocyanation of pyrazoles by using a sustainable catalyst of graphite-phase carbon nitride (g-C3N4) under visible light irradiation (Scheme 1c) [2]. Furthermore, Yao harnessed an electrochemical approach to form the electrophilic SCN+ intermediate, which reacted with

A comparison of structure, bonding and non-covalent interactions of aryl halide and diarylhalonium halogen-bond donors

• Nicole Javaly,
• Theresa M. McCormick and
• David R. Stuart

Beilstein J. Org. Chem. 2024, 20, 1428–1435, doi:10.3762/bjoc.20.125

• interaction in a wide range of applications that include crystal engineering, drug discovery and light-emitting materials [1][2][3][4]. Although, halogen bonding was first “observed” over 200 years ago [5][6] and the structural characteristics were elucidated in the latter half of the nineteenth century [7

• points, in which XB donors with larger Vs,max values also had more exergonic associations, we actually observed two almost parallel clusters of data (Scheme 6c). In this case, neutral XB donors 26–28, and 30–36 had Vs,max values ≈5–50 kcal/mol and a slope of −0.24 (Scheme 6c, light grey dots), whereas

Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C–O bonds in organic transformations

• Mithu Roy,
• Bitan Sardar,
• Itu Mallick and
• Dipankar Srimani

Beilstein J. Org. Chem. 2024, 20, 1348–1375, doi:10.3762/bjoc.20.119

• radicals by activation of C–O bonds using visible-light photoredox catalysis offers a mild and environmentally benign approach to useful chemical transformations. Alcohols, carboxylic acids, anhydrides, xanthates, oxalates, N-phthalimides, and thiocarbonates are some examples of alkyl and acyl precursors

• photocatalysts, transition-metal photoredox catalysts, and metallaphotocatalysts to produce acyl and alkyl radicals driven by visible light. Keywords: acyl radical; alkyl radical; sustainable catalysis; visible light; Introduction The growing awareness of the necessity for sustainable developments has been

• synthesis [4][5][6][7][8][9]. In the context of sustainable catalysis, visible-light-mediated chemistry is becoming a prominent viable option for radical transformations in the synthesis of biologically useful compounds due to the energy efficiency and environmental friendliness [10][11]. Recently, the

Transition-metal-catalyst-free electroreductive alkene hydroarylation with aryl halides under visible-light irradiation

• Kosuke Yamamoto,
• Kazuhisa Arita,
• Masami Kuriyama and
• Osamu Onomura

Beilstein J. Org. Chem. 2024, 20, 1327–1333, doi:10.3762/bjoc.20.116

• conditions. The key to success is the use of 1,3-dicyanobenzene as a redox mediator and visible-light irradiation, which effectively suppresses the formation of simple reduction, i.e., hydrodehalogenation, products to afford the desired products in good to high yields. Mechanistic investigations proposed

• that a reductive radical-polar crossover pathway is likely to be involved in this transformation. Keywords: aryl halides; C–C bond formation; electroreduction; radicals; visible light; Introduction Alkene hydroarylation is an attractive method for the construction of alkylarenes, which serve as

• -light-mediated alkene hydroarylation commonly requires external reductants and/or hydrogen atom sources to complete the catalytic cycle [21][22][23][24][25]. Over the past few decades, electrochemistry has proven to be an environmentally benign and convenient approach for accessing open-shell

Diameter-selective extraction of single-walled carbon nanotubes by interlocking with Cu-tethered square nanobrackets

• Guoqing Cheng and
• Naoki Komatsu

Beilstein J. Org. Chem. 2024, 20, 1298–1307, doi:10.3762/bjoc.20.113

• moieties absorbing ≈465 nm light (Figure 1b) should be excited at the resonance Raman spectroscopy using a 488 nm laser. This is supported by the observation that the excitation at 633 and 785 nm where 1b did not show any absorption (Figure 1b) did not give any Raman signals [20]. Extraction of SWNTs with

• breathing vibration, resulting in higher frequency shift as shown in Figure 4 [11][26]. With normalization in G-band at 1570 cm−1, the relative intensity decreases in the RBM region of e- and i-SWNTs may be due to light absorption and/or peak broadening caused by the interlocking Cu-nanobrackets 1b

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• thorough photochemical characterization is essential for efficient light-driven applications. In this article, the mode of action of a polyazahelicene catalyst (Aza-H) was investigated using laser flash photolysis (LFP). The study revealed that the chromophore can function as a singlet-state photoredox

• (distance 6 cm) was used as the excitation light source. D) Irradiation experiments of (E)-stilbene (blue) and (Z)-stilbene (red) with 2 mol % Aza-H employing a 427 nm LED as light source. E) Schematic energy diagram of triplet sensitized E/Z isomerization of stilbene. F) Reaction scheme of the cyclization

Competing electrophilic substitution and oxidative polymerization of arylamines with selenium dioxide

• Vishnu Selladurai and
• Selvakumar Karuthapandi

Beilstein J. Org. Chem. 2024, 20, 1221–1235, doi:10.3762/bjoc.20.105

• sample vials and monitored the apparent color change (Figure S34, Supporting Information File 1). Instantaneous color change from colorless to blackish dark was observed for an o-anisidine solution after addition of SeO2. For an aniline solution, the color became light pink immediately upon addition of