Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• ), which were obtained by condensation between meso-tetrakis(4-formylphenyl)porphyrin (p-Por-CHO) and benzene-1,4-diamine, and 1,4-phenylenediacetonitrile, for Por-COF-1 and Por-COF-2, respectively (Scheme 54) [103]. The sp2 carbon-linked COF conferred high chemical stability to the material (Por-COF-2

A method to determine the correct photocatalyst concentration for photooxidation reactions conducted in continuous flow reactors

• Clemens R. Horn and
• Sylvain Gremetz

Beilstein J. Org. Chem. 2020, 16, 871–879, doi:10.3762/bjoc.16.78

• concentration, which would be required for a perfect fit between the absorption maximum and the LED emission. This highlights why it is so important to measure the absorption in the intended reaction medium. A solvent change could shift the maximum by a few nm (TPP: 416 nm in chloroform [37], 418 nm in benzene

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

• three possible dissociation pathways that can be followed (Scheme 5). Moreover, Reilly and co-workers observed the decomposition of benzaldehyde (8) into benzene (21) and carbon monoxide (22) (reaction (3) in Scheme 5) after the irradiation at 258.9 nm via laser ionization mass spectrometry and

• electronic distribution and the spectroscopy of the excited states of benzaldehyde (8) have been examined. These studies illuminate the ways that the various excited states of benzaldehyde (8) decay, either through phosphorescence or through the dissociation to benzene (21) and carbon monoxide (22) or to a

• various aldehydes and ketones that were used as photosensitizers (Scheme 15) [51]. In more detail, a solution of cis-piperylene (61) in benzene in the presence of various carbonyl compounds was irradiated using a Hanovia quartz immersion reactor. It was shown that compounds that had a triplet state energy

Towards triptycene functionalization and triptycene-linked porphyrin arrays

• Gemma M. Locke,
• Keith J. Flanagan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2020, 16, 763–777, doi:10.3762/bjoc.16.70

• candidates to study the potential electron donor–acceptor dyads [19]. Triptycene (1) consists of three benzene rings fused to a bicyclo[2.2.2]octane (BCO) skeleton, it is rigid, isolating and amenable to a wide range of chemical transformations. Due to the 120° rigid void, mono-, di-, tri-, tetra-, penta

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

• variety of substrates, although the methodology required hazardous conditions; i.e., hot benzene [62]. A few years later, similar types of reactions were carried out by Loh and co-workers [63]. In this case, a variety of α,β-unsaturated compounds, that, rather than undergoing intramolecular cyclization

Rhodium-catalyzed reductive carbonylation of aryl iodides to arylaldehydes with syngas

• Zhenghui Liu,
• Peng Wang,
• Zhenzhong Yan,
• Suqing Chen,
• Dongkun Yu,
• Xinhui Zhao and
• Tiancheng Mu

Beilstein J. Org. Chem. 2020, 16, 645–656, doi:10.3762/bjoc.16.61

• direct coupling products (namely, benzene and biphenyl) were detected as the main byproducts by GC–MS. This observation also explains why the conversions were always higher than the yields. Effects of ligands Ligands play a decisive role in adjusting the catalytic ability of metal cations [12][13][41][42

Asymmetric synthesis of CF₂-functionalized aziridines by combined strong Brønsted acid catalysis

• Xing-Fa Tan,
• Fa-Guang Zhang and
• Jun-An Ma

Beilstein J. Org. Chem. 2020, 16, 638–644, doi:10.3762/bjoc.16.60

• attributed to the increased Brønsted acidity when the strong electron-withdrawing trifluoromethyl group was placed on the benzene ring of the arylboronic acid. Removing the boronic acid from the reaction system leads to a dramatic decrease in both yield and enantiocontrol (Table 1, entry 16). The challenge

• -methoxyaniline (2a, 40.6 mg, 0.33 mmol), 2-boronobenzoic acid (COOH-BA, 3.98 mg, 0.024 mmol), anhydrous Na2SO4 (200 mg) and toluene (1 mL) at room temperature under an argon atmosphere. After reacting for 30 minutes at room temperature, ((2-diazo-1,1-difluoroethyl)sulfonyl)benzene (Ps-DFA 3, 104.5 mg, 77.4 uL

Design and synthesis of diazine-based panobinostat analogues for HDAC8 inhibition

• Sivaraman Balasubramaniam,
• Sajith Vijayan,
• Liam V. Goldman,
• Xavier A. May,
• Kyra Dodson,
• Sweta Adhikari,
• Fatima Rivas,
• Davita L. Watkins and
• Shana V. Stoddard

Beilstein J. Org. Chem. 2020, 16, 628–637, doi:10.3762/bjoc.16.59

• investigation provides a successful synthetic strategy towards four new analogues of panobinostat having diazines as the central core and details the results of their biochemical evaluation. Computational data corroborated that the substitution of benzene in the molecular framework of panobinostat for a

Synthesis of triphenylene-fused phosphole oxides via C–H functionalizations

• Md. Shafiqur Rahman and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2020, 16, 524–529, doi:10.3762/bjoc.16.48

• (trifluoroacetoxy)iodo]benzene] (PIFA) and BF3·OEt2 in dichloromethane at −78 °C afforded, after 12 h, the desired cyclized product 8a in 59% yield. The reaction could be performed on a 0.5 mmol scale in a similar yield of 58%. Note that other typical reagents used for the Scholl reaction, such as DDQ/CF3CO2H

Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

• Faïma Lazreg,
• Marie Vasseur,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2020, 16, 482–491, doi:10.3762/bjoc.16.43

• cleavage of the bond between the N-4 and C-benzene in thiadiazine ring-type molecules [9]. To date, only few examples of copper-based catalysts have been reported to enable access to such compounds [10][11][12][13]. Chang and co-workers were pioneers in this area [10][11][12]. A three-component reaction

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• photosensitizer. Because the use of polar solvents did not lead to the desired reactivity, we turned to nonpolar solvents. Since [Cu(dap)2]Cl is insoluble in nonpolar solvents, we continued with the more reducing fac-[Ir(ppy)3] photocatalyst. The choice of benzene as a solvent led to a significant formation of

• organic photocatalyst, showing hyperfine interactions with two equivalent nitrogen nuclei (giso = 2.0032; ANiso = 18.6 MHz). The HRMS of this species showed the mass of the catalyst, thus confirming that the oxidized catalyst precipitates as a salt from solution when using benzene as a solvent. Based on

• product was not formed at all. Addition of [Ag]PF6 to remove the chloride and solubilize the oxidized photocatalyst also did not lead to any product formation. [Ag]PF6 is poorly soluble in benzene and the Ag+ ion is likely to act as an oxidizing agent quenching the excited state of the photocatalyst

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

• (R = Me, iPr and Ph) in benzene produced chiral acetal 22. Subsequent palladium-catalyzed C–C coupling of the acetal with 4-fluorophenylboronic acid (FPBA) in the presence of caesium carbonate and tri-tert-butylphosphine afforded aryl fluorides 23. Pure ligands 24 (63–72%) were obtained by

Absolute configurations of talaromycones A and B, α-diversonolic ester, and aspergillusone B from endophytic Talaromyces sp. ECN211

• Ken-ichi Nakashima,
• Junko Tomida,
• Takao Hirai,
• Yoshiaki Kawamura and
• Makoto Inoue

Beilstein J. Org. Chem. 2020, 16, 290–296, doi:10.3762/bjoc.16.28

• benzene ring with a methyl group at its C-3 position. The hydrogen-bonded hydroxy group was attached to the C-1 position, as evidenced by HMBC correlations from 4-OH to C-1 (δC 160.3), C-2 (δC 112.7), and C-4a (δC 155.9), which also implied that C-9a was hydrogen-bonded to a carbonyl group. Furthermore

• carbonyl group at the C-7 position. However, the complete structure of 1 could not be determined by NMR spectroscopy due to a lack of HMBC correlations between the partial structures. Therefore, we crystalized 1 by vapor diffusion with benzene/n-hexane. Single-crystal X-ray diffraction using Cu radiation

• separated by silica gel column chromatography with n-hexane/acetone (2:1, v/v) to yield 4 (34.3 mg) and 6 (58.2 mg). Talaromycone A (1) Colorless plates (benzene/n-hexane). mp 176–179 °C; [α]D25 +18.4 (c 0.1, MeOH); 1H and 13C NMR see Table 1; UV (MeOH) λmax (log ε) 327 (3.68), 260 (4.24), 240 (4.39), 229

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• reduction potential of 1QuCN+* was higher than that of benzene (Eox vs SCE = 2.32 V), making the electron transfer from phenol to 1QuCN+* viable. The mechanistic pathway for the C–H hydroxylation of benzene derivatives is shown in Figure 19. On the other hand, Ohkubo et al. reported that substrates like

• benzene are difficult to oxidize with nonphotochemical processes, whereas with photoredox catalyst 5 and TBN in the presence of oxygen, benzene can be easily be oxidized (Scheme 19) [158]. Remarkably, photoredox catalyst 5 offered a one-step oxygenation of arenes to phenol with high quantum yields. It was

• of substituted phenols using QuCN. Synthesis of substituted phenols with DDQ (5). Aerobic bromination of arenes using an acridinium-based photocatalyst. Aerobic bromination of arenes with anthraquinone. Chlorination of benzene derivatives with Mes-Acr-MeClO4 (2). Chlorination of arenes with 4CzIPN

Synthesis and herbicidal activities of aryloxyacetic acid derivatives as HPPD inhibitors

• Man-Man Wang,
• Hao Huang,
• Lei Shu,
• Jian-Min Liu,
• Jian-Qiu Zhang,
• Yi-Le Yan and
• Da-Yong Zhang

Beilstein J. Org. Chem. 2020, 16, 233–247, doi:10.3762/bjoc.16.25

• -withdrawing and electron-donating groups were introduced onto the benzene ring of I1, which significantly influenced the HPPD inhibition activity. We found that electron-withdrawing groups improve the activity; for example, I3 (Ki = 0.36 µM) and I4 (Ki = 0.59 µM) were more potent than I1 (Ki = 1.5 µM) and I2

• , the introduction of large groups on the benzene ring appears to be beneficial to the activity and deserves further structural optimization. The herbicidal activities of compounds containing other aromatic rings, compound II and III bearing a pyridine ring and a naphthalene ring, were examined. The

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• compounds and the reference drugs. Then, the normalized PMI ratios were plotted on a triangular graph where the vertices (0,1), (0.5,0.5), and (1,1) represent a perfect rod (i.e., 2-butyne), disc (i.e., benzene), and sphere (i.e., adamantane), respectively (Figure 4). This analysis showed that all compounds

Synthesis, liquid crystalline behaviour and structure–property relationships of 1,3-bis(5-substituted-1,3,4-oxadiazol-2-yl)benzenes

• Afef Mabrouki,
• Malek Fouzai,
• Armand Soldera,
• Abdelkader Kriaa and
• Ahmed Hedhli

Beilstein J. Org. Chem. 2020, 16, 149–158, doi:10.3762/bjoc.16.17

• , University of Tunis El Manar, 2092, Tunis, Tunisia Department of Chemistry, Quebec Center for Functional Materials, University of Sherbrooke, Sherbrooke, Québec, J1K 2R1, Canada 10.3762/bjoc.16.17 Abstract Two series containing 1,3-bis(1,3,4-oxadiazol-2-yl)benzene as a rigid core (RC) and alkyl or

• characterization of two series of hydro- and fluorocarbonated 1,3-bis(1,3,4-oxadiazol-2-yl)benzenes. Structure–property relationships of the obtained compounds were investigated. Results and Discussion Synthesis When benzene-1,3-dicarbohydrazide [28] (1) was allowed to react with hydro- or perfluorocarboxylic

• et al. investigated on the liquid crystalline behaviour of some bis(phenyl-1,3,4-oxadiazolyl)benzene derivatives with varied number and length of terminal alkoxy chains [32]. The authors established that the mesogenicity is strongly enhanced in materials with four long terminal alkoxy substituents

The interaction between cucurbit[8]uril and baicalein and the effect on baicalein properties

• Xiaodong Zhang,
• Jun Xie,
• Zhiling Xu,
• Zhu Tao and
• Qianjun Zhang

Beilstein J. Org. Chem. 2020, 16, 71–77, doi:10.3762/bjoc.16.9

• had only one absorption peak. In the range of 1650–1550 cm−1 were two absorption peaks for the two benzene ring stretching vibrations of BALE and the peak disappearance observed in the inclusion complex, which may be caused by Q[8]. In addition, there were differences in the fingerprint region of the

• benzene ring. In spectrum (d), the peaks at 704, 778 and 898 cm−1 for the guest disappeared due to the inclusion of Q[8] and the molecular microenvironment of BALE being changed. From DTA (Figure 6), we can also see that BALE and Q[8] interacted with each other. Q[8] (Figure 6b) has a broad endothermic

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

• allow to drastically increase the information storage capacity and complexity of smart materials. In this context, unsymmetrical 1,3,5-tris(arylazo)benzenes – ‘starazos’ – which merge three photoswitches on one benzene ring, were successfully prepared. Two different synthetic strategies, one based on

• 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

• Dreuw and co-workers, who suggested tris(arylazo)benzene 2 (Figure 1) to feature spectrally separated absorption bands for each AB branch. The authors could show that the excited states of the AB branches in tris(arylazo)benzenes were electronically decoupled, despite the spatial overlap. Hence, only

Two new aromatic polyketides from a sponge-derived Fusarium

• Mada Triandala Sibero,
• Tao Zhou,
• Keisuke Fukaya,
• Daisuke Urabe,
• Ocky K. Karna Radjasa,
• Agus Sabdono,
• Agus Trianto and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2019, 15, 2941–2947, doi:10.3762/bjoc.15.289

• with the absorption bands at 234, 266, 313, 499, and 533 nm was closely similar to that for 1-acetyl-2,4,5,7,8-pentahydroxyanthraquinone from a fungus Geosmithia [24], suggesting the presence of a common chromophore in 1. Two highly substituted benzene rings were assembled by analysing the HMBC

• . HMBC correlations from an exchangeable proton at δH 12.57 (4-OH) to C3, C4, and C4a were also supportive of the substitution pattern in this benzene ring. Strong correlations from H6 to C8 and C10a implied the meta-relationship of C8 and C10a to C6, and similarly the ortho-relationship of C5 and C7 to

• (Table 3). Mutual HMBC correlations between two aromatic methines H5 and H7 and their correlations to C8a established their meta-relationship in a benzene ring system. A methoxy group was placed at C6 on the basis of HMBC correlations from H5, H7, and H10 to C6. A sharp singlet resonance at δH 10.94 was

Synthesis and optoelectronic properties of benzoquinone-based donor–acceptor compounds

• Daniel R. Sutherland,
• Nidhi Sharma,
• Georgina M. Rosair,
• Ifor D. W. Samuel,
• Ai-Lan Lee and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2019, 15, 2914–2921, doi:10.3762/bjoc.15.285

• carbazoles with respect to the bridging benzene of ca. 44° in both 3 and 4 (Figure 2). Theoretical properties Density functional theory (DFT) calculations were performed in the gas phase to assess the electronic structures of 2–5 (see Supporting Information File 1 for details). The S1 and T1 excited states

Palladium-catalyzed Sonogashira coupling reactions in γ-valerolactone-based ionic liquids

• László Orha,
• József M. Tukacs,
• László Kollár and
• László T. Mika

Beilstein J. Org. Chem. 2019, 15, 2907–2913, doi:10.3762/bjoc.15.284

• form 2,5-bis(2-phenylethynyl)pyridine (3m) under identical conditions (Table 3, entries 12 and 13). By comparison with the conversion of 4-chloro-1-iodobenzene (1g), no formation of 1,4-bis(phenylethynyl)benzene was detected. It agrees with the activated substituents of 2-substituted pyridine

Preparation of anthracene-based tetraperimidine hexafluorophosphate and selective recognition of chromium(III) ions

• Qing-Xiang Liu,
• Feng Yang,
• Zhi-Xiang Zhao,
• Shao-Cong Yu and
• Yue Ding

Beilstein J. Org. Chem. 2019, 15, 2847–2855, doi:10.3762/bjoc.15.278

• NH4PF6 was performed to generate tetraperimidine hexafluorophosphate 3 with a yield of 85%. Compound 3 was stable to heat, moisture, and air, and it had a good solubility in DCM, DMSO, and CH3CN. In turn, it had a poor solubility in benzene and petroleum ether. In the 1H NMR spectrum of 3, the proton

• + (Supporting Information File 1, Figure S11) produced a distinctive signal at m/z = 587.1086, matching (3⋅Cr3+)/3, again indicating 1:1 complexation. In the IR spectra of 3 and 3⋅Cr3+ (Supporting Information File 1, Figure S12), the C–C absorption band of a benzene moiety in 3 shifted from 1170 to 1185 cm−1

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

• crystal of Pd2(stable E-1)4 formed from a racemic mixture of ligand E-1 suitable for X-ray structure determination was grown by vapor diffusion of a 1:1 mixture of benzene and diethyl ether into a solution of the cage in a 1:1 mixture of acetonitrile and chloroform. The crystal structure shows cage

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

• azoarenes have been ortho-substitution of the benzene ring(s) or replacement of one of the benzenes for a pyrazole (to give arylazopyrazole switches). Here we study the combination of such high-performance features within a single switch architecture. Through computational analysis and experimental

• measurements of representative examples, we demonstrate that ortho-benzene substitution of the arylazopyrazoles drastically increases the Z-isomer stability and allows further tuning of their addressability. This includes the discovery of new azopyrazoles with a Z-isomer thermal half-life of ≈46 years. Such

• . An emerging alternative approach to tune the properties of azoarene photoswitches is to replace one or both of the benzene rings with a heteroaromatic ring [15][16]. While several useful heteroaromatic azo scaffolds have been reported, we previously identified such photoswitches containing a pyrazole