Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• enones like D to minimize this route. Interestingly such rigid systems may either be considered as α,β- or β,γ-enone with δ-keto conjugation. However, in one of our previous works [16], we have established that the system should be considered as α,β-enone with δ-keto homoconjugation. Simple β,γ-enone

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• electron-accepting group coupled with various donors connected via a π-conjugation bridge [31][32][33]. Such dyes offer good NLO characteristics when compared to Disperse Red 1 as well as remarkable thermal stabilities with dissociation temperatures up to 300 °C [31][32]. Schiff bases containing an

• corresponding Schiff base derivatives 8–12. However, the Schiff bases 8–12 had higher maximum absorption and emission wavelength values than the dyes 3–7 because of the extended conjugation system present in the Schiff bases. The observation of an intense red shift might be related to a significant contribution

• organic NLO chromophore is related to the presence of donor (D) and acceptor (A) groups linked through a π-conjugation path and is characterized by a large first-order hyperpolarizability value (β). However, a small energy gap between the HOMO and the LUMO (Egap) is an important indicator for high NLO

The B & B approach: Ball-milling conjugation of dextran with phenylboronic acid (PBA)-functionalized BODIPY

• Patrizia Andreozzi,
• Lorenza Tamberi,
• Elisamaria Tasca,
• Gina Elena Giacomazzo,
• Marta Martinez,
• Mirko Severi,
• Marco Marradi,
• Stefano Cicchi,
• Sergio Moya,
• Giacomo Biagiotti and
• Barbara Richichi

Beilstein J. Org. Chem. 2020, 16, 2272–2281, doi:10.3762/bjoc.16.188

• , Poland 10.3762/bjoc.16.188 Abstract Mechanochemistry is an emerging and reliable alternative to conventional solution (batch) synthesis of complex molecules under green and solvent-free conditions. In this regard, we report here on the conjugation of a dextran polysaccharide with a fluorescent probe, a

• the mechanochemical approach (the B & B, ball milling for boronic acid conjugation) as bioconjugation strategy for the labeling of biocompatible carbohydrates. Fluorescent labeling is of key importance to follow up the fate of molecules and (nano)materials inside cells and in the human body. In this

• properties of BODIPY and the biocompatibility of dextran. The BODIPY dextran nanoparticles were characterized regarding their size, morphology, polarity, and toxicity in vitro. We demonstrate the feasibility of mechanochemistry for boronic ester formation [23] to a glycan polymer as a route of conjugation

Tools for generating and analyzing glycan microarray data

• Akul Y. Mehta,
• Jamie Heimburg-Molinaro and
• Richard D. Cummings

Beilstein J. Org. Chem. 2020, 16, 2260–2271, doi:10.3762/bjoc.16.187

• response [13][22][23]. An overview of a typical glycan microarray experiment is provided in Figure 1. The protocol involves the chemical covalent conjugation or noncovalent attachment of glycans (usually 20 up to ≈700 glycans) in multiple replicates and often at varying concentrations to a slide surface

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• mono-substituted sumanene derivatives 49b–d in a stereoselective manner as can be inspected from Scheme 10 [41][42]. In another event, Amaya, Ito, Katoh and Hirao reported a vital building block 53 to extend the π-conjugation bidirectionally through regioselective functionalization (Scheme 11) [43]. To

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

• effect of the electron poor porphyrin should be weak. There are eight bonds between the porphyrin β-position and the pyridine ring including one meta-phenyl connection attenuating the through-bond conjugation. A closer look at the kinetic data in Table 1 (sample I, II, and VII) might give an explanation

Synthesis of 3(2)-phosphonylated thiazolo[3,2-a]oxopyrimidines

• Ksenia I. Kaskevich,
• Anastasia A. Babushkina,
• Vladislav V. Gurzhiy,
• Dmitrij M. Egorov,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2020, 16, 1947–1954, doi:10.3762/bjoc.16.161

• -trifluoromethyl-2-thiouracil (1e) enhances the acidity of the N3H hydrogen by direct conjugation to the carbonyl moiety. As a result, 2-thiouracil 1e acts as an ambident nucleophile. Thus, the attack of the carbon atom attached to the chlorine by the N3 nitrogen atom is accompanied by the elimination of hydrogen

Et₃N/DMSO-supported one-pot synthesis of highly fluorescent β-carboline-linked benzothiophenones via sulfur insertion and estimation of the photophysical properties

• Dharmender Singh,
• Vipin Kumar and
• Virender Singh

Beilstein J. Org. Chem. 2020, 16, 1740–1753, doi:10.3762/bjoc.16.146

• substituents at C1 (R4), compound 4eA with aromatic substituent exhibited better fluorescence due to extended conjugation. The effect of R2 substituent in these derivatives (4bA, 4dA, 4fA and 4gA) was also investigated and it was found that N-alkylation improved the photophysical properties along with higher

Synthesis of Streptococcus pneumoniae serotype 9V oligosaccharide antigens

• Sharavathi G. Parameswarappa,
• Claney L. Pereira and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2020, 16, 1693–1699, doi:10.3762/bjoc.16.140

• acetate loss during isolation, purification, or protein conjugation leads to structurally altered CPS. Vaccines based on synthetic carbohydrate antigens [11][12][13][14][15] such as the first commercially available semisynthetic glycoconjugate vaccine Quimi Hib® against H. influenzae [16] and Shigella

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• sustainable photovoltaics [102], flexible electronics [103], improved organic light emitting diodes (OLEDs) [104], organic field effect transistors (OFETs) [105][106], and more recently, photocatalysts [3][5][10][15]. These materials have semiconducting properties due to extended conjugation producing a

• conjugation and polarisation of the surrounding medium, which is enhanced by low εr(ω) values [115][116][117][118]. The charge is transported in organic materials by “hopping” between the quantum states. The amorphous nature of most polymers produces a low symmetry and anisotropy for the charge transport

• the polymer chain, whereas the FSO-F and FSO-FS polymers had ridged planar chains that facilitated the charge transfer [129]. The FSO-FS dibenzothiophene unit had an extended conjugation onto the sulphur atom in the excited state, which improved the charge delocalisation [129]. This demonstrated that

One-step route to tricyclic fused 1,2,3,4-tetrahydroisoquinoline systems via the Castagnoli–Cushman protocol

• Aleksandar Pashev,
• Nikola Burdzhiev and
• Elena Stanoeva

Beilstein J. Org. Chem. 2020, 16, 1456–1464, doi:10.3762/bjoc.16.121

• and the exocyclic C–C double bond. The geometry of the nitrogen atom is also planar most likely because of conjugation with the exocyclic C–C double bond and the C=O groups. The nitrogen planarity is probably also caused by a hydrogen bond between the NH group and the neighboring carbonyl oxygen atom

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• the case of arylalkyl and diaryl oximes – conjugation of the radical center with π-systems of aryl rings is not observed [47][49][50][67]. It is known that the angular structure is characteristic for the CNO fragment of oxime radicals, and in the case of different substituents at the carbon atom, two

• should also be noted that there is no noticeable decrease in the O–H BDE in diaryl oximes compared to dialkyl oximes (some examples are shown in Figure 4 [71]), which is consistent with the idea that an unpaired electron is delocalized by the conjugation with a lone pair of the nitrogen atom, but not by

• the conjugation with the π-system of the molecule. Figure 4 also shows examples of the calculated values of the O–H BDE of non-oxime compounds with a NOH fragment [71]. The O–H bond in oximes is stronger than in hydroxylamines with a similar structure, except for hydroxylamines with strong electron

Synthesis and properties of quinazoline-based versatile exciplex-forming compounds

• Rasa Keruckiene,
• Simona Vekteryte,
• Ervinas Urbonas,
• Matas Guzauskas,
• Eigirdas Skuodis,
• Dmytro Volyniuk and
• Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 1142–1153, doi:10.3762/bjoc.16.101

• angle values were estimated between the bonded aromatic unit and the respective substituents. All compounds showed large twisting angles that indicated HOMO and LUMO separation and a controlled conjugation distance. In the optimized ground-state geometries, the acceptor and the phenyl units are plane

• they characterize the electron-withdrawing abilities of the quinazoline moiety present in all compounds. The energy bandgap values estimated from CV measurements indicated a more extended π-electron conjugation system for compound 1 compared to compounds 2 and 3. These results correlated well with the

A simple and easy to perform synthetic route to functionalized thienyl bicyclo[3.2.1]octadienes

• Dragana Vuk,
• Irena Škorić,
• Valentina Milašinović,
• Krešimir Molčanov and
• Željko Marinić

Beilstein J. Org. Chem. 2020, 16, 1092–1099, doi:10.3762/bjoc.16.96

• [3.2.1]octadiene compound with an extended conjugation. Keywords: bicyclo[3.2.1]octadiene; photocyclization; thiophene; Vilsmeier–Haack reaction; Wittig reaction; Introduction The bicyclo[3.2.1]octane skeleton has become the subject of intensive research in recent years [1][2][3]. Its presence in

• the bicyclo[3.2.1]octadiene aldehyde 1 and acetone was conducted (Scheme 4). After purification of the reaction mixture the product 12 was obtained. The aim of this experiment was to obtain a system with an extended conjugation of the heteroaromatic moiety under mild conditions, while leaving the

• bicyclic skeleton preserved. The UV spectrum of the aldol product 12, in comparison to the starting aldehyde 1, showed the expected red shift, under the prolonged conjugation in product 12 (Figure 10). Contrary to the results obtained on the styryl analogs 3–7, the preliminary irradiation experiments of

Synthesis of novel multifunctional carbazole-based molecules and their thermal, electrochemical and optical properties

• Nuray Altinolcek,
• Ahmet Battal,
• Mustafa Tavasli,
• William J. Peveler,
• Holly A. Yu and
• Peter J. Skabara

Beilstein J. Org. Chem. 2020, 16, 1066–1074, doi:10.3762/bjoc.16.93

• . The ICT band of 7b at 373 nm was more intense than the ICT band of 7a at 378 nm. This observation confirms that conjugation enhances ICT band intensity [42]. In 7b, the formyl group is at the para position to the carbazole ring, thus giving rise to conjugation. In 7a, however, the formyl group is at

• transport properties with positive solvatochromism. Whilst 7a showed very low emission intensity, 7b showed very high emission intensity. It is noted that the conjugation in compound 7b encompasses the N atom of the carbazole ring and the formyl functionality (viz. the donor/acceptor units of the ICT

• component), whereas the link by conjugation between the same functionalities in 7a is missing. The resulting stronger ICT component in 7b explains the big difference in photophysical properties. Experimental All reagents were standard reagent grade and purchased from Sigma-Aldrich, Merck and Alfa Aesar

Aryl-substituted acridanes as hosts for TADF-based OLEDs

• Naveen Masimukku,
• Dalius Gudeika,
• Oleksandr Bezvikonnyi,
• Ihor Syvorotka,
• Rasa Keruckiene,
• Dmytro Volyniuk and
• Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 989–1000, doi:10.3762/bjoc.16.88

• explained by the dihedral angle between the acridanyl and naphthyl moieties, that is the largest one among all the studied compounds, leading to a reduction of π-conjugation. This observation explains the distinct ICT character of the luminescence of compound 4. The dihedral angles in the molecules of 3 and

Synthesis and properties of tetrathiafulvalenes bearing 6-aryl-1,4-dithiafulvenes

• Aya Yoshimura,
• Hitoshi Kimura,
• Kohei Kagawa,
• Mayuka Yoshioka,
• Toshiki Itou,
• Dhananjayan Vasu,
• Takashi Shirahata,
• Hideki Yorimitsu and
• Yohji Misaki

Beilstein J. Org. Chem. 2020, 16, 974–981, doi:10.3762/bjoc.16.86

• systems; electrochemical properties; extended π-conjugation; digital simulation analysis; tetrathiafulvalene; Introduction Tetrathiafulvalenes (TTFs) with extended π-conjugation have attracted attention as possible components of functional materials, such as molecular conductors, field-effect transistors

Fabclavine diversity in Xenorhabdus bacteria

• Sebastian L. Wenski,
• Harun Cimen,
• Natalie Berghaus,
• Sebastian W. Fuchs,
• Selcuk Hazir and
• Helge B. Bode

Beilstein J. Org. Chem. 2020, 16, 956–965, doi:10.3762/bjoc.16.84

• via conjugation, with Escherichia coli as a donor strain, followed by homologous recombination as described previously [14][22]. This led to a formal ‘knock out’ of the BGC and no production of the respective natural product without induction, whereas induced mutants showed mostly an overproduction of

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

• Phil M. Pithan,
• Sören Steup and
• Heiko Ihmels

Beilstein J. Org. Chem. 2020, 16, 904–916, doi:10.3762/bjoc.16.82

• have shown that depending on the nature of the metal ion, the adopted position relative to the nitrogen and oxygen atoms may vary [82]. In 3a and 3b, the electron density of the phenolate oxygen atom was significantly reduced due to the direct conjugation with the strong electron-accepting

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• , entries 3–7). In contrast, there is no benefit for the ethylphospholene oxides (1h or 4h) (Table 5, entry 8). The olefinicity concept and the olefinicity value (OL%) was developed to measure and describe quantitatively the degree of conjugation of an alkene group with the neighboring functional groups

One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation

• Ji Ma,
• Yubin Fu,
• Junzhi Liu and
• Xinliang Feng

Beilstein J. Org. Chem. 2020, 16, 791–797, doi:10.3762/bjoc.16.72

• extended conjugation of 1 after the annulation. Compound 1 shows a broad absorption band in the range of 449–690 nm with the absorption maximum at 537 nm, which also displays a large red-shift (70 nm) compared with the reported peropyrene derivative [32]. The optical energy gap of 1 is determined to be

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

• were not connected through efficient electronic conjugation/delocalization. Two Q bands were observed in all cases, which is characteristic of zinc porphyrins due to the increased symmetry in the compound as compared to the free base derivatives, which ordinarily feature four Q bands [46]. While the Q

• -known in the literature [4] and results in two distinct Soret bands seen at 418 (23923) and 455 (21978) nm (cm−1) as each porphyrin is electronically isolated due to the lack of orbital overlap between the two units. In stark contrast, the linearly linked butadiyne dimer 20 maintains conjugation between

• emission at 617 nm (16207 cm−1) with two equally intense bands (a characteristic of symmetric porphyrins). The nearly similar λmax of both these dimers reinforces the lack of extended π-conjugation or communication that is present in these molecules. Comparatively, the zinc dimer 9 has an increased

Microwave-assisted efficient and facile synthesis of tetramic acid derivatives via a one-pot post-Ugi cascade reaction

• Yong Li,
• Zheng Huang,
• Jia Xu,
• Yong Ding,
• Dian-Yong Tang,
• Jie Lei,
• Hong-yu Li,
• Zhong-Zhu Chen and
• Zhi-Gang Xu

Beilstein J. Org. Chem. 2020, 16, 663–669, doi:10.3762/bjoc.16.63

• compound 6, which would be quickly converted into 7, a more stable enol form due to its conjugation to the phenyl ring. Conclusion In summary, we have developed a new method for the construction of tetramic acid derivatives by using a one-pot Ugi/Dieckmann cyclization protocol. In comparison with the

Direct borylation of terrylene and quaterrylene

• Haruka Kano,
• Keiji Uehara,
• Kyohei Matsuo,
• Hironobu Hayashi,
• Hiroko Yamada and
• Naoki Aratani

Beilstein J. Org. Chem. 2020, 16, 621–627, doi:10.3762/bjoc.16.58

• tetra-borylated quaterrylene despite a low yield. The post modification of rylenes enables us to prepare their borylated products as versatile units after creating the rylene skeletons. Keywords: borylation; π-conjugation; oligorylene; single crystal X-ray structure; solubility; Introduction Compared