Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• ) [137]. The reaction most likely involves an iminyl radical which undergoes a 5-exo-trig cyclization with the alkene to form the alkyl radical intermediate. Homolytic aromatic substitution (HAS) with the arene will afford the final functionalized product. Interestingly, electron-poor, electron-rich, and

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• groups were tolerated [7]. In 2020, Tan and co-workers disclosed the phosphoric acid-catalyzed atroposelective arene functionalization of nitrosonaphthalene with indoles to form atropisomeric indole-naphthalenes 39 and indole-anilines 40 by a nucleophilic aromatic substitution reaction [61] (Scheme 13

• + 2] formal cycloaddition and central-to-axial chirality conversion. Organocatalytic atroposelective arene functionalization of nitrosonaphthalene with indoles. Proposed reaction mechanism for the atroposelective arene functionalization of nitrosonaphthalenes. Asymmetric construction of axially chiral

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

• Ilya A. P. Jourjine,
• Lukas Zeisel,
• Jürgen Krauß and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2668–2679, doi:10.3762/bjoc.17.181

• also less desirable as reaction intermediates, owing to the difference in their respective reactivity. The results for the route going through N-methyl-2-(aminomethyl)biphenyls 9 are summarized in Scheme 4. We found that substrates bearing electron-donating groups at the aminomethyl carrying arene (9b

• and 9d) afforded significantly lower yields (28 and 34%) than substrates with electron-donating substituents at the other arene (9a and 9c; 59–67%), which were in the same range as the model reaction with unsubstituted amine 2b. Next, reactions with primary 2-(aminomethyl)biphenyls were investigated

• counterpart starting from secondary amine 9b (34%), the trend of electron-donating groups at the aminomethyl carrying arene adversely affecting the yield was also observed for primary amines. The negligible difference in yields for fluorenone 10b starting from amine 15b1 (34%) and 15b2 (38%) respectively

AlBr₃-Promoted stereoselective anti-hydroarylation of the acetylene bond in 3-arylpropynenitriles by electron-rich arenes: synthesis of 3,3-diarylpropenenitriles

• Yelizaveta Gorbunova,
• Dmitry S. Ryabukhin and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2663–2667, doi:10.3762/bjoc.17.180

• hydroarylation of nitriles 1. Reactions of nitriles 1a–c with o-xylene led to the formation of regioisomers derived from the electrophilic substitution at different positions of this arene. Thus, nitrile 1a gave two types of regioisomers 2n and 2o. After reactions of nitriles 1b,c with o-xylene, compounds 2l and

• AlBr3 to both the nitrile and acetylene bonds of the starting compound 1 furnishes the highly electrophilic species A bearing a positive charge on the acetylenic carbon atom C3. The subsequent reaction of species A with the arene molecule via electrophilic aromatic substitution results in the formation

• of species B. The most probably, this stage proceeds stereoselectively due to spatial factors, with the incoming arene Ar′H attacking the acetylene bond in an anti-position to the bulky AlBr3, that determines the final predominant formation of the mainly anti-hydroarylation products of the starting

Synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

• Andrey I. Puzanov,
• Dmitry S. Ryabukhin,
• Anna S. Zalivatskaya,
• Dmitriy N. Zakusilo,
• Darya S. Mikson,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2417–2424, doi:10.3762/bjoc.17.158

• nucleophilic arene molecules, species B should afford substances 5 as products of hydroarylation of the acetylene bond of the starting compounds 3. Indeed, reaction of 5-acetylenyl-1,2,4-oxadiazoles 3a–c with excess of TfOH at room temperature for 1 h resulted in the quantitative preparation of E/Z-isomers of

Facile and innovative catalytic protocol for intramolecular Friedel–Crafts cyclization of Morita–Baylis–Hillman adducts: Synergistic combination of chiral (salen)chromium(III)/BF₃·OEt₂ catalysis

• Karthikeyan Soundararajan,
• Helen Ratna Monica Jeyarajan,
• Raju Subimol Kamarajapurathu and
• Karthik Krishna Kumar Ayyanoth

Beilstein J. Org. Chem. 2021, 17, 2186–2193, doi:10.3762/bjoc.17.140

• the Cr(salen)/BF3·OEt2 catalytic system (5m–r, Table 2). This could be an outcome of steric hindrance exerted by the substitutents at the arene moiety of the MBH adducts. Thereafter, to inspect the utility of the reaction for a gram-scale reaction, we endeavoured a model reaction using the optimized

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• -diarylanthracene 43, so the authors concluded that triarylmethane is an intermediate in the reaction with excess benzaldehyde [43]. In 2009, Olah’s group applied BF3 monohydrate as acid catalyst in arene hydroxyalkylation with aromatic aldehydes, to provide triarylmethane, diarylmethylbenzaldehyde, and anthracene

• propargylic carbonates 113 with terminal alkynes 114. The scope of this reaction consisted of 12 examples that were synthesized in moderate to good yields (40–87%). The authors obtained the best yields by using electron-deficient aryl alkynes or secondary carbonates with electron-rich arene substituents (115a

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• has been selectively feasible without activating a C(sp2)–H bond in the arene moiety. Verma and co-workers [91] have reported the use of VO(acac)2 immobilized over graphitic carbon nitride (VO@gC3N4) under visible light irradiation to perform a photocatalytic C–H activation of arene methides and

• evidence for radical pathways involving vanadium-peroxo species [76], with a few exceptions [95]. Vanadium-based catalysts have been employed in carbon–carbon bond formation reactions, such as arene couplings, thereby proving especially useful in the synthesis of bioactive compounds, including natural

• are crucial. In 2018, Ackermann and co-workers described a novel room temperature C–H arylation by using a continuous visible light photo-flow technique, allied with a manganese photocatalyst CpMn(CO)3 [142]. The new flow protocol enabled the synthesis of several arene- and heterocyclic-based

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• substituent at the arene ring produced predominantly symmetric THP product 26 over the desired trisubstituted heterocycle 23. The mechanism of the reaction was further investigated using enantioenriched homoallylic alcohol (S)-18 with 89% ee, which favored 2-oxonia-Cope rearrangement to give THP 23 only in 14

• activation via DDQ oxidation, followed by nucleophilic attack of an unactivated olefin to obtain all-cis-trisubstituted Prins products with high stereochemical precision [111]. A single-electron transfer (SET) mechanism was proposed for the above transformation (Scheme 69). A SET from an arene or alkene to

Synthesis of bis(aryloxy)fluoromethanes using a heterodihalocarbene strategy

• Carl Recsei and
• Yaniv Barda

Beilstein J. Org. Chem. 2021, 17, 813–818, doi:10.3762/bjoc.17.70

• – the classic Reimer–Tiemann intermediate. This was the case even after the addition of water and continued stirring to allow time for a hypothetical intermediate (bromofluoromethyl)arene to hydrolyze. A general procedure for the production of electron-poor bis(aryloxy)fluoromethanes is to stir

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• electron-withdrawing groups, the scope of the reaction comprises anilines including electron-withdrawing or electron-donating substituents in the arene, except N-acetylated or ortho-halogenated anilines. In 2017, Chen and colleagues [21] reported a method that promoted the formation of an alkoxy radical

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• reported two types of thiacalix[4]arene-protected titanium–oxo clusters [37]. In that work, p-tert-butylthiacalix[4]arene (H4TC4A) was introduced to tetranuclear and hexanuclear clusters Ti4 and Ti6, respectively (Figure 12). The formed hybrid materials had band gaps of 2.19 eV (Ti4) and 2.24 eV (Ti6). The

• titanium–thiacalix[4]arene-based clusters for H2 evolution, and it also provides a useful method for tuning the band gaps of the catalysts. Apart from reducing the distance between the electron donor and acceptor, calixarenes can also promote the charge separation to enhance the electron transfer [38

• ]. Zhou and co-workers employed 4-methoxycalix[7]arene and quartz beads as the host and packing material, respectively (Figure 13). The formed packed bed could then immobilize TiO2. Therein, the 4-methoxycalix[7]arene not only led to a decrease in the band gap of TiO2 but also prohibited the recombination

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• intermediates (triplet aryl cations [28][29] or aryl radicals [30][31]). As for the former case, the intermolecular formation of a biaryl arose from the photoheterolysis of an Ar–N bond (in arene diazonium salts or their derivatives [32][33]), of an Ar–Cl bond [34][35], of an Ar–O bond (in aryl phosphates [36

• ], aryl sulfonates [36], and in aryl trifluoroethyl sulfate [37], Scheme 1a) followed by the reaction of the thus formed aryl cation with an aromatic substrate. In an alternative approach, aryl radicals may be generated under photoredox catalysis conditions (mostly from arene diazonium salts or aryl

• iodides) [30][31] or by the direct photolysis of arylazo sulfones [38][39][40] and employed for the desired arylations. These reactions have the advantage of being applied to non-functionalized arenes but have the drawback to require a large excess of the nucleophilic reagent (the arene Ar–H) in up to 10

Chiral anion recognition using calix[4]arene-based ureido receptors in a 1,3-alternate conformation

• Tereza Horáčková,
• Jan Budka,
• Vaclav Eigner,
• Wen-Sheng Chung,
• Petra Cuřínová and
• Pavel Lhoták

Beilstein J. Org. Chem. 2020, 16, 2999–3007, doi:10.3762/bjoc.16.249

• of calix[4]arene immobilised in the 1,3-alternate conformation led to a system possessing a preorganised ureido cavity hemmed with chiral alkyl units in the near proximity. As shown by the 1H NMR titration experiments, these compounds can be used as receptors for chiral anions in DMSO-d6. The chiral

• highly sophisticated molecules, including anionic receptors [27][28][29][30][31][32][33][34][35][36][37][38][39]. During our ongoing research on anion complexation, we have reported various calix[4]arene receptors based mainly on amide, urea, or thiourea groups [40][41], some of which are available in

• exemplified by our previously published receptors C1 based on a calix[4]arene moiety or by C2 using thiacalix[4]arene as the core scaffold [44][45]. Moreover, the introduction of the tert-butyl groups into the 1,3-alternate conformer should lead to the overall increase rigidity of the molecule, possibly

Construction of pillar[4]arene[1]quinone–1,10-dibromodecane pseudorotaxanes in solution and in the solid state

• Xinru Sheng,
• Errui Li and
• Feihe Huang

Beilstein J. Org. Chem. 2020, 16, 2954–2959, doi:10.3762/bjoc.16.245

• 450001, P. R. China 10.3762/bjoc.16.245 Abstract We report novel pseudorotaxanes based on the complexation between pillar[4]arene[1]quinone and 1,10-dibromodecane. The complexation is found to have a 1:1 host–guest complexation stoichiometry in chloroform but a 2:1 host–guest complexation stoichiometry

• in the solid state. From single crystal X-ray diffraction, the linear guest molecules thread into cyclic pillar[4]arene[1]quinone host molecules in the solid state, stabilized by CH∙∙∙π interactions and hydrogen bonds. The bromine atoms at the periphery of the guest molecule provide convenience for

• the further capping of the pseudorotaxanes to construct rotaxanes. Keywords: host–guest chemistry; pillar[4]arene[1]quinones; pillararenes; pseudorotaxanes; supramolecular chemistry; Introduction Relying on the research of basic science, supramolecular chemistry has become an important mean for

Water-soluble host–guest complexes between fullerenes and a sugar-functionalized tribenzotriquinacene assembling to microspheres

• Si-Yuan Liu,
• Xin-Rui Wang,
• Man-Ping Li,
• Wen-Rong Xu and
• Dietmar Kuck

Beilstein J. Org. Chem. 2020, 16, 2551–2561, doi:10.3762/bjoc.16.207

• offer various possibilities for functionalization. Therefore, TBTQ derivatives have attracted much attention since the first synthesis reported in 1984 [21][22][23][24]. The arene periphery of the TBTQ framework bears a great and variable potential for the efficient expansion of the small and relatively

• , the 1H NMR spectrum of TBTQ-(OAcG)6 exhibits two singlet resonances at δ = 8.62 and δ = 8.58 ppm, each of which indicates three equivalent protons of the six triazole rings. Likewise, two singlets at δ = 7.33 and δ = 7.30 ppm are due to two sets of three equivalent arene protons of the TBTQ core [40

• ten-fold sugar-functionalized pillar[5]arene [43]. Temperature-dependent 1H NMR spectroscopy of TBTQ-(OAcG)6 in DMSO-d6 was carried out in the range of 20–70 °C and revealed a slight decrease of the splitting of the aromatic proton resonances with increasing temperature, but no coalescence. While most

NMR Spectroscopy of supramolecular chemistry on protein surfaces

• Peter Bayer,
• Anja Matena and
• Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

• stabilization of the ligand by additional crystal contacts to neighboring proteins [6][18][20][21][22][26][27][28]. For some supramolecular ligands, like sulfonatocalix[8]arene or phosphonatocalix[6]arene, the tendency to bridge two protein interfaces that do not usually interact in solution goes so far that

• ]arene has been titrated to trimethyl-lysine (KMe3), which yields the largest shifts and most severe line broadening for the methyl protons and Hε resonances, indicating that these atoms are located inside the aromatic bowl of the calixarene [29]. The binding affinities of cucurbituril ligands for

• sulfonato-calix[4]arene binding to Ralstonia solanacearum lectin that was chemically dimethylated on three lysine residues and the N-terminus was studied by 15N-HSQC titrations [50][51]. Both ligands prefer binding to methylated lysines whereby the binding affinity (for the free amino acids) increases with

Palladium nanoparticles supported on chitin-based nanomaterials as heterogeneous catalysts for the Heck coupling reaction

• Tony Jin,
• Malickah Hicks,
• Davis Kurdyla,
• Sabahudin Hrapovic,
• Edmond Lam and
• Audrey Moores

Beilstein J. Org. Chem. 2020, 16, 2477–2483, doi:10.3762/bjoc.16.201

• ChNC or the ChsNC during catalyst fabrication. The lack of metallic Pd peaks present in XRD is indicative of extreme broadening of the reflections of very small Pd NPs within the packets found. Heck coupling is a prominent reaction for arene alkenylation, as the production of stilbene derivatives is

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• alkylation of arenes. The ruthenium-catalyzed meta-selective C–H functionalization through arene σ-activation was already well established yet limited by harsh reaction conditions and elevated reaction temperatures. Both research groups hence hypothesized that the Ru-metallacyclic intermediate, generated via

Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

• Dominik Göbel,
• Marius Friedrich,
• Enno Lork and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139

• of the alkyl bridge between the arene and the azide are underway in our laboratories. Top: literature examples of organic compounds showing RTP in the crystalline state (a) and in solution (b). Bottom: azide-linked derivatives presented in this work. a) Normalized UV–vis absorption spectra of 3 (blue

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

• -workers to be an effective, stable, and recyclable HPCat for a large scope of arene and heteroarene functionalisation reactions, traditionally performed with transition metal complexes (Scheme 2) [128]. The group were able to bifunctionalise N-phenylpyrrole with a variety of functional groups at room

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• the C(sp3) radical, which is intercepted by an organometallic intermediate, obtained by the oxidative addition of a nickel catalyst to the (hetero)aryl bromide 5.2. The desired (hetero)arene product 5.3 is obtained after the reductive elimination of the nickel complex. In this method, the reduced

• /desulfonylation of the arylsulfonyl chlorides 14.1 (Scheme 14) [85][86]. The ensuing aryl radical is trapped by an aryl isonitrile 14.2, affording the bisarylation product 14.3. The direct organophotocatalytic activation of the C–H bond of an arene represents an atom-economical and attractive strategy for the

• cations and radical anions) Recently, the exploitation of alkenyl and aryl radical ions has emerged as a platform for the functionalization of small molecules. They appear as attractive intermediates for a direct alkene difunctionalization or arene C–H functionalization. In particular, radical cations are

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

• )-catalyzed direct C–H borylation [22][23][24][25] gives 2,5,8,11-tetraborylated perylene [26]. The regioselectivity of the perylene borylation is determined by the steric factors rather than by the electron distribution in the arene and this regioselectivity complements that of electrophilic substitutions

Room-temperature Pd/Ag direct arylation enabled by a radical pathway

• Amy L. Mayhugh and
• Christine K. Luscombe

Beilstein J. Org. Chem. 2020, 16, 384–390, doi:10.3762/bjoc.16.36

• published results were replicated, then radical traps were introduced. In these cases, BHT completely eliminated the formation of product 12 and partially inhibited the conversion to product 13. In both cases the arene–BHT adduct was observed by GC–MS as shown in the inset of Scheme 4. While more extensive