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

• additive to give corresponding thiophene radical 76 and aniline radical cation under irradiation with light. Then, 76 reacted with 73, giving rise to corresponding radical 77. Finally, product 74 was given via hydrogen atom transfer (Scheme 26). In contrast to (hetero)aryl halides with indispensable

• occurs, giving radical 146 and radical cation 147, respectively. Finally, radical 146 undergoes decarboxylation to afford an aryl radical and then combines with radical cation 147, yielding product 144 (Scheme 50). It should be noted that only when NHPI is firstly activated can it turn into an electron

Synthesis, structural characterization, and optical properties of benzo[f]naphtho[2,3-b]phosphoindoles

• Mio Matsumura,
• Takahiro Teramoto,
• Masato Kawakubo,
• Masatoshi Kawahata,
• Yuki Murata,
• Kentaro Yamaguchi,
• Masanobu Uchiyama and
• Shuji Yasuike

Beilstein J. Org. Chem. 2021, 17, 671–677, doi:10.3762/bjoc.17.56

• approximately 50 nm longer than that of our oxide 3 [16]. The fluorescence wavelength, including the maximum emission (λem), and the quantum yield depend on the nature of the P-modification. Phosphine oxide 3, cation 5, and boron complex 6 emitted blue fluorescence in the visible-light region, with λem at 395

• –426 nm (Table 2). P-methylated cation 5 exhibited the longest wavelength and the highest quantum yield. The electrochemical properties of benzonaphthophosphoindoles were investigated by using cyclic voltammetry, and the electrochemical data are summarized in Table 3 and Figure S4, Supporting

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• and the possible product contamination by homogeneous catalysts [199]. The conventional catalysts for this reaction are EG-soluble metal acetates, the activity of which showed a decrease in the order Zn2+ > Mn2+ > Co2+, which was attributed to the diverse interaction between the metal cation promoter

• , based on the activation of the C=O bond by the IL Lewis acid cation and of the hydroxy group in EG by the IL anion (Scheme 6). The IL catalysts could be easily separated by distillation and reused up to six times with no significant efficiency drop. Catalytic glycolysis by heterogenised, metallated

Amino- and polyaminophthalazin-1(2H)-ones: synthesis, coordination properties, and biological activity

• Zbigniew Malinowski,
• Emilia Fornal,
• Agata Sumara,
• Renata Kontek,
• Karol Bukowski,
• Beata Pasternak,
• Dariusz Sroczyński,
• Joachim Kusz,
• Magdalena Małecka and
• Monika Nowak

Beilstein J. Org. Chem. 2021, 17, 558–568, doi:10.3762/bjoc.17.50

• HCl/CO or 2) with the loss of HCl/N2 (≈64 Da). In both cases, the pyridazinone moiety undergoes degradation to different ions 11, 12 with the same m/z = 287.3 and 289.3 Da. In the next stage, the copper cation is detached to form ions 13 and 14 (224.3 Da) indicating that the copper is well fitted into

Unexpected rearrangements and a novel synthesis of 1,1-dichloro-1-alkenones from 1,1,1-trifluoroalkanones with aluminium trichloride

• Beatrice Lansbergen,
• Catherine S. Meister and
• Michael C. McLeod

Beilstein J. Org. Chem. 2021, 17, 404–409, doi:10.3762/bjoc.17.36

• ), a single product was isolated from the reaction that, after careful elucidation (see Supporting Information File 1), was identified as the bicycle 17. This compound could potentially arise via an initial conversion to the dichloroalkyl cation 18, followed by a ring closure and elimination of HCl to

Helicene synthesis by Brønsted acid-catalyzed cycloaromatization in HFIP [(CF₃)₂CHOH]

• Takeshi Fujita,
• Noriaki Shoji,
• Nao Yoshikawa and
• Junji Ichikawa

Beilstein J. Org. Chem. 2021, 17, 396–403, doi:10.3762/bjoc.17.35

• bisacetal precursors, which were readily prepared through C–C bond formation by Suzuki–Miyaura coupling. This cyclization was efficiently realized by a catalytic amount of trifluoromethanesulfonic acid (TfOH) in a cation-stabilizing solvent, 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP), which readily allowed

• types of helicenes using a sequence of (i) Suzuki–Miyaura coupling of acetal-containing components and (ii) catalytic cycloaromatization with the aid of a cation-stabilizing fluoroalcohol, HFIP, as solvent. Particularly, helicene synthesis using tandem cyclization of bisacetals with teraryl structures

Mesoionic tetrazolium-5-aminides: Synthesis, molecular and crystal structures, UV–vis spectra, and DFT calculations

• Vladislav A. Budevich,
• Sergei V. Voitekhovich,
• Alexander V. Zuraev,
• Vadim E. Matulis,
• Vitaly E. Matulis,
• Alexander S. Lyakhov,
• Ludmila S. Ivashkevich and
• Oleg A. Ivashkevich

Beilstein J. Org. Chem. 2021, 17, 385–395, doi:10.3762/bjoc.17.34

• -regioisomers (152–156 and 143.4 ppm for 1-methyl-5H-tetrazole) [31]. The de-tert-butylation selectivity observed for compound 11b can be explained by the higher stability of the t-Bu cation versus the Me cation. Crystal structures The mesoionic compounds 8a, 10, 11a, and salt 9 were characterized by single

• cation, shown in Figure 2, and two bromide anions. The structure of the cation is close to C2 symmetry, with an rms deviation of its non-hydrogen atoms from ideal positions of 0.1320 Å. In the salt 9, the lengths of the tetrazole ring bonds and the exocyclic C–N bond are given in Table 3 together with

• derivatives. Molecules of compounds 8a, 10, 11a, and the bistetrazolium cation 9, with displacement ellipsoids drawn at the 50% probability level. The hydrogen atoms are shown as spheres of arbitrary radii. The atom numbering is done for the asymmetric unit. Experimental (a) and TD-tHCTHhyb/6-311+G(2d,p

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• material sciences [14][15][16][17]. In this context, deciphering the impact that can be exerted by the trifluoromethyl group on a cation and the associated consequences when facing the challenge of developing innovative synthetic methods are the subjects of this review. Review Quantitative parameters

• alkylcarbenium ions, in which a higher electronic contribution from neighboring substituents is required. Detailed ab initio studies have been focused on the stability of the CF3CH2+ cation and provide pieces of thoughts on the origins of the stabilizing interactions in α-(trifluoromethyl)carbenium ions. The

• optimization of the geometry for CF3CH2+ at the STO-3G level led to an energy minimum, in which one of the fluorine atoms is significantly closer to the positive carbon center (Figure 1, top, θ = 101°) [24]. However, exactly the same structural distortion was calculated for the ethyl cation. Furthermore, the

Hydrazides in the reaction with hydroxypyrrolines: less nucleophilicity – more diversity

• Dmitrii A. Shabalin,
• Evgeniya E. Ivanova,
• Igor A. Ushakov,
• Elena Yu. Schmidt and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2021, 17, 319–324, doi:10.3762/bjoc.17.29

• (Scheme 4). A proposed mechanism for the recyclization of hydroxypyrrolines 1 with hydrazides 2 is shown in Scheme 5. The protonation of the starting hydroxypyrroline 1 with TFA leads to the formation of cation A, which reacts with hydrazide 2 to give the pyrrolidine derivative B. The latter undergoes a

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• - or dibromomethyl carbanions. The so-obtained carbanions form lipophilic ion pairs with the catalyst cation and move into the organic phase, where they react with dibromodifluoromethane. Consequently, carbon tetrabromide (or bromoform) and the ion pair CBrF2−N+Bu4 are formed. The ion pair decomposes

• by a dipolar resonance structure containing the 2-fluoroallyl cation and fluoride anion (Scheme 39). A subsequent comparison of the rates of racemization with those of epimerization confirmed experimentally the preference for coupled disrotatory motions in the opening and closing of 2,3-dialkyl-1,1

• opening was attributed to the stabilization of the developing cationic center by the +M effect of the fluorine atoms. The formation of the 2,2-difluorohomoallyl cation or 3,3-difluorocyclobutyl cation did not occur as a result of the strong destabilization by the −I effect of the fluorine atoms [96]. On

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

• MicroCal ITC data analysis software for Origin 7.0. Top: pelargonidin cation (Flavy) and network of chemical reactions; bottom: corresponding UV–vis spectra of the different states of Flavy. Characterization of Flavy: a) 1H NMR spectrum at pH 7.0 (form A) before and after irradiation; b) 13C NMR spectrum

Novel library synthesis of 3,4-disubstituted pyridin-2(1H)-ones via cleavage of pyridine-2-oxy-7-azabenzotriazole ethers under ionic hydrogenation conditions at room temperature

• Romain Pierre,
• Anne Brethon,
• Sylvain A. Jacques,
• Aurélie Blond,
• Sandrine Chambon,
• Sandrine Talano,
• Catherine Raffin,
• Branislav Musicki,
• Claire Bouix-Peter,
• Loic Tomas,
• Gilles Ouvry,
• Rémy Morgentin,
• Laurent F. Hennequin and
• Craig S. Harris

Beilstein J. Org. Chem. 2021, 17, 156–165, doi:10.3762/bjoc.17.16

• a sacrificial metal cation, preventing Pd ligation and permitting the reaction to turnover resulting in albeit poor isolated yields of 9d,e (Table 2). All attempts to carry out the reaction using only CuI failed, confirming that Pd was necessary to catalyze this transformation. It was preferential

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

• repeating unit. The term "crown" is derived from the resemblance of the crown ether when bound to a cation with a crown sitting on a head. The most common crown ethers are those of ethylene oxide. The exterior of the ring is hydrophobic, while the oxygen atoms within the ring can strongly coordinate to a

• cation, forming complexes. Crown ethers also contain a series of derivatives, such as aza-crowns, where the ether oxygen atoms are replaced by amino groups. A well-known tetrazacrown is cyclen. Due to the excellent host–guest properties of crown ethers, they play a very important role in the construction

• of two different crown ether-substituted molecules, styrylbenzothiazole and cinnamic acid [18]. In this system, the Ba2+ cation can preorganize the two crown ether-substituted molecules into a supramolecular complex (Figure 2), which was further stabilized by hydrogen bonding and π–π interactions

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• hydride, known as Schwartz’s reagent [8]. This reduces the amide moiety, giving a complex that can be readily transformed into an imine or iminium cation [9]. It may perhaps be observed without straying too far afield from our primary focus that reduction of amides is actually not a leading use case of

• oxocarbenium ion is substituted, two diastereomeric half-chair conformers are possible: 3H4 and 4H3 (shown for a 4-substituted pyranose cation in Scheme 5). Both may undergo attack by a nucleophile in two ways: on the axial trajectory from the top or the bottom face. Such an event would result in the formation

Synthesis of aryl 2-bromo-2-chloro-1,1-difluoroethyl ethers through the base-mediated reaction between phenols and halothane

• Yukiko Karuo,
• Ayaka Kametani,
• Atsushi Tarui,
• Kazuyuki Sato,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2021, 17, 89–96, doi:10.3762/bjoc.17.9

• ]. Recent studies demonstrated an electrophilic character of a gem-difluorovinyl carbon due to the overlapping of the fluorine lone pairs and the adjacent π orbital in favor of the generation of a difluoromethyl cation species [44]. Considering these reports, the phenoxide attack on the gem-difluorovinyl

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• piperidine derivatives 1 because of the accelerating effect of the nitrogen atom that stabilizes the oxyallyl cation intermediate 4 formed upon the ring closure. This was in analogy to that found for the classical Brønsted or Lewis acid-catalyzed Nazarov reaction involving N-heterocycles [27][28][29][30][31

• species to the alkyne 5, as in I (Figure 2). The first step TS1 has a low activation energy (ΔG‡ = 12.2 kcal⋅mol−1) to form the unstable cyclic intermediate II. This short-lived species rapidly reopens through TS2 (ΔΔG‡ = 8.1 kcal⋅mol−1) to give the pentadienyl cation III, which presents a high stability

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• transformation of 149 to phyllocladanol (21) was accomplished in four steps. In 2016, Winne and co-workers reported that (5,6-dihydro-1,4-dithiin-2-yl)methanol (151) can be served as a allyl-cation equivalent for the [3 + 2] cycloaddition and was applied in the synthesis of (±)-cuparene (13) [69] (Scheme 12B

• take place. The use of noncyclic analogues did not give the cycloaddition product. It is suggested that the restricted rotational freedom of 151 and the related enforced conjugation of the sulfur lone pair may block certain undesired cation reactions. Cycloaddition product 154 was subjected to the

• tetrachloride produces an alkyoxy allylic carbocation (not shown). This carbocation is subjected to a regiospecific electrophilic substitution of allene 168 to generate a vinyl cation 172, which is stabilized by an adjacent carbon–silicon bond. The 1,2-shift of the silyl group in 172 produces an isomeric vinyl

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

• ], 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

• –20-fold amount. Furthermore, the aryl radical/cation addition onto the aromatic reactant may lead to a mixture of regioisomers when using non-symmetrical Ar–H. A possible solution is having recourse to an intramolecular free radical ipso substitution reaction where an XSO2 tether is placed between

On the mass spectrometric fragmentations of the bacterial sesterterpenes sestermobaraenes A–C

• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2020, 16, 2807–2819, doi:10.3762/bjoc.16.231

• radical cation 1•+ is obtained from which the methyl group C23 can directly be lost by an α-cleavage leading to fragment a1+ (Scheme 1A). However, the radical centred at the bridgehead carbon C11 is orthogonal to, or in other words, not in conjugation with the radical cation at C12–13. Therefore, an

• group C23 results in j1+ (Scheme 1E). The fragmentation of the C25–3–4 portion can be explained starting from 1•+ by a hydrogen rearrangement to k1•+ and α-cleavage to l1•+ (Scheme 1F). Another hydrogen rearrangement combined with an α-fragmentation then leads to the allyl cation m1•+ which may undergo

3-Acetoxy-fatty acid isoprenyl esters from androconia of the ithomiine butterfly Ithomia salapia

• Florian Mann,
• Daiane Szczerbowski,
• Lisa de Silva,
• Melanie McClure,
• Marianne Elias and
• Stefan Schulz

Beilstein J. Org. Chem. 2020, 16, 2776–2787, doi:10.3762/bjoc.16.228

• , formed by a 1,10-cyclization of the farnesyl cation 5 obtained from farnesyl pyrophosphate (4) (Scheme 2). Trapping the cation 6 with water leads to 7, which in turn might rearrange into 8 [22]. The fatty acid ester composition also differed between the two subspecies (Figure 2). Based on their elution

• explained by the different stabilization of the respective ions (Figure 3). The abundance of m/z 68 is higher in isoprenyl esters due to the more stable allyl radical cation (Figure 3A). In contrast, prenyl ester fragmentation produces a stabilized allyl cation m/z 69 (Figure 3B), while isoprenyl esters

• form a less stable homoallyl cation. This situation changes when a double bond is present in the acid part. In both isoprenyl (9) and prenyl esters (10) ion m/z 69 becomes the base peak, but the proportion of m/z 68 is higher in the former esters (Figure 4). Other significant differences can be found

A heterobimetallic tetrahedron from a linear platinum(II)-bis(acetylide) metalloligand

• Matthias Hardy,
• Marianne Engeser and
• Arne Lützen

Beilstein J. Org. Chem. 2020, 16, 2701–2708, doi:10.3762/bjoc.16.220

• , each iron(II) cation is coordinated by three pyridylimine chelates. Supporting Information Supporting Information File 476: Collection of the different NMR spectra recorded from heterobimetallic metallosupramolecular tetrahedron 4 and details regarding the energy-minimized structures of 4. Funding

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany Department of Chemistry, University of Jyvaskyla P. O. Box 35, 40014 Jyväskylä, Finland 10.3762/bjoc.16.209 Abstract Crown ethers are common building blocks in supramolecular chemistry and are frequently applied as cation sensors or as subunits in

• alkali metal ions [2]. Crown ethers and their binding properties nowadays find frequent application, e.g., as cation sensors [4][5][6][7], as phase-transfer catalysts [8][9][10], or as drug delivery systems [11][12][13]. Already at the early stages of crown ether research, considerable effort has been

• ferrocene [14][17]. Yet, switchable crown ethers are also widely applied as cation sensors, where the sensor activity can be controlled by external stimuli, e.g., light, the redox potential or chemical reagents [14][17]. Redox-switchable crown ethers have been shown to sense cations by the generation of an

Synthesis of novel fluorinated building blocks via halofluorination and related reactions

• Attila Márió Remete,
• Tamás T. Novák,
• Melinda Nonn,
• Matti Haukka,
• Ferenc Fülöp and
• Loránd Kiss

Beilstein J. Org. Chem. 2020, 16, 2562–2575, doi:10.3762/bjoc.16.208

• process, an alkene reacts with a halogen cation to form a halonium ion, which immediately undergoes ring opening by fluoride to form a vicinal halofluoride (see Scheme 1). The overall result is an anti-addition of the XF moiety (X = Cl, Br, I) across the double bond. Since many nucleophilic fluorine

• the absence of the reagent. It is also worth mentioning that the bromolactone (rac)-17a was surprisingly stable against lactone ring-opening: the compound remained intact after 20 hours of reflux in methanol in the presence of a catalytic amount of H2SO4. Presumably, the halogen cation attacks from

• the larger iodine cation to a greater extent. With this in mind, we also tried the chlorofluorination of compound 19. Again, two chlorofluorinated products were formed, but only (rac)-20c could be isolated in a pure form (Scheme 12). Chlorofluorination is usually inferior in terms of the yield when

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

• ]•+, with the latter oxidising 22 to give radical cation 22•+ and turn over the photocatalytic cycle. The radical cation 22•+ is then proposed to participate in a two-step electron and proton exchange process with [CoII] to give [H–CoIII] and iminium ion 24, likely via a [CoI] intermediate. [H–CoIII] can

• investigations [21] showed that after excitation of the EDA complex, the electrophilic radical 40• that is formed enters the same chain propagation cycle as in Scheme 1, whereas the radical cation 41•+ is proposed to be unstable and decomposes. The third approach, also developed by Melchiorre et al., was based

• = 0.22), so a chain mechanism is likewise unlikely. Interestingly, Melchiorre later found that with α-amino silanes 60, no photocatalyst was required (Scheme 8) [41]. This was proposed to be due to the formation of an intramolecular EDA complex, which upon excitation can form cation 61+ that can

Design and synthesis of a bis-macrocyclic host and guests as building blocks for small molecular knots

• Elizabeth A. Margolis,
• Rebecca J. Keyes,
• Stephen D. Lockey IV and
• Edward E. Fenlon

Beilstein J. Org. Chem. 2020, 16, 2314–2321, doi:10.3762/bjoc.16.192

• exhibit this behavior. Two separate triazole peaks were observed (8.19 and 8.38 ppm), consistent with a new triazole ring being formed. The mass spectrum of the product showed peaks for the expected mass of the TLC product(s) and various cation adducts: (peak mass, assignment, relative intensity): 1563.9