[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• thermal addition of diazo compounds (the well-known carbene precursors), followed by N2 elimination. However, it occurs much more difficultly for diazo compounds than with singlet carbenes. This is due to the formation of a mixture of [5,6]-closed and [6,6]-open isomeric cyclic adducts. This phenomenon

• C60 or b) possible formation of both isomers as a result of 1,3-dipolar cycloaddition of the diazo compound to the fullerene, followed by elimination of molecular nitrogen from the pyrazoline intermediate. Second, the rearrangement of [5,6]-open isomers into thermodynamically more stable [6,6]-closed

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

Breakdown of 3-(allylsulfonio)propanoates in bacteria from the Roseobacter group yields garlic oil constituents

• Anuj Kumar Chhalodia and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2021, 17, 569–580, doi:10.3762/bjoc.17.51

• from 9, followed by a series of proposed spontaneous reactions [5][8]. Through these transformations, acid 10 can undergo a dimerization with elimination of water to allicin (5). The hydrolysis of 5 results in allylsulfinic acid (12) and allyl thiol (13), the latter of which can react with another

• molecule of 5 to yield 10 and 2. Alternatively, 5 can decompose to 10 and thioacroleine (14) by a Cope elimination, which explains the formation of the heterocycles 6 and 7 by dimerization through a [4 + 2] cycloaddition [5]. Compounds 6 and 7 were also reported to be formed from 5 during gas

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

• fragmentation of the ion at m/z = 391.4 Da gave rise to an ion series: 362.4 Da (probably after elimination of HCO), 311.4 Da, 286.3 Da (100%), and 235.4 Da. We did not observe in the tandem spectra the signal after the elimination of copper alone. Similarly, the ESIMS spectrum of an equimolar mixture of

Synthesis of (Z)-3-[amino(phenyl)methylidene]-1,3-dihydro-2H-indol-2-ones using an Eschenmoser coupling reaction

• Lukáš Marek,
• Lukáš Kolman,
• Jiří Váňa,
• Jan Svoboda and
• Jiří Hanusek

Beilstein J. Org. Chem. 2021, 17, 527–539, doi:10.3762/bjoc.17.47

• carbanion, such a base also converts the reactive α-thioiminium group to a much less reactive thioimidate at the same time. The C3 carbanion then preferentially attacks (route c) another molecule of the starting material 1a–e and the resulting adducts undergo a subsequent elimination to give the isoindigo

Deoxygenative C2-heteroarylation of quinoline N-oxides: facile access to α-triazolylquinolines

• Geetanjali S. Sontakke,
• Rahul K. Shukla and
• Chandra M. R. Volla

Beilstein J. Org. Chem. 2021, 17, 485–493, doi:10.3762/bjoc.17.42

• A. This on elimination of a free triazolyl anion generates intermediate B. In next step, the triazolyl anion attacks the electrophilic C2-position of the quinoline N-oxide, providing the intermediate C, which, upon rearomatization, affords the desired 2-triazolylquinoline product 3, along with the

Synthetic strategies of phosphonodepsipeptides

• Jiaxi Xu

Beilstein J. Org. Chem. 2021, 17, 461–484, doi:10.3762/bjoc.17.41

• yields. Good diastereoselectivities were observed with diastereomeric ratios of 84:12 to 88:12 (Scheme 30) [51]. However, when using substrates with arylmethyl groups, the phosphorodichloridites favored an elimination reaction generating the corresponding ethyl cinnamate derivatives during their

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

• step with PPh3 and CHCl3 [11], CCl4 [12], or with the phosphonate reagent LiCCl2-P(O)(OEt)2 [13][14] (Figure 2a). Alternatively, the aldehydes are converted to trichloromethyl carbinols 3 using various methodologies [15][16][17], followed by acetylation and elimination to provide the desired

• -dichloro-1-alkenone 6a in 23% yield, without cleavage of the methyl ether [26] (Scheme 1). A similar AlCl3-promoted conversion of vinylic trifluoromethyl groups to 1,1-dichloroalkenes has previously been reported [27][28]. Additionally, 1,1-dichloroalkenes have also been prepared by the elimination of HCl

• methoxy substituent, and a subsequent elimination of HCl. No such transformation was observed with the other trifluoroalkanone substrates, including the 2- and 4-methoxy substrates 5a and 5f, presumably as only the meta-methoxy group is able to sufficiently activate the two positions adjacent to the

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

• derivatives readily underwent intramolecular Friedel–Crafts-type C–C bond formation followed by dehydration or alcohol elimination, leading to the construction of benzene rings in the biaryl systems (Scheme 2) [20][21]. The reaction proceeded via oxocarbenium ion intermediates stabilized by HFIP. This method

• preparation of cyclization precursors. As described above, the tandem cycloaromatization of the obtained precursors proceeded via Friedel–Crafts-type bond formation followed by elimination, which enabled a rapid and efficient synthesis of helicenes, such as higher-order helicenes, double helical helicenes

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

• solvolysis reaction of 13f, a mixture of the major product 15f, resulting from solvent substitution, and the minor elimination product 16f was observed. Further, 14C labeling experiments on 13f confirmed that the formation of the ion pair 14fOTs was a reversible process [42]. Later, Liu et al. explored the

• -catalyzed condensation mechanism [74][75]. The authors envisioned that substituting a methyl group in isopentenyl pyrophosphate (IPP) by a CF3 group (Scheme 22, 79→78) should greatly reduce the reaction rate in the case of an ionization–condensation–elimination mechanism, while a small acceleration should

• be observed in the case of a displacement–elimination mechanism. Promising results were first obtained during investigations conducted on CF3-substituted derivatives in SN1- and SN2-mechanism-based reactions (Scheme 23). A profound retardation effect for the solvolysis of 81 in acetone–H2O (SN1) with

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

• strongly electron-deficient substituents that finally prevent an acid-catalyzed elimination of hydrazide 2f (vide infra for the mechanism discussion). Finally, the diverse hydroxypyrrolines 1b–e were tested in the studied reaction and the corresponding 1,4-dihydropyridazines 4ba–ea were obtained in 20–51

• intermediate C by the second molecule of hydrazide 2 affords dihydrazone D (similar to previously observed in the recyclization with 2,4-dinitrophenylhydrazine [11]), which further cyclizes to tetrahydropyridazine 3. An acid-catalyzed elimination of hydrazide 2 from tetrahydropyridazine 3 completes the

Diels–Alder reaction of β-fluoro-β-nitrostyrenes with cyclic dienes

• Savva A. Ponomarev,
• Roman V. Larkovich,
• Alexander S. Aldoshin,
• Andrey A. Tabolin,
• Sema L. Ioffe,
• Jonathan Groß,
• Till Opatz and
• Valentine G. Nenajdenko

Beilstein J. Org. Chem. 2021, 17, 283–292, doi:10.3762/bjoc.17.27

• one of the most widely used fluorine-containing building blocks [48][49]. Recently, we have developed an efficient stereoselective synthesis of β-fluoro-β-nitrostyrenes 1 based on the radical nitration of 2-bromo-2-fluorostyrenes [50]. This process takes place with simultaneous elimination of bromine

• expected [80][81][82]. The treatment of norbornene 2l with t-BuOK resulted in the selective elimination of nitrous acid to form the desired monofluorinated norbornadiene 6 in 77% yield. No competitive elimination of HF was observed. The Diels–Alder reaction–base-induced HNO2 elimination sequence opens 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

• halodifluoromethanes and alkenes (Scheme 2). The elimination of hydrogen halide from the halodifluoromethane under basic conditions (metal alkoxide or alkyllithium) generated difluorocarbene [14][15]. The low yields of the product have been attributed to the facile addition of the strong bases to difluorocarbene. The

• methylenecyclopropanes are of interest as Michael acceptors and as substrates for thermal rearrangements. As they are not readily available by difluorocarbene addition to allene derivatives, Taguchi et al. developed an alternative route to these compounds by selenoxide elimination (Scheme 30) [75]. Later, this approach

• bond cleavage occurred regioselectively via difluoroenolate intermediates that could participate in subsequent elimination and substitution of fluoride, leading to good yields of the fluorine-free products 107 and 109 (Scheme 49) [97][98]. Xu and Chen studied the acid-catalyzed hydrolysis of gem

Benzothiazolium salts as reagents for the deoxygenative perfluoroalkylthiolation of alcohols

• Armin Ariamajd,
• Nils J. Gerwien,
• Benjamin Schwabe,
• Stefan Dix and
• Matthew N. Hopkinson

Beilstein J. Org. Chem. 2021, 17, 83–88, doi:10.3762/bjoc.17.8

• heavily fluorinated thiolate anions and the potential for deleterious side-reactions resulting from β-fluoride elimination [28][29][30][31][32][33][34]. Only a handful of perfluoroalkylthiolate salts are known and, to the best of our knowledge, only one general direct nucleophilic perfluoroalkylthiolation

• affords the key electrophilic 2-alkoxybenzothiazolium species A and the perfluoroalkylthiolate anion. Nucleophilic substitution then affords product 3 and thiocarbamate byproduct B. As a side-reaction, β-fluoride elimination from the perfluoroalkylthiolate anion can occur, leading to a thiocarbonyl

• fluoride species, which can subsequently react with the alcohol, delivering thionoester 4. β-Fluoride elimination is a known decomposition pathway of −SCF3 and has even been exploited in synthetic trifluoromethylthiolation and fluorination processes [32][33][34]. The formation of the side-product 4a could

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• elimination (Scheme 1) [35]. The oxazole vinylstannane 24 was prepared from commercially available butyne 21. The tri-n-butyltin hydride addition to 21, followed by Swern oxidation and direct oxazole formation with tosylmethyl isocyanide (TosMIC) gave the fragment 24, which was used immediately for the next

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

• and then subjected to gold catalysis. The synthesis started with the reduction of the N-Ts δ-valerolactam 8 with DIBAL-H into the corresponding lactamol 9 (Scheme 1), which was transformed into the enesulfonamide 10 in 70% yield by mesylation, followed by base-induced elimination of methanesulfonic

• ) [46]. The treatment of 11 with a catalytic amount of trifluoroacetic acid in toluene at 140 °C for 7 min led to the elimination of methanol and provided the 3-iodoenesulfonamide 12 in 77% yield [47]. To avoid the use of these harsh reaction conditions, we employed other methods, but both the

Semiautomated glycoproteomics data analysis workflow for maximized glycopeptide identification and reliable quantification

• Steffen Lippold,
• Arnoud H. de Ru,
• Jan Nouta,
• Peter A. van Veelen,
• Magnus Palmblad,
• Manfred Wuhrer and
• Noortje de Haan

Beilstein J. Org. Chem. 2020, 16, 3038–3051, doi:10.3762/bjoc.16.253

• ). The y- and Y-fragment ions of (glyco)peptides with Cys oxidation showed a characteristic neutral loss of 107.0041 Da (C2H5O2NS), as reported for singly oxidized carbamidomethylated Cys through an elimination reaction in the gas phase (Figures S13 and S16–S18, Supporting Information File 2) [27

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

• tetracyclic compound 56. Dihydroxylation of freshly prepared 56 with OsO4 and then selective tosylation afforded 57 in 39% yield over two steps. Exposure of 57 to DBU upon heating gave the elimination product 58, which was subjected to an oxidative rearrangement with PDC to give enone 59 in 68% yield. Copper

• than C-3’, which results in the regioselective formation of intermediate C. Cyclization of intermediate C gives D and subsequent proton transfer produces isomer E. It undergoes elimination to afford the annulation product 103 and the phosphine catalyst A is regenerated. In the same work, Lu and co

• carbene complex intermediate and a mechanism was proposed (Scheme 10B). An nucleophilic attack of the amine nitrogen onto the alkyne 139 under the effect of activated Pt(II) A produces zwitterionic intermediate B. Elimination of the methoxy group from zwitterion B generates the α,β-unsaturated carbene

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

• practical application, due to the use of labile and expensive reagents. Moreover, the elimination of metal trace residues and wastes is of some concern particularly for products destined to pharmaceutical applications as it is imperative operating under ‘green’ conditions. As for the last issue, there is

Controlled decomposition of SF₆ by electrochemical reduction

• Sébastien Bouvet,
• Bruce Pégot,
• Stéphane Sengmany,
• Erwan Le Gall,
• Eric Léonel,
• Anne-Marie Goncalves and
• Emmanuel Magnier

Beilstein J. Org. Chem. 2020, 16, 2948–2953, doi:10.3762/bjoc.16.244

• ]: They can associate themselves with the F− anions and generate bifluoride HF2 anions or even polyfluorides F(HF). The presence of fluoride anions can produce a Hoffman elimination on the alkyl chain of TBA giving rise to tributylamine, butene, and HF. We can suppose that the anion S2− could also be

Three-component reactions of aromatic amines, 1,3-dicarbonyl compounds, and α-bromoacetaldehyde acetal to access N-(hetero)aryl-4,5-unsubstituted pyrroles

• Wenbo Huang,
• Kaimei Wang,
• Ping Liu,
• Minghao Li,
• Shaoyong Ke and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2920–2928, doi:10.3762/bjoc.16.241

• enamine intermediate I to generate another intermediate III. Subsequently, III underwent an intramolecular electrophilic substitution to form the intermediate IV. Finally, IV underwent an elimination of HBr and a spontaneous aromatization to afford the pyrrole product 4a [48][49]. Apart from the pyrrole

Synthesis of imidazo[1,5-a]pyridines via cyclocondensation of 2-(aminomethyl)pyridines with electrophilically activated nitroalkanes

• Dmitrii A. Aksenov,
• Nikolai A. Arutiunov,
• Vladimir V. Maliuga,
• Alexander V. Aksenov and
• Michael Rubin

Beilstein J. Org. Chem. 2020, 16, 2903–2910, doi:10.3762/bjoc.16.239

• , providing a 2,3-dihydro-1H-imidazo[1,5-a]pyridin-4-ium ion 14. After deprotonation, the latter would form the 2,3-dihydroimidazo[1,5-a]pyridine 15, which after the elimination of O-phosphorylated hydroxylamine, would afford the imidazo[1,5-a]pyridines 16 (Scheme 2). To test this idea, nitroethane (1а, 5

A novel and robust heterogeneous Cu catalyst using modified lignosulfonate as support for the synthesis of nitrogen-containing heterocycles

• Bingbing Lai,
• Meng Ye,
• Ping Liu,
• Minghao Li,
• Rongxian Bai and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2888–2902, doi:10.3762/bjoc.16.238

• of absorbed water [20][21]. Two sharp weight losses were identified on the TG curves as temperature rose. The first loss within 224–327 °C may be caused by decomposition and elimination of the –SO3Na groups and the introduced small organic species in the materials [22], while the second loss at

Fluorine effect in nucleophilic fluorination at C4 of 1,6-anhydro-2,3-dideoxy-2,3-difluoro-β-D-hexopyranose

• Danny Lainé,
• Vincent Denavit,
• Olivier Lessard,
• Laurie Carrier,
• Charles-Émile Fecteau,
• Paul A. Johnson and
• Denis Giguère

Beilstein J. Org. Chem. 2020, 16, 2880–2887, doi:10.3762/bjoc.16.237

• , entry 1). To our delight, mannose analogue 14 was formed as the major product (44% yield), along with 21% of the talose analogue 12 and the elimination product 15 in 20% yield, as determined after analysis of the 19F NMR spectra of the crude reaction mixture. Figure 2 shows a representative 19F NMR

• was formed in 48% yield and with Et3N·1.5HF, compound 14 was formed in 32% yield. It is known that Et3N·3HF/Et3N is more nucleophilic than Et3N·3HF with a limited basicity that reduces the formation of elimination byproducts [32][34]. Then, screening other bases (Table 2, entries 4–6) did not furnish

• elimination byproduct. These results suggest that addition of Et3N dictates the selectivity for the C4 fluorination. With the optimized conditions in hand, we investigated the use of other triflate analogues (Figure 3a). Under optimized conditions (Table 2, entry 2), triflate analogues 16–18 [19] gave

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

• inductive ring opening to v2•+, another hydrogen rearrangement to w2•+, and two α-cleavages to x2•+. Another hydrogen rearrangement and elimination of two hydrogen atoms lead to y2•+ which is identical to z1•+ in the fragmentation mechanism for the base peak ion of 1. Fragmentation mechanisms for