Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

Germacrene B – a central intermediate in sesquiterpene biosynthesis

• Houchao Xu and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2023, 19, 186–203, doi:10.3762/bjoc.19.18

• cations J, showing that a cyclisation of 1 induced by reprotonation at C-4 is not preferred. Also no compounds have been isolated with their structures rigorously elucidated that arise through cation I4. For compounds potentially generated through intermediates I1–I3 the accummulated knowledge will be

• and deprotonation. Guaianes As discussed above, the cyclisation of 1 induced by reprotonation at C-4 to the eudesmane skeleton encounters obstacles because of the formation of secondary cations. Preferentially, reprotonation at C-4 leads to the guaiane skeleton since the formed cations are tertiary

• ) The reprotonation of 1 at C-4 potentially leads to four stereoisomers of cation K, B) reprotonation at C-10 can result in four stereoisomers of L. The sesquiterpenes derived from cations K1, K2 and K4. A) Mechanisms of formation for compounds 53–56, B) pyrolysis of 58 to 53. The sesquiterpenes derived

Total synthesis of insect sex pheromones: recent improvements based on iron-mediated cross-coupling chemistry

• Eric Gayon,
• Guillaume Lefèvre,
• Olivier Guerret,
• Adrien Tintar and
• Pablo Chourreu

Beilstein J. Org. Chem. 2023, 19, 158–166, doi:10.3762/bjoc.19.15

• , as demonstrated by recent studies by Neidig and Lefèvre (Table 2, entry 2) [38]. No alteration of the structure of the active species [Me3FeII]− is observed in the presence of an excess of EtOMgCl, suggesting that the alkoxide additives solely bind to the magnesium cations. However, for very low

• -depth mechanistic studies were so far reported regarding the reactivity of the enol phosphate electrophiles (Scheme 3 and Scheme 4, and Table 2, entry 4). Phosphate free anions released at each catalytic cycle could act either as NMP or alkoxides, that is, as ligands to the magnesium cations, or as

1,4-Dithianes: attractive C2-building blocks for the synthesis of complex molecular architectures

• Bram Ryckaert,
• Ellen Demeyere,
• Frederick Degroote,
• Hilde Janssens and
• Johan M. Winne

Beilstein J. Org. Chem. 2023, 19, 115–132, doi:10.3762/bjoc.19.12

• cation in (3 + 2) cycloadditions: 5,6-dihydro-1,4-dithiin-2-methanol as a stabilized allyl cation Allyl cations are versatile electrophiles for the allylation of various nucleophiles, but can also act as C3-π-systems in a range of cycloaddition reactions (Scheme 13) [84][85][86][87][88]. When combined

• with dienes, a swift (4 + 3) cycloaddition can happen, which is isoelectronic to a Diels–Alder reaction, and amounts to a homo-Diels–Alder reaction (Scheme 13a) [89][90]. Cycloaddition reactions of ‘naked’ unsubstituted allyl cations are usually not synthetically useful, as they lead to a mixture of

• products related to different competing reaction pathways. However, when suitable cation-stabilizing substituents are present, especially on the central carbon atom, very useful transformations can result for the rapid assembly of cycloheptanoid scaffolds [91]. Oxyallyl cations (when Z is an oxygen-based

Combining the best of both worlds: radical-based divergent total synthesis

• Kyriaki Gennaiou,
• Antonios Kelesidis,
• Maria Kourgiantaki and
• Alexandros L. Zografos

Beilstein J. Org. Chem. 2023, 19, 1–26, doi:10.3762/bjoc.19.1

• oxidative decomposition to the core of 194 and 195. FGI followed to complete targets 196–200 (Scheme 16). Pyrroloindoline natural products (Knowles 2018) [102]: In 2018, Knowles’ group demonstrated the ability of TEMPO to act as a trap for radical cations arising from the single-electron oxidation of

Synthetic study toward tridachiapyrone B

• Morgan Cormier,
• Florian Hernvann and
• Michaël De Paolis

Beilstein J. Org. Chem. 2022, 18, 1741–1748, doi:10.3762/bjoc.18.183

• , treatment with KH in DMSO at room temperature caused the degradation of 17. Scarcely examined for this purpose, hydroxide of quaternary ammonium salt was next evaluated to promote the anionic oxy-Cope rearrangement with the prospect that non-coordinating organic cations could facilitate the transformation

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• classified according to the catalytically active species or key intermediates: N-oxyl radicals, oxoammonium cations, amine cation radicals, thiyl radicals, quinones, dioxiranes and oxaziridines, hypervalent iodine compounds, etc. However, some examples of organocatalyzed oxidative processes, in which an

• play an important role in redox-neutral asymmetric organocatalysis by forming nucleophilic enamine intermediates or electrophilic iminium cations. The same principles are used in oxidative transformations, where an amine can play the role of chirality source and the activator of substrate for oxidation

• a nucleophilic reacting center. In addition to umpolung reactions with electrophiles, Breslow intermediates can undergo oxidation with the formation of radical cations or electrophilic acylazolium cations. The acylazolium cation in turn can undergo nucleophilic attack resulting in C–O and C–N

Synthesis and electrochemical properties of 3,4,5-tris(chlorophenyl)-1,2-diphosphaferrocenes

• Almaz A. Zagidullin,
• Farida F. Akhmatkhanova,
• Mikhail N. Khrizanforov,
• Robert R. Fayzullin,
• Tatiana P. Gerasimova,
• Ilya A. Bezkishko and
• Vasili A. Miluykov

Beilstein J. Org. Chem. 2022, 18, 1338–1345, doi:10.3762/bjoc.18.139

• para-substitution of the Cl atoms in the aryl fragments did not significantly effect the oxidation potentials of 1,2-diphosphaferrocenes 8, while the reduction potential of 8b was shifted by 0.33 V to a more negative region as compared to 8c. ORTEP representations for cations 5c (a) and 6c (b) at the

Make or break: the thermodynamic equilibrium of polyphosphate kinase-catalysed reactions

• Michael Keppler,
• Sandra Moser,
• Henning J. Jessen,
• Christoph Held and
• Jennifer N. Andexer

Beilstein J. Org. Chem. 2022, 18, 1278–1288, doi:10.3762/bjoc.18.134

• [33][34]. Under physiological conditions as well as in an in vitro system the actual ΔG may be different by coordination of cations and the ionic strength, temperature and pH of the reaction solution [29][35][36]. Compared to other ATP synthesis reactions very little is known about the thermodynamics

Vicinal ketoesters – key intermediates in the total synthesis of natural products

• Marc Paul Beller and
• Ulrich Koert

Beilstein J. Org. Chem. 2022, 18, 1236–1248, doi:10.3762/bjoc.18.129

• alcohol 56, which was dehydroxylated to the diastereomeric cations VIII and IX. Friedel–Crafts reaction gave diastereomeric lactones 57 and 58. The major diastereomer 58 could be converted to the complex polyphenol (−)-hopeanol (59) in seven further steps. (+)-Camptothecin In the formal synthesis of the

Radical cation Diels–Alder reactions of arylidene cycloalkanes

• Kaii Nakayama,
• Hidehiro Kamiya and
• Yohei Okada

Beilstein J. Org. Chem. 2022, 18, 1100–1106, doi:10.3762/bjoc.18.112

• at the β-position had a significant impact on the reaction. In general, tertiary radicals (or cations) are more stable than secondary ones and therefore, the additional methyl group seems to have a strong steric effect (Figure 3). If so, tying up the two methyl groups as a cyclopropane ring may

• . Formal expression of radical cations. Radical cation Diels–Alder reaction of β-methylstyrene. Radical cation Diels–Alder reaction of β-methylanethole (1). Recovered starting material is reported in parentheses. Radical cation Diels–Alder reactions of the arylidene cycloalkanes (4–7). Recovered starting

First example of organocatalysis by cathodic N-heterocyclic carbene generation and accumulation using a divided electrochemical flow cell

• Daniele Rocco,
• Ana A. Folgueiras-Amador,
• Richard C. D. Brown and
• Marta Feroci

Beilstein J. Org. Chem. 2022, 18, 979–990, doi:10.3762/bjoc.18.98

• known salts, at present used in a wide variety of chemical fields. The first definition of ionic liquids was given by Paul Walden in 1914: “they are materials composed of cations and anions, that melt around 100 °C or below as an arbitrary temperature limit” [1]. ILs are salts formed by non or weakly

• coordinated cations and anions, usually bulky organic cations and inorganic or organic anions such as −BF4, −PF6, −N(CF3SO2)2, etc. [2][3]. The physicochemical properties of RTILs (room temperature ionic liquids) are reported in the literature and include very low vapor pressure, and thus the possibility to

Understanding the competing pathways leading to hydropyrene and isoelisabethatriene

• Shani Zev,
• Marion Ringel,
• Ronja Driller,
• Bernhard Loll,
• Thomas Brück and
• Dan T. Major

Beilstein J. Org. Chem. 2022, 18, 972–978, doi:10.3762/bjoc.18.97

• -house code which modifies parameters for cations from existing parameters for neutral molecules. For each intermediate in the reaction mechanism (path HP and IE) we created 100 conformers which were subsequently clustered (a cluster width of 1.0 Å was used). For each unique conformer we performed QM

Electrochemical and spectroscopic properties of twisted dibenzo[g,p]chrysene derivatives

• Tomoya Imai,
• Ryuhei Akasaka,
• Naruhiro Yoshida,
• Toru Amaya and
• Tetsuo Iwasawa

Beilstein J. Org. Chem. 2022, 18, 963–971, doi:10.3762/bjoc.18.96

• , dyes, liquid crystals, and light-emitting materials. A number of substituted DBCs have been reported in this context [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. To develop charge-transport materials, Rathore et al. reported on the stability of radical cations of

Synthesis and HDAC inhibitory activity of pyrimidine-based hydroxamic acids

• Virginija Jakubkiene,
• Gabrielius Ernis Valiulis,
• Markus Schweipert,
• Asta Zubriene,
• Daumantas Matulis,
• Franz-Josef Meyer-Almes and
• Sigitas Tumkevicius

Beilstein J. Org. Chem. 2022, 18, 837–844, doi:10.3762/bjoc.18.84

• ) cap [1][2][5]. One of the most commonly used zinc chelating groups in HDACs inhibitors is a hydroxamic acid moiety (–CONHOH) [6][7][8][9][10][11][12][13][14][15]. The ability of hydroxamic acids to form chelates with various metal cations, including the Zn2+ ion found in the catalytic center of most

Synthesis of piperidine and pyrrolidine derivatives by electroreductive cyclization of imine with terminal dihaloalkanes in a flow microreactor

• Yuki Naito,
• Naoki Shida and
• Mahito Atobe

Beilstein J. Org. Chem. 2022, 18, 350–359, doi:10.3762/bjoc.18.39

• used because this leads to different ion-pair interactions with the radical anion intermediate. To confirm this conjecture, we carried out the model reaction using perchlorate salts consisting of cations of different sizes. As shown in entry 2 of Table 5, when Et4N∙ClO4 was used as the supporting

Mechanistic studies of the solvolysis of alkanesulfonyl and arenesulfonyl halides

• Malcolm J. D’Souza and
• Dennis N. Kevill

Beilstein J. Org. Chem. 2022, 18, 120–132, doi:10.3762/bjoc.18.13

• this system when, under a later subheading, we discuss applications of the extended Grunwald–Winstein equation [36][37][38][39]. Sulfonyl chlorides have relatively high heterolytic bond-dissociation energies [50] indicating that under the usual solvolytic conditions the formation of sulfonyl cations

• SO2Cl− ion or as SO2 + Cl−) (Equation 5). It would be of interest to extend this study to other RSO2Cl substrates, where the R forms a relatively stable carbocation, such as the 1-adamantanesulfonyl chloride and/or the diphenylmethanesulfonyl chloride [(C6H5)2CHSO2Cl], examples with intermediate cations

Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

• Jolita Bruzgulienė,
• Greta Račkauskienė,
• Aurimas Bieliauskas,
• Vaida Milišiūnaitė,
• Miglė Dagilienė,
• Gita Matulevičiūtė,
• Vytas Martynaitis,
• Sonata Krikštolaitytė,
• Frank A. Sløk and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11

• asymmetric unit of the crystal of 6b consists of two (2S)-2-[4-(methoxycarbonyl)-1,2-oxazol-5-yl]piperidin-1-ium cations and two 2,2,2-trifluoroacetate anions (2C10H15N2O3+·2C2F3O2−) (Figure 5; Table 1, Supporting Information File 1 in Tables S1–S3). The substituted piperidinium moieties are in chair

• 1.44 ppm. ORTEP diagram of the asymmetric unit consisting of two cations 6b(A) and 6b(B) and triflate anions. Conversion of cyclic amino acids to 1,2-oxazole derivatives. Plausible mechanisms for the formation of 1,2-oxazoles 4a–h and VII from β-enamino ketoesters 3a–h with hydroxylamine. Synthesis of

DABCO-promoted photocatalytic C–H functionalization of aldehydes

• Bruno Maia da Silva Santos,
• Mariana dos Santos Dupim,
• Cauê Paula de Souza,
• Thiago Messias Cardozo and
• Fernanda Gadini Finelli

Beilstein J. Org. Chem. 2021, 17, 2959–2967, doi:10.3762/bjoc.17.205

• abstractor in photocatalytic strategies could expand the catalyst combinations, as illustrated in Figure 1, to create new and exciting methodologies and improve the understanding on theoretical aspects of the HAT process with nitrogen radical cations. However, despite its promising chemical properties and

• catalysts and photocatalysts [9][10][11][12][21][22][23]. Previous reports of DABCO as hydrogen abstractor in HAT reactions and this work. Free energy profile for the HAT step reactions between isovaleraldehyde with (top) DABCO and (bottom) quinuclidine radical cations. The red lines are for the gas phase

Synthesis of a novel aminobenzene-containing hemicucurbituril and its fluorescence spectral properties with ions

• Qingkai Zeng,
• Qiumeng Long,
• Jihong Lu,
• Li Wang,
• Yuting You,
• Xiaoting Yuan,
• Qianjun Zhang,
• Qingmei Ge,
• Hang Cong and
• Mao Liu

Beilstein J. Org. Chem. 2021, 17, 2840–2847, doi:10.3762/bjoc.17.195

• produced the desired amidobenzene-containing hemicucurbituril. As an original fluorescent chemosensor, it exhibited strong interactions with Fe3+ over other metal cations. The experimental evidence of fluorescence spectra suggested that a 1:1 complex was formed between this macrocycle and Fe3+ with an

• as reactive sites for derivatization, at the same time allowing for formation of coordination or hydrogen bonds with guests, and the aminobenzene unit as a chromophore could improve the optical properties. With this novel macrocycle in hand, the interactions with some metal cations have been

• initially studied. Among the metal cations examined, the fluorescence intensity of macrocycle 4 quenched significantly when adding the corresponding equivalents of Fe3+ and Cu2+. Notably, this macrocyclic host molecule formed 1:1 complexes with Fe3+ in DMF with an association constant up to (2.1 ± 0.3

Targeting active site residues and structural anchoring positions in terpene synthases

• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2021, 17, 2441–2449, doi:10.3762/bjoc.17.161

• large active site cavity SmTS1 exhibits a few notable features within its amino acid sequence. The aspartate-rich motif, that is usually composed of DDXX(X)D and is responsible for binding of two Mg2+ cations (Figure 1) [11][21], is modified to N86DLTV in SmTS1. Similarly, the NSE triad for binding of

• spheres represent Mg2+ cations and orange/red sticks show complexed diphosphate. Products and relative activities of SmTS1 and its variants. Bars left of the dashed line show relative total sesterterpene production (wildtype = 100%), bars right of the dashed line show relative production of individual

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

• expect the formation of similar dications at the protonation of acetylenyloxadiazoles 3 in Brønsted superacids (see Table 1). Table 1 contains data on DFT calculations of cations Aa–d (N-protonated forms) and Ba–d (N,C-diprotonated forms) derived at the protonation of oxadiazoles 3a–d. Charge

• of E/Z-vinyl triflates 4a–c from 5-acetylenyl-1,2,4-oxadiazoles 3a–c in TfOH. Formation of compound 4d from 5-acetylenyl-1,2,4-oxadiazole 3a in H2SO4. Hydroarylation of 5-acetylenyl-1,2,4-oxadiazole 3a–d by arenes in TfOH leading to compounds E/Z-5a–g. Selected electronic characteristics for cations

Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• [86]. Besides the contact to the chloride anion, investigations with tetrabutylammonium chloride (TBACl) and pyridinium chloride salt as model compounds found evidence for productive interactions between the catalyst and the cations. However, these interactions may not solely be attributed to cation–π

Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• protonation of 17 and 18 by TFA resulted in a large red-shifted broad absorption band in the 500–900 nm region due to the formation of azulenium cations in the polymer backbone unlike the 1,3-polyazulene 5, which had no significant effect on its absorption spectrum upon protonation. The HOMO–LUMO gap for the

• tropylium cations can be achieved by incorporating the seven-membered rings of azulene in the polymer backbone. The enhanced stability of these 4,7-polyazulenes 17–20 in acids and their stimuli-responsible behavior make them potential materials for photonic device applications. Poly[2,6-aminoazulene] In

• , respectively. The UV–vis absorption features of polymers 115 and 116 were altered upon protonation due to the formation of azulenium cations in the polymer backbone and they displayed a significant color change on protonation. None of these polymers were fluorescent in the neutral form, however, 115 and 116

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• process, where hydrosilanes 41 were treated with an excess amount of indoles (Scheme 7a and Scheme 7b) [60]. Brookhart’s acid [H(OEt2)2]+[BArF4]− (42) was used to generate ether-stabilized silicon cations of type 46 and norbornene was added as a proton scavenger [64]. Following this procedure, Yonekura