HFIP as a versatile solvent in resorcin[n]arene synthesis

• Hormoz Khosravi,
• Valeria Stevens and
• Raúl Hernández Sánchez

Beilstein J. Org. Chem. 2024, 20, 2469–2475, doi:10.3762/bjoc.20.211

• limitation, we analyzed the mechanism underlying the formation of resorcin[n]arenes. The first step of the cyclization reaction is a hydroxyalkylation involving various cationic intermediates [69]. Hence, we hypothesized that any factor enhancing the rate of the first step by stabilizing carbocations will

Computation-guided scaffold exploration of 2E,6E-1,10-trans/cis-eunicellanes

• Zining Li,
• Sana Jindani,
• Volga Kojasoy,
• Teresa Ortega,
• Erin M. Marshall,
• Khalil A. Abboud,
• Sandra Loesgen,
• Dean J. Tantillo and
• Jeffrey D. Rudolf

Beilstein J. Org. Chem. 2024, 20, 1320–1326, doi:10.3762/bjoc.20.115

• chemically-induced cationic cyclization mechanisms, we performed quantum chemical calculations [mPW1PW91/6–31+G(d/p)/SMD(chloroform)] [13][14][15][16][17][18][19][20] to obtain the relative free energies of the cationic intermediates and transition states that interconvert them, as well as the relative free

• epoxide 9, but the similar reaction with 2 yields gersemienol 8. Isolation yields are provided. (B and C) Results of DFT calculations on the protonation-induced cyclizations of 1 and 2. The energies of the cationic intermediates (italicized values) are not on the same energy scale as for the substrates

Light on the sustainable preparation of aryl-cored dibromides

• Fabrizio Roncaglia,
• Alberto Ughetti,
• Nicola Porcelli,
• Biagio Anderlini,
• Andrea Severini and
• Luca Rigamonti

Beilstein J. Org. Chem. 2024, 20, 1076–1087, doi:10.3762/bjoc.20.95

• follows a different mechanism, producing the ortho and para-bromoarenes through Ar-SE, that involves cationic intermediates. In this case, a catalytic amount of iodine [21][22] or FeCl3 [23] is added to enhance the electrophilicity of bromine. While widely employed and capable of producing reliable

Auxiliary strategy for the general and practical synthesis of diaryliodonium(III) salts with diverse organocarboxylate counterions

• Naoki Miyamoto,
• Daichi Koseki,
• Kohei Sumida,
• Elghareeb E. Elboray,
• Naoko Takenaga,
• Ravi Kumar and
• Toshifumi Dohi

Beilstein J. Org. Chem. 2024, 20, 1020–1028, doi:10.3762/bjoc.20.90

• (TFE, Scheme 2B) [21]. Our group previously reported the synthesis of diaryliodonium(III) salts by combining hypervalent iodine(III) reagents with electron-rich arenes in fluoroalcohol solvents, such as TFE or 1,1,1,3,3,3-hexafluoro-2-propanol [21][22]. These solvents stabilize the cationic

• intermediates in the synthesis of diaryliodonium(III) salts from Koser's reagents or (diacetoxyiodo)arenes. While iodonium salts with TfO−, TsO−, and other counterions are common, the related diaryliodonium carboxylates are more attractive from a cost and safety standpoint. In this work, we present a more

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• ) could be prevented when switching to BCl3 (10 mol %). Interestingly, toluene (94), which is generated as a byproduct of the Grob fragmentation, must react more sluggishly with the generated cationic intermediates compared to chloride, as no alkylations of toluene were reported. In 2017, the Snyder group

• concerning the polar hydrochlorinations the activation energy for an anti-Markovnikov addition is at least by 30 kJ mol−1 higher than for normal addition. Therefore, the formation of the anti-Markovnikov product via purely cationic intermediates is never observed. The only report for the formation of the

Recent developments in the engineered biosynthesis of fungal meroterpenoids

• Zhiyang Quan and
• Takayoshi Awakawa

Beilstein J. Org. Chem. 2024, 20, 578–588, doi:10.3762/bjoc.20.50

• cationic intermediates, leading to the terpenoid structure of each product [6][7]. Particular attention has been paid to the biosynthesis of the compounds derived from farnesyl-DMOA (5) composed of 3,5-dimethylorsellinic acid (DMOA, 4) and the C15 terpenoid moiety due to their structural diversity (Figure

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

• Ruichen Lan,
• Brock Yager,
• Yoonsun Jee,
• Cynthia S. Day and
• Amanda C. Jones

Beilstein J. Org. Chem. 2024, 20, 479–496, doi:10.3762/bjoc.20.43

• protodeaurate alkyl or vinylgold intermediates [29]. HFIP has been shown to facilitate reactions with cationic intermediates and is proposed to activate by promoting formation of hydrogen bonding clusters with a catalyst [63]. Nolan and co-workers have shown that HFIP can be used to activate L–Au–Cl catalysts

Functional characterisation of twelve terpene synthases from actinobacteria

• Anuj K. Chhalodia,
• Houchao Xu,
• Georges B. Tabekoueng,
• Binbin Gu,
• Kizerbo A. Taizoumbe,
• Lukas Lauterbach and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2023, 19, 1386–1398, doi:10.3762/bjoc.19.100

• either through diphosphate abstraction (for type I terpene synthases) or protonation of the substrate (type II terpene synthases). The resulting cationic species can then react in a cascade reaction via a series of cationic intermediates involving cyclisations, hydride or proton shifts, and skeletal

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• the reaction mechanism supported by DFT calculations and concluded that FeF2 plays an important redox role in assisting the cleavage of oxidants and the oxidation of carbon radicals to cationic intermediates of oxygen. CDC reactions between C(sp3)–H/C(sp)–H bonds catalyzed by iron have been reported

• ][132][133][134][135]. Further progress in this field also needs to identify the radical intermediates and some cationic intermediates involved in the catalytic cycle, for which there is currently still some controversy about the actual reaction pathway. Additional mechanistic and theoretical studies

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

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

• . Alternatively, reprotonation of 1 at C-10 can also induce the formation of the guaiane skeleton. Assuming anti addition to the C-4/C-5 double bond in 1, only four cationic intermediates (K1–K4) can be generated by reprotonation at C-4 (Scheme 14A). Similarly, reprotonation of 1 at C-10 leads by anti addition to

• the C-1/C-10 double bond to four cationic intermediates, L1–L4 (Scheme 14B). The guaiane sesquiterpenes derived from cationic intermediates K1, K2 and K4 are summarised in Scheme 15A, while no compounds are known whose formation could be explained from K3. β-Bulnesene (53), a product by the

• [112][113][114][115][116], no enantioselective synthesis is available. Full 1H and 13C NMR data of 53 (including 14 carbon signals) have been published [113]. The guaiane sesquiterpenes that are potentially derived from cationic intermediates L1–L4 are summarised in Scheme 16A. trans-β-Guaiene (54) can

Supramolecular approaches to mediate chemical reactivity

• Pablo Ballester,
• Qi-Qiang Wang and
• Carmine Gaeta

Beilstein J. Org. Chem. 2022, 18, 1463–1465, doi:10.3762/bjoc.18.152

• capsule can catalyze the cyclization of (S)-citronellal forming isopulegol. In this study it was exploited the ability of the resorcinarene capsule to work as a Brønsted acid catalyst, and its aptitude to stabilize cationic intermediates and transition states inside the cavity. Velmurugan, Hu and co

A resorcin[4]arene hexameric capsule as a supramolecular catalyst in elimination and isomerization reactions

• Tommaso Lorenzetto,
• Fabrizio Fabris and
• Alessandro Scarso

Beilstein J. Org. Chem. 2022, 18, 337–349, doi:10.3762/bjoc.18.38

• promoting the protonation of the substrates leading to the formation of cationic intermediates that are stabilized within the cavity with consequent peculiar features in terms of acceleration and product selectivity. In all cases the catalytic activity displayed by the hexameric capsule is remarkable if

• compared to many other strong Brønsted or Lewis acids. Keywords: cationic intermediates; encapsulation; organocatalysis; resorcin[4]arene hexamer; supramolecular catalysis; Introduction In enzymatic catalysis, the substrate is selected matching the size, shape and specific functional groups present in

• cationic intermediates is crucial for the supramolecular catalytic activity observed. In the reactions studied, the capsule plays a crucial role in steering product selectivity, thus further stimulating the investigation of new reactions. Experimental Instrumentation and operating conditions The 1H NMR

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

• bond of these oxadiazoles quantitatively resulted in E/Z-vinyl triflates. The reactions of the cationic intermediates have been studied by DFT calculations and the reaction mechanisms are discussed. Keywords: acetylene-oxadiazoles; Friedel–Crafts reaction; hydroarylation; superelectrophilic activation

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

• fluorine, which helps to generate cations but does not affect cationic reactions [23][24][25][26][27]. Thus, HFIP greatly facilitates reactions via cationic intermediates [28]. In the presence of a catalytic amount of trifluoromethanesulfonic acid in HFIP, (biaryl-2-yl)acetoaldehydes or their acetal

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

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• cyclobutene and several cationic intermediates and mainly yield 2-(1-phenylvinyl)indenes. In a similar reaction cascade, a fulvene derivative was obtained with 1,4-diphenylbutadiene as the substrate. Keywords: alkynes; aromatic substitution; cyclization; cycloaddition; iminium salts; Introduction In recent

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• cationic intermediates underwent hydrolysis during aqueous workup, leading to the observed products. It was assumed that a similar sulfur atom migration should occur in the presence of Brønsted acid under dry conditions. Therefore, a set of phosphine sulfides prepared above was subjected to the reaction

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• ]. As these solutions are heated, they become much darker in color, implying a higher level of protonation. Upon cooling, a more normal color is returned. Full protonation of 13 at 150 °C would explain thermodynamic control by cationic intermediates. Our naïve supposition at the outset of this project

The cyclopropylcarbinyl route to γ-silyl carbocations

• Xavier Creary

Beilstein J. Org. Chem. 2019, 15, 1769–1780, doi:10.3762/bjoc.15.170

• potential rearranged cation 81 (E = CN) is not even an energy minimum, but a transition state. Conclusion 1-Substituted-cis-2-trimethylsilylyclopropylcarbinyl mesylates and triflates 13 solvolyze in CD3CO2D to give products derived from 3-trimethylsilylcyclobutyl cations. These cationic intermediates are

• [12] leaving groups, reacted in aqueous solvents to give an identical mixture of products 3, 4, and 5 (Scheme 1). Additionally, solvolysis rates were far greater than expected for primary and strained secondary systems. To account for these facts, it has been suggested that there are common cationic

• intermediates in these solvolysis reactions of 1 and 2. Labelling [13][14][15], stable ion [16][17][18][19], and computational studies [19] implicate the involvement of three degenerate cyclopropylcarbinyl cations, 6a, 6b, and 6c, in equilibrium with cyclobutyl cation 7, as well as the homoallylic cation 8

Molecular basis for the plasticity of aromatic prenyltransferases in hapalindole biosynthesis

• Takayoshi Awakawa and
• Ikuro Abe

Beilstein J. Org. Chem. 2019, 15, 1545–1551, doi:10.3762/bjoc.15.157

• , and the other PTases, but W119 is conserved or substituted with tyrosine among all of the aligned PTases (Figure 6). The aromatic amino acids around W119 are also important to support the aromatic substrates and cationic intermediates in the X-ray structural studies of CloQ and EpzP [28][30]. The

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• under the action of Brønsted or Lewis acids can be explained by involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates. Strong coordination of Lewis acid AlCl3 with the P=O group completely deactivates it for further intramolecular reactions

Phylogenomic analyses and distribution of terpene synthases among Streptomyces

• Lara Martín-Sánchez,
• Kumar Saurabh Singh,
• Mariana Avalos,
• Gilles P. van Wezel,
• Jeroen S. Dickschat and
• Paolina Garbeva

Beilstein J. Org. Chem. 2019, 15, 1181–1193, doi:10.3762/bjoc.15.115

• substrate 2-methyl-GPP to form 2-MIB (2) [25][26]. An S-adenosylmethionine (SAM) dependent methyl transferase is responsible for the methylation of GPP into 2-methyl-GPP (14, Scheme 2). Its isomerisation to 15 allows for a cyclisation via the cationic intermediates B and C to 2. Genes encoding for SAM

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• were converted into α-allenic tertiary alcohols 22a–c (30–61%) The formation of alcohols 22a–c was explained by a mechanism involving ionization of the C4–O bond in imidates 21a–c, followed by ring opening of the alkylidenecyclopropyl cationic intermediates 23a–c [52] and addition of water to the

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov,
• Olesya V. Khoroshilova and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

• allenes 2. The main goals of this work were the investigation of reactions of sulfur-containing allenes 1 and 2 under electrophilic activation with Brønsted or Lewis (super)acids, and the study on cationic intermediates of these reactions by means of NMR and DFT calculations. Results and Discussion First