Indium-mediated C-allylation of melibiose

• Christian Denner,
• Manuel Gintner,
• Hanspeter Kählig and
• Walther Schmid

Beilstein J. Org. Chem. 2019, 15, 2458–2464, doi:10.3762/bjoc.15.238

• the need for acid catalysis or other promotors [15]. This was also observed in our studies reflected in the significantly higher conversion rates employing indium versus tin (Table 1, entries 1 and 3). With respect to the solvent system, different ratios of an ethanol/water mixture were investigated

Cyclopropanation–ring expansion of 3-chloroindoles with α-halodiazoacetates: novel synthesis of 4-quinolone-3-carboxylic acid and norfloxacin

• Sara Peeters,
• Linn Neerbye Berntsen,
• Pål Rongved and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2019, 15, 2156–2160, doi:10.3762/bjoc.15.212

• conditions without the need for external acid catalysis. These relatively mild reaction conditions should be applicable to a large substrate scope. We anticipated that our novel cyclopropanation–ring expansion reaction would apply to 3-chloroindol derivatives, and designed a simple and straightforward

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• anion; tritylium salt; Introduction Carbocation Lewis acid catalysis has grown significantly over the last two decades [1][2][3][4][5][6][7][8][9][10][11][12][13]. The development of asymmetric carbocation catalysts has been long pursued but remains a challenging task. One strategy is to design and

• investigated in Lewis acid catalysis over the past decades, a chiral counter anion [34][35] with metal elements as the central atom, however, was seldom reported. Typically, the tritylium salts with weakly coordinating anions can be synthesized through a simple halide abstraction from the trityl halide in the

• , Scheme 3a). The electron-rich nature of dimethylanthracene may account for catalysis with the iron salts. On the other hand, an opposite chiral induction in this case is a clear indication of distinctive carbocation catalysis instead of metal Lewis acid catalysis in the presence of trityl chloride. In

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• reaction reported in 1893 comprises the acid–catalyzed condensation of ethyl acetoacetate, benzaldehyde and urea to generate 3,4-dihydropyrimidin-2(1H)-one [41]. From that time, the reaction was extended to Lewis-acid catalysis and the use of other solvents such as methanol or aprotic solvents such as THF

A three-component, Zn(OTf)₂-mediated entry into trisubstituted 2-aminoimidazoles

• Alexei Lukin,
• Anna Bakholdina,
• Anna Kryukova,
• Alexander Sapegin and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2019, 15, 1061–1064, doi:10.3762/bjoc.15.103

• propargylureas (leading to 2-imidazolones) and extend the range of Lewis acid-catalyzed azole syntheses based on N-carbonyl propargylamines. Keywords: alkyne hydroamination; cyclocondensation; Lewis acid catalysis; multicomponent reactions; propargylurea; Introduction The pioneering publications of Beller and

• turned our attention to propargylureas 4. These have been previously converted to the respective 2-imidazolones via base-promoted intramolecular amination of the propargyl group [5][6]. However, such transformations have not been studied under transition metal or Lewis acid catalysis. Moreover, the

Synthesis of a novel category of pseudo-peptides using an Ugi three-component reaction of levulinic acid as bifunctional substrate, amines, and amino acid-based isocyanides

• Maryam Khalesi,
• Azim Ziyaei Halimehjani and
• Jürgen Martens

Beilstein J. Org. Chem. 2019, 15, 852–857, doi:10.3762/bjoc.15.82

• by acid catalysis from renewable resources, such as sugars, lignocellulosic biomass and waste materials [18]. It can be used as a bifunctional precursor for the synthesis of pharmaceuticals, plasticizers, and different additives [19]. Furthermore, it is recognized as an excellent starting material

Tuning the stability of alkoxyisopropyl protection groups

• Zehong Liang,
• Henna Koivikko,
• Mikko Oivanen and
• Petri Heinonen

Beilstein J. Org. Chem. 2019, 15, 746–751, doi:10.3762/bjoc.15.70

• . The vinyl ether hydrolysis has earlier shown to be even a subject of general acid catalysis [13][14]. It is useful to compare the stabilities of the acetal protections to those of the 4,4’-dimethoxytrityl protecting group used in oligonucleotide synthesis. Directly comparable data are hard to find

Cross metathesis-mediated synthesis of hydroxamic acid derivatives

• Shital Kumar Chattopadhyay,
• Subhankar Ghosh and
• Suman Sil

Beilstein J. Org. Chem. 2018, 14, 3070–3075, doi:10.3762/bjoc.14.285

• important demonstration of the protocol is the preparation of the unusual amino acid component of the bioactive cyclic peptide Chap-31. Keywords: α-amino acid; catalysis; cross metathesis; hydroxamates; Introduction Cross-metathesis reactions (CM) have rapidly grown [1][2][3] to be a reliable method for

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• takes place from polyfunctionalized cyclohexanones or related compounds through a Michael reaction [7], successive inter- and intramolecular radical processes [8], intramolecular carbene addition/cyclization [9][10], aldol cyclizations either under Lewis acid catalysis [11] or from diazoketones in the

Functionalization of graphene: does the organic chemistry matter?

• Artur Kasprzak,
• Agnieszka Zuchowska and
• Magdalena Poplawska

Beilstein J. Org. Chem. 2018, 14, 2018–2026, doi:10.3762/bjoc.14.177

• stability [41][42]. Additionally, some researchers have used the acid catalysis [39] or grinding-induced process [40] for the esterification reaction, and the changes in the spectra (e.g., IR, XPS) were not prominent enough to imply the formation of covalent ester-type linkages. In the grinding-induced case

Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

• nucleotide are extensively used in mechanistic studies of protein nucleases and ribozymes. Rate accelerating 3´-bridging substitution has been used to find out whether the chemical step really is rate-liming and 5´-substitution to verify that some small ribozymes utilize general acid catalysis [40]. The

• linkage has undergone rapid initial protonation. In other words, a monoanionic phosphorane is obtained by a specific acid/general base mechanism that is experimentally equivalent to general acid catalysis. The monoanionic phosphorane is stable enough to pseudorotate and may, hence, undergo isomerization

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• indole polyheterocycles 49 and 50 in good yields with 90–99% ee. One of the latest publications around this topic has been reported by Deb et al. [86][87]. Various 2-(aminoalkyl)phenols or 1-(aminoalkyl)naphthols 51 were reacted with indoles under Brønsted acid catalysis resulting in 3-(α,α-diarylmethyl

From dipivaloylketene to tetraoxaadamantanes

• Gert Kollenz and
• Curt Wentrup

Beilstein J. Org. Chem. 2018, 14, 1–10, doi:10.3762/bjoc.14.1

• need for acid catalysis. As in the case of the addition of arylamines, monodecarboxylation takes place, and in the presence of a strong acid, they are converted to the tetraoxaadamantanes 28 and 29 (65–93%) [35]. Several bisdioxine derivatives of aromatic di- and triamines as well as crown-ether

Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols

• Katrina Tait,
• Alysia Horvath,
• Nicolas Blanchard and
• William Tam

Beilstein J. Org. Chem. 2017, 13, 2888–2894, doi:10.3762/bjoc.13.281

• reactions. The scope of the reaction was successfully expanded to include primary, secondary, and tertiary alcohol nucleophiles. Through X-ray crystallography, the stereochemistry of the product was determined which confirmed an SN2-like mechanism to form the ring-opened product. Keywords: acid catalysis

Synthesis of 2-aminosuberic acid derivatives as components of some histone deacetylase inhibiting cyclic tetrapeptides

• Shital Kumar Chattopadhyay,
• Suman Sil and
• Jyoti Prasad Mukherjee

Beilstein J. Org. Chem. 2017, 13, 2153–2156, doi:10.3762/bjoc.13.214

• and the synthesis of peptides of biological relevance. Keywords: α-amino acid; catalysis; chiral pool; cross metathesis; cyclic peptides; Introduction α-Aminosuberic acid (Asu) is a component of apicidin F (1, Figure 1) belonging to an interesting class of cyclic tetrapeptides displaying

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

• Pavel Nagorny and
• Zhankui Sun

Beilstein J. Org. Chem. 2016, 12, 2834–2848, doi:10.3762/bjoc.12.283

• reactive complex with the LUMO. These results are further backed up by control experiments demonstrating that catalytic quantities of hydroiodic acid were less effective in promoting this reaction than molecular iodine, and hidden Brønsted acid catalysis is unlikely to be operational in these studies. In

• after 24 h. Remarkably, when the catalyst loading was reduced to 1 mol %, the product could still be obtained in 69% yield after 96 h. Although the hidden acid catalysis due to the trace amounts of HI was not ruled out, the proposed N-halogen bond formation between quinolone and perfluoroiododecane

• out hidden acid catalysis due to the formation of trace quantities of HBr through hydrolysis of the substrate. To further enhance the reactivity of the halogen bond donors, Huber and colleagues later designed 5-iodo-1,2,3-triazolium-based multidentate salts L18 [83][84]. Triazolium salts L18 were

O-Alkylated heavy atom carbohydrate probes for protein X-ray crystallography: Studies towards the synthesis of methyl 2-O-methyl-L-selenofucopyranoside

• Roman Sommer,
• Dirk Hauck,
• Annabelle Varrot,
• Anne Imberty,
• Markus Künzler and
• Alexander Titz

Beilstein J. Org. Chem. 2016, 12, 2828–2833, doi:10.3762/bjoc.12.282

• introduction of the methylseleno moiety was performed by nucleophilic substitution of the α-bromide in 5 with methylselenol obtained by in situ reduction of dimethyl diselenide with NaBH4 [23]. The obtained crude methyl β-selenofucoside was anomerized under Lewis acid catalysis to give the anomeric mixture in

Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols

• Katrina Tait,
• Oday Alrifai,
• Rebecca Boutin,
• Jamie Haner and
• William Tam

Beilstein J. Org. Chem. 2016, 12, 2189–2196, doi:10.3762/bjoc.12.209

• , the dihydronaphthalenols can fully aromatize to form various substituted naphthalene derivatives 11. This has been accomplished through acid catalysis with various alcohol nucleophiles [31]. The last type of predicted ring opening (type 3) which has not yet been observed involves the attack of the

Silica-supported sulfonic acids as recyclable catalyst for esterification of levulinic acid with stoichiometric amounts of alcohols

• Raimondo Maggi,
• N. Raveendran Shiju,
• Veronica Santacroce,
• Giovanni Maestri,
• Franca Bigi and
• Gadi Rothenberg

Beilstein J. Org. Chem. 2016, 12, 2173–2180, doi:10.3762/bjoc.12.207

• of our interest in acid catalysis [36][37][38], we prepared a set of solid materials for the esterification of levulinic acid. Upon preliminary screening, supported sulfonic acids seemed promising candidates. They were prepared following a reported procedure by the tethering method [39], which

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

• Maurizio Selva,
• Alvise Perosa,
• Sandro Guidi and
• Lisa Cattelan

Beilstein J. Org. Chem. 2016, 12, 1911–1924, doi:10.3762/bjoc.12.181

• organic carbonates by ionic-liquid catalysis goes back approximately five years. Both acidic and basic ionic liquids were employed as catalysts for the pursuit of this scope. The following section is divided into two topics: the first focuses on basic catalysis, and the second on acid catalysis. Basic

• -methylimidazolium chloride as the catalyst (Figure 4). With a 10 mol % ionic liquid loading, the transesterification reaction of DMC with eighteen different alcohols ROH yielded the desired unsymmetrical carbonates (Figure 4) under mild reaction conditions (80 °C, DMC:ROH in 1:1 ratio) [69]. Acid catalysis: In the

The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals

• Sonia L. Repetto,
• James F. Costello,
• Craig P. Butts,
• Joseph K. W. Lam and
• Norman M. Ratcliffe

Beilstein J. Org. Chem. 2016, 12, 1467–1475, doi:10.3762/bjoc.12.143

• -breaking work on acid catalysis [4], to more recent investigations as models for glycosidic bond cleavage [5], orthoesters have been examined using a range of methods, solvents (i.e., water, methanol, dioxane, and mixtures thereof), and conditions [6][7]. It has been difficult to draw upon this disparate

• rate constants (kobs) were determined using the rate equation integrated over time, using 1H NMR spectroscopy to evaluate relative concentrations at 25 ± 0.5 °C. Having already established [1] that specific acid catalysis is more likely to be the dominant mechanism operating in jet fuel/water mixtures

Synergistic chiral iminium and palladium catalysis: Highly regio- and enantioselective [3 + 2] annulation reaction of 2-vinylcyclopropanes with enals

• Haipan Zhu,
• Peile Du,
• Jianjun Li,
• Ziyang Liao,
• Guohua Liu,
• Hao Li and
• Wei Wang

Beilstein J. Org. Chem. 2016, 12, 1340–1347, doi:10.3762/bjoc.12.127

• bond and sterically blocks the attack of the C=N iminium ion functionality posed by the bulky amine catalyst. In parallel, a LA promotes to open the D–A cyclopropanes 2. The cooperative activation of two independent substrates by respective iminium and Lewis acid catalysis may enable an unprecedented

Art, auto-mechanics, and supramolecular chemistry. A merging of hobbies and career

• Eric V. Anslyn

Beilstein J. Org. Chem. 2016, 12, 362–376, doi:10.3762/bjoc.12.40

• synthetic receptors we created were designed to answer basic science questions about enzyme mechanisms [19][47], rate enhancements from ion-pairing and general acid-catalysis [48], as well as reveal the strengths of hydrogen bonding. Interspersed among this work using synthetic receptors there was a

Synthesis and biological evaluation of a novel MUC1 glycopeptide conjugate vaccine candidate comprising a 4’-deoxy-4’-fluoro-Thomsen–Friedenreich epitope

• Manuel Johannes,
• Maximilian Reindl,
• Bastian Gerlitzki,
• Edgar Schmitt and
• Anja Hoffmann-Röder

Beilstein J. Org. Chem. 2015, 11, 155–161, doi:10.3762/bjoc.11.15

• ’-fluoro-TF SPPS building block 11 started by conversion of peracetylated D-glucose 1 into β-thio-glycoside 2 [45][46] under Lewis acid catalysis in 81% yield (Scheme 1). Subsequent Zemplén deacetylation [47], followed by 4,6-benzylidene acetal formation and acetylation provided fully protected precursor 3

Facile synthesis of 1H-imidazo[1,2-b]pyrazoles via a sequential one-pot synthetic approach

• András Demjén,
• Márió Gyuris,
• János Wölfling,
• László G. Puskás and
• Iván Kanizsai

Beilstein J. Org. Chem. 2014, 10, 2338–2344, doi:10.3762/bjoc.10.243

• on Lewis acid catalysis, though better results were obtained by using a catalytic amount of TFA in EtOH (Table 1, entries 5–7). From the aspect of an operationally simple green protocol, a mixture of water and EtOH as reaction medium yielded optimum results in terms of isolated yield, reaction time