Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• [58] makes BIFOL (5) a potentially promising chiral backbone for new organo silicates, e.g., silanediol 9 (Figure 1). As a silicic acid ester, silanediol 9 should show increased acidity in comparison to C–Si(OH)2 derivates, e.g., 1–4 [40]. In this work the syntheses of BIFOXSiCl2 (7), BIFOXSi(OH)2 (9

• reported silanediol derivatives 2a and 2b [43], an increase of acidity of one outward facing OH group is achieved by intermolecular hydrogen bonds [43]. Chloride binding The X-ray crystal structures of chlorosilanol 8 (Figure 17) and silanediol 9 (Figure 16) with co-crystallized acetone indicate the

MoO₃ on zeolites MCM-22, MCM-56 and 2D-MFI as catalysts for 1-octene metathesis

• Hynek Balcar,
• Martin Kubů,
• Naděžda Žilková and
• Mariya Shamzhy

Beilstein J. Org. Chem. 2018, 14, 2931–2939, doi:10.3762/bjoc.14.272

• ‘ acidity and accessibility of the catalytic species on the surface. On the other hand the supports‘ acidity decreases the selectivity to the main metathesis product C14 due to an acid-catalyzed double bond isomerization (followed by cross metathesis) and oligomerization. 6MoO3/2D-MFI(26) with a lower

• metathesis catalysts [1]. Albeit typical ill-defined catalysts they are still popular as relatively cheap catalysts finding industrial applications especially in the treatment of low olefins [2][3][4][5]. Their catalytic activity depends on many factors, especially on Mo loading, support acidity, and pre

• ) where MoO3 signals were clearly visible, probably as a result of lower external surface area. Contrary to the all-siliceous mesoporous sieves (like SBA-15) which are neutral, zeolites are acidic and their acidity (both Brønsted and Lewis-type) plays an important role for catalysis. The acid site

An overview on recent advances in the synthesis of sulfonated organic materials, sulfonated silica materials, and sulfonated carbon materials and their catalytic applications in chemical processes

• Hashem Sharghi,
• Pezhman Shiri and
• Mahdi Aberi

Beilstein J. Org. Chem. 2018, 14, 2745–2770, doi:10.3762/bjoc.14.253

• substance and chlorosulfonic acid for the first time. The authors proposed that the high Brønsted acidity of the catalyst arises mainly from hydrogen bonds between the two -SO3H groups. The catalyst 53 was studied by different analyses including FTIR, 1H NMR, 13C NMR, UV–vis, and fluorescence spectra. Then

Synthesis of functionalised β-keto amides by aminoacylation/domino fragmentation of β-enamino amides

• Pavel Yanev and
• Plamen Angelov

Beilstein J. Org. Chem. 2018, 14, 2602–2606, doi:10.3762/bjoc.14.238

• enolates is one of the main synthetic approaches towards β-keto amides and has found numerous applications [1][2][3][4][5][6][7][8][9]. However, while the generation of tertiary amide enolates is straightforward, this is not the case with secondary and primary amides. The NH acidity of the latter compounds

Synergistic electrodeposition of bilayer films and analysis by Raman spectroscopy

• Saadeldin E. T. Elmasly,
• Luca Guerrini,
• Joseph Cameron,
• Alexander L. Kanibolotsky,
• Neil J. Findlay,
• Karen Faulds and
• Peter J. Skabara

Beilstein J. Org. Chem. 2018, 14, 2186–2189, doi:10.3762/bjoc.14.191

• two layers. Successful PEDOT/PEDTT bilayer formation has been confirmed by Raman spectroscopy. Electrodeposition of the bilayer has advantages over traditional processing methods including avoiding the acidity of PSS which is detrimental to the lifetime of devices containing PEDOT:PSS [18] and the

Host–guest complexes of conformationally flexible C-hexyl-2-bromoresorcinarene and aromatic N-oxides: solid-state, solution and computational studies

• Rakesh Puttreddy,
• Ngong Kodiah Beyeh,
• S. Maryamdokht Taimoory,
• Daniel Meister,
• John F. Trant and
• Kari Rissanen

Beilstein J. Org. Chem. 2018, 14, 1723–1733, doi:10.3762/bjoc.14.146

• -acidity of aromatic protons assist in orienting the N-oxide guest by C–H···π interactions, and that the HB accepting N–O group is positioned “up”, extending out beyond the cavity to interact with solvent molecules. Our work, investigating the interactions of PyNO guests with various resorcinarene hosts

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• reasonable yields over shorter reaction times and at low catalyst loading. The regioselectivity of the reactions was strongly dependent on the acidity or basicity of the reaction conditions. Under acidic conditions, nucleophilic attack of the thiol at the more-substituted α-carbon was favored while under

Heterogeneous acidic catalysts for the tetrahydropyranylation of alcohols and phenols in green ethereal solvents

• Ugo Azzena,
• Massimo Carraro,
• Gloria Modugno,
• Luisa Pisano and
• Luigi Urtis

Beilstein J. Org. Chem. 2018, 14, 1655–1659, doi:10.3762/bjoc.14.141

• , i.e., NH4Cl, NH4Br and NH4H2PO4 (Table 1, entries 1–4). On the other hand, inorganic salts with a relatively higher acidity, i.e., NH4HSO4, NaHSO4 and KHSO4 [31], as well as Amberlyst 15 and Montmorillonite K10, efficiently promoted practically quantitative conversion of the starting material into the

Anomeric modification of carbohydrates using the Mitsunobu reaction

• Julia Hain,
• Patrick Rollin,
• Werner Klaffke and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2018, 14, 1619–1636, doi:10.3762/bjoc.14.138

• , some other NH acids, and thiols. The standard azo reagents used are diethyl- (DEAD) or diisopropyl- (DIAD) azodicarboxylate. However, alternative reagents such as azodicarboxamides [15][16] or stabilized phosphoranes were also developed to allow reaction with nucleophiles of weaker acidity. The typical

• acyloxyphosphonium ion. This in turn reacts with the anomeric oxyanion to furnish the anomerically modified sugar with retention of configuration via anomeric O-alkylation. This mechanistic proposal is in agreement with observations by Lubineau et al., who could correlate the acidity of the employed nucleophile with

• authors state that the observed pKa effect is either due to the influence of the acidity of the employed acid on the reaction mechanism or results from the proton-catalyzed change of the anomeric ratio of the starting material 30 in solution. Very recently, anomeric phosphorylation via a Mitsunobu

Glycosylation reactions mediated by hypervalent iodine: application to the synthesis of nucleosides and carbohydrates

• Yuichi Yoshimura,
• Hideaki Wakamatsu,
• Yoshihiro Natori,
• Yukako Saito and
• Noriaki Minakawa

Beilstein J. Org. Chem. 2018, 14, 1595–1618, doi:10.3762/bjoc.14.137

• iodine-mediated glycosylation to purine 4’-thionucleosides [46]. However, the reaction of 36 with 6-chloropurine resulted in the formation of a regioisomer reacting at the 4-position without any formation of the desired purine 4’-thionucleoside. The result should relate to the acidity of the α hydrogen

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• respectively have been designed by Yilmaz et al. as shown in Figure 9 [65]. A new prolinamide derivative 92 with increased NH acidity has been synthesized from diformylcalixarene derivative 90 as shown in Scheme 24 [66]. Aldol reaction between 21 and 70 in water showed that catalyst 75 provided faster reaction

A selective removal of the secondary hydroxy group from ortho-dithioacetal-substituted diarylmethanols

• Anna Czarnecka,
• Emilia Kowalska,
• Agnieszka Bodzioch,
• Joanna Skalik,
• Marek Koprowski,
• Krzysztof Owsianik and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2018, 14, 1229–1237, doi:10.3762/bjoc.14.105

• , ether cleavage and dehalogenation (I but not Cl and Br) are common, side reactions due to either the high acidity which is necessary to generate carbocationic species or due to the use of strongly reducing reaction conditions [28][29][30][46][47][48][49][50][51][52]. In this context, a serious challenge

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

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

• occurrence of the proton transfer as part of the rate limiting step may be evaluated by altering the acidity of the proton donor (or acceptor). Plotting of log k against the pKa of the proton donor (or acceptor) gives the Brönsted α (β for the acceptor) that refers to the extent of proton transfer in the

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• , an increased acidity of the ortho position of the fluorine atom could have also contributed to the observed regioselectivity [31]. Curiously, the reaction of 2-naphthylimine resulted in the preferential alkenylation of the more hindered 1-position rather than the 3-position, with a regioselectivity

An alternative to hydrogenation processes. Electrocatalytic hydrogenation of benzophenone

• Cristina Mozo Mulero,
• Alfonso Sáez,
• Jesús Iniesta and
• Vicente Montiel

Beilstein J. Org. Chem. 2018, 14, 537–546, doi:10.3762/bjoc.14.40

• v/v) and 0.1 M H2SO4, or (ii) 0.5 M benzophenone in ethanol 96% /water (90:10 v/v) in the absence of the sulfuric acid electrolyte in order to explore the influence of the medium acidity upon the electrochemical hydrogenation. A peristaltic pump Ismatel Reglo DIG MS/CA 2–8 provided a catholyte flow

Aminomethylation/hydrogenolysis as an alternative to direct methylation of metalated isoquinolines – a novel total synthesis of the alkaloid 7-hydroxy-6-methoxy-1-methylisoquinoline

• Benedikt C. Melzer,
• Jan G. Felber and
• Franz Bracher

Beilstein J. Org. Chem. 2018, 14, 130–134, doi:10.3762/bjoc.14.8

• , due to its intrinsic C–H acidity, open opportunities for further functionalization. Since most isoquinoline alkaloids bear hydroxy and/or methoxy substituents at the positions 6 and 7, we regarded 7-hydroxy-6-methoxy-1-methylisoquinoline (1) as well as analogues containing a protected 7-hydroxy group

Halogen-containing thiazole orange analogues – new fluorogenic DNA stains

• Aleksey A. Vasilev,
• Meglena I. Kandinska,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• David Sucunza,
• Juan J. Vaquero,
• Obis D. Castaño,
• Stanislav Baluschev and
• Silvia E. Angelova

Beilstein J. Org. Chem. 2017, 13, 2902–2914, doi:10.3762/bjoc.13.283

• for the success of the reaction because of the CH-acidity of the benzyl fragment, which otherwise leads to the possibility of side reactions if trimethylamine or other less hindered basic reagents are employed. Photophysical properties Absorption The longest wavelength absorption maxima of the studied

Position-dependent impact of hexafluoroleucine and trifluoroisoleucine on protease digestion

• Susanne Huhmann,
• Anne-Katrin Stegemann,
• Kristin Folmert,
• Damian Klemczak,
• Johann Moschner,
• Michelle Kube and
• Beate Koksch

Beilstein J. Org. Chem. 2017, 13, 2869–2882, doi:10.3762/bjoc.13.279

• strong, short C–F bonds and perturb the acidity and basicity of adjacent functional groups. Moreover, these changes may strongly influence hydrogen bonding and electrostatic interactions that are crucial for binding to receptors or, in context of protease stability, enzymes. Thus, when introduced in the

What contributes to an effective mannose recognition domain?

• Christoph P. Sager,
• Deniz Eriş,
• Martin Smieško,
• Rachel Hevey and
• Beat Ernst

Beilstein J. Org. Chem. 2017, 13, 2584–2595, doi:10.3762/bjoc.13.255

• to gain enthalpy, and thereby increase affinity. UPEC perfects this approach with the calcium-devoid binding site of FimHLD (I). A possible explanation for the lack of a calcium ion in the FimH binding site may relate to the slight acidity of urine (pH 5.5–7.0), with a calcium clearance of 20–300 mg

Hydrolysis, polarity, and conformational impact of C-terminal partially fluorinated ethyl esters in peptide models

• Vladimir Kubyshkin and
• Nediljko Budisa

Beilstein J. Org. Chem. 2017, 13, 2442–2457, doi:10.3762/bjoc.13.241

• limited the substrate scope. Nonetheless, due to the high acidity of the C-terminal carboxylic group [50], a number of C-terminally modified peptides were readily prepared by this method with full conversion. The availability of the C-terminal 2,2-difluoroethanol-esterified peptides also enables the

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• % [21]. Synthesis of propargylamines containing electron-withdrawing substituents Aromatic and carbonyl substituents in the Cβ-position of propargylamines (occurring in analogoues of the amino acids phenylalanine, tyrosine, histidine, tryptophan, aspartic acid and asparagine) increase the acidity of the

• adjacent protons considerably. In the precursor sulfinylimines 5 of the target propargylamines the acidity of the protons of the methylene moiety is further increased by the electron-withdrawing effect of the adjacent sulfinyl imino moiety. Thus, the nucleophilic addition of (trimethylsilyl)ethynyllithium

• additionally increase the acidity of the α-proton. Nevertheless, glycine derivatives with electron-withdrawing substituents like formylglycine [58][59], phenylglycine [60][61] and fluorinated alanine [62][63][64] have attracted great attention as peptidomimetics, drugs or in the bioorthogonal functionalization

Electron-deficient pyridinium salts/thiourea cooperative catalyzed O-glycosylation via activation of O-glycosyl trichloroacetimidate donors

• Mukta Shaw,
• Yogesh Kumar,
• Rima Thakur and
• Amit Kumar

Beilstein J. Org. Chem. 2017, 13, 2385–2395, doi:10.3762/bjoc.13.236

• trichloroacetimidate donors using a synergistic catalytic system of electron-deficient pyridinium salts/aryl thiourea derivatives at room temperature is demonstrated. The acidity of the adduct formed by the 1,2-addition of alcohol to the electron-deficient pyridinium salt is increased in the presence of an aryl

• presence of Schreiner′s thiourea in the reaction medium enhances the acidity of the ammonium salt due to doubling their dual hydrogen bonding ability with the carboxylate and the alkoxy group of the ammonium salt. A thiourea derivative also enhances the nucleophilicity of the glycosyl acceptor by imparting

• to lower acidity of the ammonium salt formed by 1,2-addition of the acceptor to the pyridinium salt. The conjugate base formed after the release of a proton from the ammonium salt may be quite stable to impart a negative charge to the acceptor oxygen. The acidity of the ammonium salt may be enhanced

Synthesis and application of trifluoroethoxy-substituted phthalocyanines and subphthalocyanines

• Satoru Mori and
• Norio Shibata

Beilstein J. Org. Chem. 2017, 13, 2273–2296, doi:10.3762/bjoc.13.224

• sensors [51]. Due to the strong electronegativity of fluorine, the acidity of these pyrrole rings is increased in TFEO-H2Pc. For this reason, it is susceptible to deprotonation, whereas protonation hardly occurs. Trifluoroethoxy-substituted nickel phthalocyanine (TFEO-NiPc) and trifluoroethoxy-substituted

Phosphonic acid: preparation and applications

• Charlotte M. Sevrain,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2017, 13, 2186–2213, doi:10.3762/bjoc.13.219

• first pKa ranging from 1.1 to 2.3 and the second acidity which features a pKa ranging from 5.3 to 7.2 [11]. The values strongly depend on the electronic properties induced by the substituent R. It must be noted that due to the high polarity of the phosphonic acid function, the purification of phosphonic

• phosphonic acid from phosphonates without the need of intense purification in the final step. Indeed, the purification is limited to remove the solvent and volatile reagents that are frequently used in excess (see section 3). Due to the acidity of phosphonic acid this function is deprotonated in water and

• analogue) [11]. Meanwhile, the phosphonic acid derivatives are more acidic when compared to their carboxylic acid equivalents (1.9 to 2.9 units of pKa below for the first acidity of phosphonic acid derivatives) [11]. This property was used to design Brönsted acid catalysts that were used for the