Interactions between photoacidic 3-hydroxynaphtho[1,2-b]quinolizinium and cucurbit[7]uril: Influence on acidity in the ground and excited state

• Jonas Becher,
• Daria V. Berdnikova,
• Darinka Dzubiel,
• Heiko Ihmels and
• Phil M. Pithan

Beilstein J. Org. Chem. 2017, 13, 203–212, doi:10.3762/bjoc.13.23

• red-shifted absorption bands and causes a dual emisson, i.e., a combination of emission bands of the hydroxyquinolizinium and its deprotonated form. Whereas this compound is a weak acid in the ground state (pKa = 7.9), it has a strongly increased acidity in the excited state (pKa* = 0.4). As a result

• acidity or basicity. In fact, it was shown that the pKa of organic acids and bases often shifts by orders of magnitude upon association with CB[n] [16][17][18][19][20][21][22][23][24], which may be used, e.g., to modify catalytic activity [6] or for sensing purposes [7]. Notably, the same effect was

• observed for the excited-state proton transfer (ESPT) of so-called photoacids. The latter are weak acids in the ground state, whereas their acidity in the excited state increases significantly [25][26][27]. As the activity of photoacids is triggered by light, they have a great potential to be employed as

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

• substantial dipole moment (≈4.5 D) almost aligned with the C5–H bond and the relatively high acidity of this position (pKa(DMSO) = 27–28, for the 1H-tautomer). These heterocycles, which are easily available from 1,3-cycloaddition of alkynes and azides, can both form strong C–H bonds with hydrogen bond

Copper-catalyzed asymmetric sp³ C–H arylation of tetrahydroisoquinoline mediated by a visible light photoredox catalyst

• Pierre Querard,
• Inna Perepichka,
• Eli Zysman-Colman and
• Chao-Jun Li

Beilstein J. Org. Chem. 2016, 12, 2636–2643, doi:10.3762/bjoc.12.260

• -arylated PyBox L2 gave very good er under our reaction conditions (Table 2, entry 2). It is noteworthy that the er observed was higher when copper(I) bromide was used as a co–catalyst, compared to copper(II) bromide (Table 2, entry 3), possibly due to the Lewis acidity difference of Cu(I) and Cu(II

Construction of bis-, tris- and tetrahydrazones by addition of azoalkenes to amines and ammonia

• Artem N. Semakin,
• Aleksandr O. Kokuev,
• Yulia V. Nelyubina,
• Alexey Yu. Sukhorukov,
• Petr A. Zhmurov,
• Sema L. Ioffe and
• Vladimir A. Tartakovsky

Beilstein J. Org. Chem. 2016, 12, 2471–2477, doi:10.3762/bjoc.12.241

• hydrazones with starting hydrazide [51]. The presence of acetic acid and mild reaction conditions (0 °C) was essential for the synthesis of hydrazones 1c and 1d (R1 = CH3, R2 = CH3 or (CH2)6CH3), probably because of the their enhanced NH-acidity. Reaction of α-halogen hydrazones 1 with benzylamine In our

Et₃B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

• Ahlem Abidi,
• Yosra Oueslati and
• Farhat Rezgui

Beilstein J. Org. Chem. 2016, 12, 2402–2409, doi:10.3762/bjoc.12.234

• acidity is relatively higher, led to a mixture of the mono- and bis-alkylation products 3c and 4c in 45 and 23% yields, respectively (Table 2, entries 1–3). Under the same conditions, the allylation of a variety of β-keto esters and β-diketones (Table 2, entries 4–9), in DMF at 80 °C, selectively gave the

Isosorbide and dimethyl carbonate: a green match

• Fabio Aricò and
• Pietro Tundo

Beilstein J. Org. Chem. 2016, 12, 2256–2266, doi:10.3762/bjoc.12.218

• bisphenol A in polycarbonate preparation. In this view, the main issue that limits the exploitation of this compound is its lower acidity. To overcome this problem, polycarbonates incorporating an isosorbide moiety have been synthesized via a chlorine-based approach, i.e., employing phosgene or its

Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

• Ángel Cantín,
• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188, doi:10.3762/bjoc.12.208

• 1.9 nm (ITQ-37) [36] have also been tested. These are aluminosilicogermanates that, as the previously tested Al-zeolites or the Al-MCM-41 material, present Brønsted acidity. Interestingly, the pore diameters of ITQ-33, and more so ITQ-37 are close to the pore of the mesoporous MCM-41 presented above

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

• toluene (120 mL) and the resulting supported propylmercaptane has been oxidized to propanesulfonic acid by treatment with 30% aq H2O2 (100 mL; 1 mol) for 24 h under stirring at rt, adding a few drops of concentrated sulfuric acid after 12 h. Acidity has been measured via the titration method [35] (0.51

• . Acidity has been measured via the titration method [35] (0.65 mmol H+/g). SiO2-(CH2)3-O-C6H4-SO3H: A mixture of amorphous silica gel (2.0 g) and bromopropyltrimethoxysilane (0.76 mL, 4.0 mmol) was refluxed in toluene (80 mL) under stirring for 24 hours. The resulting silica supported 3-bromopropane was

• ). Acidity has been measured via titration method [35] (0.73 mmol H+/g). Esterification reaction Levulinic acid, pentanol and the heterogeneous catalyst were stirred for 24 hours in a batch reactor under air. The acid/alcohol ratio, the reaction temperature and the amount of the catalyst were modified as

Superelectrophilic activation of 5-hydroxymethylfurfural and 2,5-diformylfuran: organic synthesis based on biomass-derived products

• Dmitry S. Ryabukhin,
• Dmitry N. Zakusilo,
• Mikhail O. Kompanets,
• Anton A.Tarakanov,
• Irina A. Boyarskaya,
• Tatiana O. Artamonova,
• Mikhail A. Khohodorkovskiy,
• Iosyp O. Opeida and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2016, 12, 2125–2135, doi:10.3762/bjoc.12.202

• strong Lewis acids (AlX3, X = Cl, Br) by their coordination with basic centers of organic compounds, or with acidic zeolites, possessing both Brønsted and Lewis acidity [33]. The main goal of this work was a study of reactions of 5-HMF and 2,5-DFF with arenes under electrophilic activation with Brønsted

• products. It is interesting to note that compounds 4 were not observed in reactions with zeolite (Table 4, entries 3, 10, 14 and 17), most likely, due to lower acidity of the zeolite compared to TfOH and spatial restrictions in zeolite cages, diminishing the contact between protonated aldehyde groups and

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

• be recovered and reused to allow quantitative conversions even after several recycles. Moreover, the study highlighted that the catalytic activity increased with increasing acidity of the ILs and particularly with cations bearing SO3H anions (Scheme 5: ILs I, II, III, and IV). The same imidazolium

• transesterification reaction of dimethyl carbonate with phenol to methyl phenyl carbonate (MPC) and diphenyl carbonate (DPhC), Deshmukh et al. studied dibutyltin oxide as a catalyst in conjunction with Brønsted and Lewis acidic ionic liquids [70]. The authors investigated the relative Lewis and Brønsted acidity of

Dinuclear thiazolylidene copper complex as highly active catalyst for azid–alkyne cycloadditions

• Anne L. Schöffler,
• Ata Makarem,
• Frank Rominger and
• Bernd F. Straub

Beilstein J. Org. Chem. 2016, 12, 1566–1572, doi:10.3762/bjoc.12.151

• copper(I) acetate and sodium acetate as additional base in order to deprotonate the thiazolium salt 1b and to form the bisthiazolylidene copper(I) complex 2. Due to the relatively high acidity of the thiazolium precursor (pKa ≈ 18 [44]), a weak base such as sodium acetate yields small equilibrium

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• developed organocatalytic conjugate addition–enantioselective protonations of α,β-unsaturated imides using thiols. Thiols are attractive nucleophiles due to their acidity, which facilitates deprotonation by amine bases and also reduces undesired competitive deprotonation and epimerization of the enolizable

Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(−)-myrtenol nitrate

• Sean P. Bew,
• Glyn D. Hiatt-Gipson,
• Graham P. Mills and
• Claire E. Reeves

Beilstein J. Org. Chem. 2016, 12, 1081–1095, doi:10.3762/bjoc.12.103

• %, interestingly the concentration of organic nitrates was found to be highly dependent on the relative humidity and seed aerosol acidity. Worthy of note this report also highlighted that “unfortunately, standards are unavailable for the expected organic nitrate products (derived from α-pinene)“ this, again

Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies

• Takashi Nishikata,
• Alexander R. Abela,
• Shenlin Huang and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2016, 12, 1040–1064, doi:10.3762/bjoc.12.99

• their Lewis acidity. Cationic palladium complexes [123], in particular, possess a wide breadth of reactivity, having been used to catalyze Diels–Alder [124][125], aldol and Mannich reactions [126][127][128], Wacker oxidations [129], polymerizations of alkenes [130][131], and asymmetric 1,4-additions

• acidity of the metal center. This is a noteworthy advantage associated with the use of cationic palladium(II) catalysts. Finally, BQ oxidizes the Pd(0) that is reductively eliminated from the HPd(II)+BF4− formed to regenerate the active cationic palladium species Pd2+(BF4)2−. C–H boronic acid coupling

Reactions of N,3-diarylpropiolamides with arenes under superelectrophilic activation: synthesis of 4,4-diaryl-3,4-dihydroquinolin-2(1H)-ones and their derivatives

• Larisa Yu. Gurskaya,
• Diana S. Belyanskaya,
• Dmitry S. Ryabukhin,
• Denis I. Nilov,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2016, 12, 950–956, doi:10.3762/bjoc.12.93

• target products 2 are 44–98% (see Table 1). Also this reaction may be carried out under the action of other acids, e.g., TfOH–SbF5 or AlX3 (X = Cl, Br). But in the stronger acidic system TfOH–SbF5 (Hammet acidity function H0 −19, see [18]) the yields of compounds 2 were usually lower as compared to TfOH

Synthesis and fluorosolvatochromism of 3-arylnaphtho[1,2-b]quinolizinium derivatives

• Phil M. Pithan,
• David Decker,
• Manlio Sutero Sardo,
• Giampietro Viola and
• Heiko Ihmels

Beilstein J. Org. Chem. 2016, 12, 854–862, doi:10.3762/bjoc.12.84

• , the Taft parameter π*, the dipole moment, μ, the acidity, SA, the basicity, SB, the dipolarity and polarizability SPP, the polarizability, SP, or the dipolarity SDP (cf. Supporting Information File 1). In all cases, the plots of the solvent parameters versus the emission energy do not disclose an

Scope and mechanism of the highly stereoselective metal-mediated domino aldol reactions of enolates with aldehydes

• M. Emin Cinar,
• Bernward Engelen,
• Martin Panthöfer,
• Hans-Jörg Deiseroth,
• Jens Schlirf and
• Michael Schmittel

Beilstein J. Org. Chem. 2016, 12, 813–824, doi:10.3762/bjoc.12.80

• center: it should (a) exhibit Lewis acidity, (b) be sufficiently electropositive, and (c) display a sufficiently large ion radius so that the reaction cascade can take place in the periphery of the metal. The latter requirement is apparently prohibitive for a boron(III)-mediated reaction because the ion

cis–trans-Amide isomerism of the 3,4-dehydroproline residue, the ‘unpuckered’ proline

• Vladimir Kubyshkin and
• Nediljko Budisa

Beilstein J. Org. Chem. 2016, 12, 589–593, doi:10.3762/bjoc.12.57

• acidity was depressed with both the 3,4-double bond and 4-CF3 substitutions, the former had a stronger impact. Thus it is evident that the 3,4-double bond significantly increases the electrophilicity of the carbonyl group of the amino acid residue. The effect on the s-trans/s-cis equilibrium was revealed

• electrophilicity of the terminal carbonyl groups (as seen previously in Ac-Xaa acidity) does not have a significant impact on the intramolecular interaction between the two carbonyl groups (as seen from Ks-trans/s-cis values). Similarly, Jenkins et al. reported on bicyclic proline analogues and demonstrated that

The aminoindanol core as a key scaffold in bifunctional organocatalysts

• Isaac G. Sonsona,
• Eugenia Marqués-López and
• Raquel P. Herrera

Beilstein J. Org. Chem. 2016, 12, 505–523, doi:10.3762/bjoc.12.50

• mentioned TS1, where the external acid (AH) would only coordinate to the thiourea moiety enhancing its acidity and thus forming a more active catalytic species (Figure 4). Since the pioneering aminoindanol-containing organocatalyst 4, reported in 2005 [18], other research groups have studied the possibility

• of incorporating this scaffold into diverse organocatalysts. In 2008, Seidel’s group published a new example of an asymmetric addition of indoles to nitroalkenes, employing a novel catalyst design [24]. The authors envisioned that a protonated 2-pyridyl substituent could increase the acidity of the

• biologically interesting β-amino acid derivatives (Table 2) [42]. In this work, the authors compared the results achieved by means of 4 with other urea- and thiourea-based organocatalysts in order to understand the effect of the acidity, the structural rigidity, and the bifunctionality of the promoter. These

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• been postulated that as the acidity of component HX is increased, the stronger the resulting hydrogen-bonding interaction Y···H–X is [15]. As a logical conclusion, it seems that multiple hydrogen-bonding interactions will provide a more defined conformation to the transition state, thus the catalysts

Base metal-catalyzed benzylic oxidation of (aryl)(heteroaryl)methanes with molecular oxygen

• Hans Sterckx,
• Johan De Houwer,
• Carl Mensch,
• Wouter Herrebout,
• Kourosch Abbaspour Tehrani and
• Bert U. W. Maes

Beilstein J. Org. Chem. 2016, 12, 144–153, doi:10.3762/bjoc.12.16

• the basicity of the pyridine nitrogen and not that much on the acidity of the methylene hydrogen. While the thermodynamical equilibrium constant between the imine and enamine tautomers predicts whether or not a substrate can be oxidized (see Supporting Information File 1), it does not provide an

A journey in bioinspired supramolecular chemistry: from molecular tweezers to small molecules that target myotonic dystrophy

• Steven C. Zimmerman

Beilstein J. Org. Chem. 2016, 12, 125–138, doi:10.3762/bjoc.12.14

• capability. However, Monte Carlo simulations by Blake and Jorgensen indicate that the cleft of 9 is actually a good host for chloroform and that the carboxylic acid is solvated by more than one chloroform molecule [21]. Another possibility is that the aromatic cleft might somehow decrease the acidity of the

Copper-catalyzed intermolecular oxyamination of olefins using carboxylic acids and O-benzoylhydroxylamines

• Brett N. Hemric and
• Qiu Wang

Beilstein J. Org. Chem. 2016, 12, 22–28, doi:10.3762/bjoc.12.4

• efficiencies were observed in the reactions with more acidic benzoic acids, indicating a correlation of their reactivity to their acidity which remains to be further clarified [44]. Furthermore, when trifluoroacetic acid was employed as an oxygen source, the free 1,2-amino alcohol 4g was isolated, possibly due

Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules

• Diego M. Andrada,
• Nicole Holzmann,
• Thomas Hamadi and
• Gernot Frenking

Beilstein J. Org. Chem. 2015, 11, 2727–2736, doi:10.3762/bjoc.11.294

• abilities [32][33]. However, experimental and computational evidences have revealed non-negligible π-acceptor properties [34][35][36][37][38]. In recent years, several strategies have successfully been developed for tuning the π-acidity of NHCs by changing substitution and structural patterns, such as the

• been developed to quantify the π-acceptor ability of carbenes [61][62]. Thus, NMR methods have been reported that allow the measurement of the π-acidity of NHCs [63]. Bertrand et al. and Ganter et al. have proposed the use of 31P and 77Se NMR chemical shift of the NHC-phenylphosphinidene and NHC

Copper-catalyzed arylation of alkyl halides with arylaluminum reagents

• Bijay Shrestha and
• Ramesh Giri

Beilstein J. Org. Chem. 2015, 11, 2400–2407, doi:10.3762/bjoc.11.261

• catalyzed by Pd and Ni, exploit a wide range of organometallic reagents of Mg, Zr, Zn, Sn, Al, B, Si and In as sources of nucleophiles. Among these metals/non-metals, Al offers a unique feature due to its high chemoselectivity and Lewis acidity [10][11][12]. In addition, Al also has low toxicity and is an