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

Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors

• Morgan Hans,
• Jan Lorkowski,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2015, 11, 2318–2325, doi:10.3762/bjoc.11.252

• diazabutadiene cleanly precipitated from the reaction mixture and could be isolated in high yield by simple filtration and washing. For the critical cyclization step of IDip*·HCl, Markó et al. ingeniously took advantage of the Lewis acidity of zinc chloride to activate paraformaldehyde and of its coordinating

Photoinduced 1,2,3,4-tetrahydropyridine ring conversions

• Baiba Turovska,
• Henning Lund,
• Viesturs Lūsis,
• Anna Lielpētere,
• Edvards Liepiņš,
• Sergejs Beljakovs,
• Inguna Goba and
• Jānis Stradiņš

Beilstein J. Org. Chem. 2015, 11, 2166–2170, doi:10.3762/bjoc.11.234

• deprotonated efficiently in the presence of superoxide including Hantzsch 1,4-dihydropyridines [31][32]. Cation radicals have increased acidity comparing to the parent molecules from which they are derived by oxidation [33][34][35]. Consequently, their deprotonation proceeds more efficiently. Photooxygenation

Stereoselective synthesis of hernandulcin, peroxylippidulcine A, lippidulcines A, B and C and taste evaluation

• Marco G. Rigamonti and
• Francesco G. Gatti

Beilstein J. Org. Chem. 2015, 11, 2117–2124, doi:10.3762/bjoc.11.228

• Pd(TFA)2 catalyzed dehydrogenation on the silyl enol ether 10 and in the presence of Na2HPO4 buffer, in order to mitigate the detrimental acidity of TFA. However, 11 was produced in a modest yield of 21%, because, even at these mild conditions, 10 reconverted to the initial ketone 9 faster than its

Efficient synthesis of π-conjugated molecules incorporating fluorinated phenylene units through palladium-catalyzed iterative C(sp²)–H bond arylations

• Fatiha Abdelmalek,
• Fazia Derridj,
• Safia Djebbar,
• Jean-François Soulé and
• Henri Doucet

Beilstein J. Org. Chem. 2015, 11, 2012–2020, doi:10.3762/bjoc.11.218

• )benzofuran (20) only reacted through the activation of the electron-deficient phenyl ring to afford the heteroaryl triad 28 in 56% yield. We imputed this shift of regioselectivity to the high acidity of the C–H bond flanked by the two fluorine atoms. Then, the regioselectivity of Pd-catalyzed second direct

Lewis acid-promoted hydrofluorination of alkynyl sulfides to generate α-fluorovinyl thioethers

• Davide Bello and
• David O'Hagan

Beilstein J. Org. Chem. 2015, 11, 1902–1909, doi:10.3762/bjoc.11.205

• 3HF·Et3N. In light of these observations, our working hypothesis is that the Lewis acid acts to increase the acidity of the 3HF·Et3N by sequestering fluoride ions as relatively unreactive metal fluorides; thus, the alkynyl sulfides are activated by protonation possibly through an intermediate such as A as

Deproto-metallation of N-arylated pyrroles and indoles using a mixed lithium–zinc base and regioselectivity-computed CH acidity relationship

• Mohamed Yacine Ameur Messaoud,
• Ghenia Bentabed-Ababsa,
• Madani Hedidi,
• Aïcha Derdour,
• Floris Chevallier,
• Yury S. Halauko,
• Oleg A. Ivashkevich,
• Vadim E. Matulis,
• Laurent Picot,
• Valérie Thiéry,
• Thierry Roisnel,
• Vincent Dorcet and
• Florence Mongin

Beilstein J. Org. Chem. 2015, 11, 1475–1485, doi:10.3762/bjoc.11.160

• using the DFT B3LYP method in order to rationalize the experimental results. Keywords: CH acidity; indoles; iodolysis; mixed lithium–zinc bases; pyrroles; Introduction Pyrrole occurs in very important natural products such as tetrapyrrolic (linear) bilirubinoids, and (cyclic) porphyrins and corrins

• , Figure 4, see Supporting Information File 2). Computational aspects There is a lack of data on the acidity of N-substituted pyrroles and indoles in the literature. NH acidity of unsubstituted pyrrole and indole in DMSO was measured by Bordwell [48] and computed by means of semi-empirical AM1 [49] and ab

• recently [42][52]. The results of quantum chemical calculations on CH acidity of the different N-arylated pyrroles 1 and indoles 2, obtained both for THF solution (Figure 5) and gas phase (see Supporting Information File 1), are presented in the current paper. A potential acidity of the methoxy groups in

Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• of the ligand L. This corresponds to a decrease in the Lewis acidity of the cobalt center. Consequently, the picture evolves to the reaction of an electrophilic CO2 molecule with a nucleophilic alkoxide chain connected to a cobalt(III) center. The CO2 molecule reacts via the carbon atom with the

Synthesis of icariin from kaempferol through regioselective methylation and para-Claisen–Cope rearrangement

• Qinggang Mei,
• Chun Wang,
• Zhigang Zhao,
• Weicheng Yuan and
• Guolin Zhang

Beilstein J. Org. Chem. 2015, 11, 1220–1225, doi:10.3762/bjoc.11.135

• unsatisfactory, even when prolonging the reaction time to 36 h or raising the temperature to 100 °C. By carefully investigating the two routes in Scheme 3, we assumed that an appropriate base is in favor of the [1,5]H σ migration in route 2, as well as lowering the acidity of Eu(fod)3 to prevent 12b from

Cathodic hydrodimerization of nitroolefins

• Michael Weßling and
• Hans J. Schäfer

Beilstein J. Org. Chem. 2015, 11, 1163–1174, doi:10.3762/bjoc.11.131

• −0.95 V vs SCE. The results indicate: an increased acidity favours the formation of oxime 5 (Table 1, Nr. 1), whilst without a proton donor the olefin presumably is polymerized to a large extent (Table 1, Nr. 2). The addition of acetic acid in portions appears to be a good choice as a too high proton

Thiazole formation through a modified Gewald reaction

• Carl J. Mallia,
• Lukas Englert,
• Gary C. Walter and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2015, 11, 875–883, doi:10.3762/bjoc.11.98

• (Figure 2) thus helping to identify certain attributes of the mechanism. For example, 2-phenylacetonitrile (44) failed to react most likely due to the lower acidity of the α-methylene protons. Diethyl 2-cyanomalonate (45), also proved unreactive, this substrate would be expected to form an extensively

Photocatalytic nucleophilic addition of alcohols to styrenes in Markovnikov and anti-Markovnikov orientation

• Martin Weiser,
• Sergej Hermann,
• Alexander Penner and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2015, 11, 568–575, doi:10.3762/bjoc.11.62

• significantly slower, since longer irradiations were needed. Only the addition of phenol failed completely. Since isopropanol and tert-butanol as sterically demanding nucleophiles gave the corresponding addition products in good yields, it was assumed that the acidity of benzyl alcohol, and more significantly

Fluoride-driven ‘turn on’ ESPT in the binding with a novel benzimidazole-based sensor

• Kai Liu,
• Xiaojun Zhao,
• Qingxiang Liu,
• Jianzhong Huo,
• Bolin Zhu and
• Shihua Diao

Beilstein J. Org. Chem. 2015, 11, 563–567, doi:10.3762/bjoc.11.61

• atom is transferred to an electronegative atom at the excited state [2][17][18]. By regulating the proton acidity of the H-bond donor which plays a vital role in the ESPT process, the biologically and chemically important anion would be distinguished by the different optical outputs for the interaction

• indicated the occurrence of hydrogen-bonding interaction between BIP and F−. Moreover, the acidity of the OH group of BIP was expected to be enhanced by anion binding, and the ESPT channel would be open [8][9][10][15]. The subsequent spectral behavior proved our assumption. The new peak at 376 nm occurred

• was 8.79 × 105 M−1, which was bigger than that obtained from UV–vis spectroscopy. This suggested the enhancement of the phenolic OH acidity by the photoexcitation [2][11][12][13][14][15]. Moreover, fluoride-dependent fluorescent intensity at 376 nm displayed an excellent linearity (R = 0.9880) in the