New core-pyrene π structure organophotocatalysts usable as highly efficient photoinitiators

• Sofia Telitel,
• Frédéric Dumur,
• Thomas Faury,
• Bernadette Graff,
• Mohamad-Ali Tehfe,
• Didier Gigmes,
• Jean-Pierre Fouassier and
• Jacques Lalevée

Beilstein J. Org. Chem. 2013, 9, 877–890, doi:10.3762/bjoc.9.101

• ]; the calculated ΔG is −1.16 eV). They correspond to an efficient electron transfer followed by the usual fast generation of radicals from the radical anion species (r5–r7 in Scheme 5) or an electron/proton transfer with the amine (r8 in Scheme 5). ESR spin trapping experiments In ESR spin trapping

Utilizing the σ-complex stability for quantifying reactivity in nucleophilic substitution of aromatic fluorides

• Magnus Liljenberg,
• Tore Brinck,
• Tobias Rein and
• Mats Svensson

Beilstein J. Org. Chem. 2013, 9, 791–799, doi:10.3762/bjoc.9.90

• hydrogen bonds from the NH2-group, and that the proton transfer to form HF takes place late in the concerted reaction step going from the σ-complex via TS2 to the products. An analysis of the energy differences between the three stationary points shows that the potential energy surface is extremely flat in

Enantioselective reduction of ketoimines promoted by easily available (S)-proline derivatives

• Martina Bonsignore,
• Maurizio Benaglia,
• Laura Raimondi,
• Manuel Orlandi and
• Giuseppe Celentano

Beilstein J. Org. Chem. 2013, 9, 633–640, doi:10.3762/bjoc.9.71

• the HF/3-21G level [31]. Inspection of the imaginary frequency of the two TSs, as well as IRC results, clearly indicates that the reaction, while not synchronous, is indeed concerted, since proton and hydride transfer are both occurring: while the proton transfer from the carboxylic group to the imine

A computational study of base-catalyzed reactions of cyclic 1,2-diones: cyclobutane-1,2-dione

• Nargis Sultana and
• Walter M. F. Fabian

Beilstein J. Org. Chem. 2013, 9, 594–601, doi:10.3762/bjoc.9.64

• nucleophile involved in the formation of Int1 actually is a water molecule, since formation of the C1–O3 bond is accompanied by proton transfer H3 to O4 of the original hydroxide anion (Figure 2). An analogous concerted addition–proton transfer has also been calculated previously for the benzilic acid type

• of an extended conformation Int2’ was attempted. However, such a structure collapsed upon geometry optimization in a concerted proton transfer–nucleophilic addition reaction to intermediate Int2a. By a simple acid–base equilibrium (alcoholate–carboxylic acid → alcohol–carboxylate), this intermediate

• bicyclic intermediate Int4 was found (Figure 4). Furthermore, this intermediate did not react to product P3 but instead through a concerted ring opening and proton transfer to P3a. The anticipated product P3 of path C is a γ-oxocarboxylate. Such γ-oxocarboxylic acids or carboxylates are prone to ring–chain

Complete σ* intramolecular aromatic hydroxylation mechanism through O₂ activation by a Schiff base macrocyclic dicopper(I) complex

• Albert Poater and
• Miquel Solà

Beilstein J. Org. Chem. 2013, 9, 585–593, doi:10.3762/bjoc.9.63

• and C–O bond formation, followed finally by a proton transfer to an alpha aromatic carbon that immediately yields the product [CuII2(bsH2m-O)(μ-OH)]2+. Keywords: aromatic hydroxylation; C–H bond activation; C–H functionalization; copper; DFT calculations; mechanism; Schiff base; Introduction Bearing

• aromatic proton transfer to the nearer oxygen atom with an upper barrier of only 1.4 kcal·mol−1 [40]. However, for bsH2m the distance between the two aromatic rings is always too large for them to help each other. Indeed bsH2m is significantly more rigid, and this factor reduces the degrees of free

Intramolecular carbolithiation cascades as a route to a highly strained carbocyclic framework: competition between 5-exo-trig ring closure and proton transfer

• William F. Bailey and
• Justin D. Fair

Beilstein J. Org. Chem. 2013, 9, 537–543, doi:10.3762/bjoc.9.59

• after two cyclizations by a proton transfer that occurs by an intermolecular process catalyzed by trace amounts of endo-5-methyl-2-methylenebicyclo[2.2.1]heptane present in reaction mixtures as a consequence of inadvertent quenching of an intermediate alkyllithium during prolonged reaction times at room

• temperature. Keywords: carbolithiation cascade; carbometallation; intramolecular carbolithiation; intermolecular proton transfer; lithium–halogen exchange; strained hydrocarbons; Introduction The first publication describing an intramolecular carbolithiation appeared in 1968: Drozd and co-workers reported

• -hexenyllithium rearrange rapidly by [1,4]-proton transfer to afford the allylic species [17]. In fact, the absence of proton transfers that would compromise 5-exo cyclization of 5-hexenyllithiums is a hallmark of this chemistry. Intrigued by these observations, we were prompted to investigate the possibility of

Electron and hydrogen self-exchange of free radicals of sterically hindered tertiary aliphatic amines investigated by photo-CIDNP

• Martin Goez,
• Isabell Frisch and
• Ingo Sartorius

Beilstein J. Org. Chem. 2013, 9, 437–446, doi:10.3762/bjoc.9.46

• rapidly produced by in-cage proton transfer, and the CIDNP kinetics are due to hydrogen self-exchange between escaping D• and DH. For TIPA, the activation parameters of both self-exchange reactions were determined. Outer-sphere reorganization energies obtained with the Marcus theory gave very good

• varying involvement of polar intermediates. Often, they are true two-step processes with an initial full charge transfer to give a radical ion pair, which then undergoes a proton transfer [1][2][3][4][5][6][7]; partial charge transfer (i.e., formation of an exciplex) as the first step has also been

• system, namely, hydrogen self-exchange and almost energetically neutral proton transfer. Figure 3 displays the outcome of a time-dependent CIDNP experiment on TIPA sensitized by XA. This amine exhibits the peculiarity that its CIDNP spectra are completely dominated by the emissive doublet of the β

Caryolene-forming carbocation rearrangements

• Quynh Nhu N. Nguyen and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2013, 9, 323–331, doi:10.3762/bjoc.9.37

• -10-ol, reveal two mechanisms for caryolene formation: one involves a base-catalyzed deprotonation/reprotonation sequence and tertiary carbocation minimum, whereas the other (with a higher energy barrier) involves intramolecular proton transfer and the generation of a secondary carbocation minimum and

• -membered rings [1][8][18][19][20][21][22]. The C2=C3 π-bond was then expected to attack C10 to form the 4-membered ring (see C), in analogy to previously proposed mechanisms for caryophyllene formation [21][23]. An intramolecular proton transfer from the C15 methyl group to the nearby C6=C7 π-bond could

• side of the ring as the first-formed cyclobutane, converged to the structure of C shown in Figure 3 [41]. Locating a pathway for the conversion of C to D (Scheme 1) also proved difficult. We expected proton transfer from the C15 methyl group to C6 of the C6=C7 π-bond to result in tertiary carbocation D

Presence or absence of a novel charge-transfer complex in the base-catalyzed hydrolysis of N-ethylbenzamide or ethyl benzoate

• Shinichi Yamabe,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2013, 9, 185–196, doi:10.3762/bjoc.9.22

• complex. Then, the hydrolysis occurs as a nonequilibrium route according to Le Chatelier's principle (Scheme 5). The scheme will be evaluated by comparing the calculated energies. As the alternative route to Int1(es), TS2(es) was obtained. At TS2(es), C∙∙∙O cleavage and the proton transfer occur

• simultaneously. This process is different to that thought so far (C∙∙∙O scission only forming C2H5O−). Formation of the unstable ethoxide ion is avoided by the concomitant proton transfer. After TS2(es), the {Ph–COOH + Et–OH + OH−(H2O)15} intermediate (Int2(es)) is afforded. The combination of Ph–COOH and OH

• − leads to TS3(es), where the double proton transfer is involved. After TS3(es), the product of {Ph–COO− + Et–OH + (H2O)16} is generated. Figure 4 demonstrates that the hydrolysis of ethyl benzoate has three elementary processes (except TS2'(es)). The ethoxide-ion intermediate and the zwitterion shown in

Palladium-catalyzed C–N and C–O bond formation of N-substituted 4-bromo-7-azaindoles with amides, amines, amino acid esters and phenols

• Rajendra Surasani,
• Dipak Kalita,
• A. V. Dhanunjaya Rao and
• K. B. Chandrasekhar

Beilstein J. Org. Chem. 2012, 8, 2004–2018, doi:10.3762/bjoc.8.227

• -deficient pyridine ring. The pKa value of 7-azaindole is ~4.9, and it undergoes self-association through hydrogen-bonding to form a dimer in solution and phototautomerizes by an excited-state double-proton-transfer (ESDPT) process [1][48]. In the presence of copper or palladium catalysts azaindole undergoes

Palladium-catalyzed dual C–H or N–H functionalization of unfunctionalized indole derivatives with alkenes and arenes

• Gianluigi Broggini,
• Egle M. Beccalli,
• Andrea Fasana and
• Silvia Gazzola

Beilstein J. Org. Chem. 2012, 8, 1730–1746, doi:10.3762/bjoc.8.198

• the reactivity of some Ar-Pd(II) complexes with arenes (through a proton-transfer palladation mechanism), depending on the C–H acidity rather than the arene nucleophilicity. Synthetic procedures based on this strategy allowed the direct arylation at C-2 and C-3 positions of indoles 9 with a high

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters

• Takuya Uno,
• Yusuke Kobayashi and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2012, 8, 1499–1504, doi:10.3762/bjoc.8.169

• -imino ester 4. Intermolecular proton transfer from III gives intermediate IV, which could release the product 5 and the carbene I to complete the catalytic system. We speculated that the desired product 5 is thermodynamically more stable than 6 and the formation of 5 is the irreversible step, from the

Synthesis of new pyrrole–pyridine-based ligands using an in situ Suzuki coupling method

• Matthias Böttger,
• Björn Wiegmann,
• Steffen Schaumburg,
• Peter G. Jones,
• Wolfgang Kowalsky and
• Hans-Hermann Johannes

Beilstein J. Org. Chem. 2012, 8, 1037–1047, doi:10.3762/bjoc.8.116

• of chemistry. The pyrrole–pyridine structural motif is featured in current studies, owing to its complexation properties towards first-row transition metals (Fe, Co, Ni, Cu, Zn) [18] and ruthenium [19]. The intramolecular proton transfer of these species is also of interest for vibrational

Volatile organic compounds produced by the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria 85-10

• Teresa Weise,
• Marco Kai,
• Anja Gummesson,
• Armin Troeger,
• Stephan von Reuß,
• Silvia Piepenborn,
• Francine Kosterka,
• Martin Sklorz,
• Ralf Zimmermann,
• Wittko Francke and
• Birgit Piechulla

Beilstein J. Org. Chem. 2012, 8, 579–596, doi:10.3762/bjoc.8.65

• information we carried out GC/MS and proton transfer reaction (PTR)–MS analyses with X. c. pv. vesicatoria 85-10. In addition, we aimed at structure elucidation and on temporal variation of profiles of volatiles produced upon growth on different media. Results and Discussion Effect of Xanthomonas campestris

• , proton transfer reaction mass spectrometry (PTR–MS) was additionally used. The analyses of volatiles emitted by X. c. pv. vesicatoria 85-10 were performed after three days of incubation on NB and NBG in Petri dishes (Figure 4A and Figure 4B, respectively). At least 27 m/z values were found in the mass

• range between 30 and 250 with signals that were significantly enhanced (5% confidence level) compared to those of the blank control samples. If the proton affinity of an analyte molecule is higher than the one of H3O+ the proton transfer reaction is more or less quantitative (quasi-first-order reaction

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system

• Caterina Fraschetti,
• Matthias C. Letzel,
• Antonello Filippi,
• Maurizio Speranza and
• Jochen Mattay

Beilstein J. Org. Chem. 2012, 8, 539–550, doi:10.3762/bjoc.8.62

• the effective probability that the necessary proton transfer from T to B occurs. Rigid resorcin[4]arenes as chiral selectors of amino acids and neurotransmitters. Further insights into the molecular recognition of basket resorcin[4]arene V towards representative chiral molecules were gathered. For

Synthesis and photooxidation of styrene copolymer bearing camphorquinone pendant groups

• Branislav Husár,
• Norbert Moszner and
• Ivan Lukáč

Beilstein J. Org. Chem. 2012, 8, 337–343, doi:10.3762/bjoc.8.37

• (CQ) in the presence of H-atom donors such as ethers (H abstraction), or more efficiently tertiary amines (electron/proton transfer), is known to be an effective photoinitiator for curing methacrylate-based dental restorative resins [1][2][3][4][5][6][7][8][9]. CQ photochemistry in solution in the

Efficient, highly diastereoselective MS 4 Å-promoted one-pot, three-component synthesis of 2,6-disubstituted-4-tosyloxytetrahydropyrans via Prins cyclization

• Naseem Ahmed and
• Naveen Kumar Konduru

Beilstein J. Org. Chem. 2012, 8, 177–185, doi:10.3762/bjoc.8.19

• same distereoselectivity and product yields (83–89%, Table 2, entries 16–18). From a mechanistical point of view, these reactions are similar to the Prins cyclization [41]. First, the aldehyde got activated by PTSA protonation followed by a nucleophilic attack of the homoallylic alcohol and proton

• transfer to the hydroxy group. Then, a nucleophilic attack of PTSA resulted in α-tosyloxyether formation after losing a water molecule. In the α-tosyloxyether, the delocalization of lone-pair electrons on the oxygen atom led to the removal of the tosylate group and oxo-carbenium ion intermediate formation

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

• Jiří Kulhánek and
• Filip Bureš

Beilstein J. Org. Chem. 2012, 8, 25–49, doi:10.3762/bjoc.8.4

• hyperpolarizabilities βzzz at 27500 and 13600 au, the closed form showed only diminished nonlinearities due to the interruption of efficient D-A conjugation. Compounds showing excited-state intramolecular proton transfer (ESIPT) represent another example of switchable NLO-phores (Scheme 4). Donor- and acceptor

• -substituted push–pull systems 66 based on 2-(2-hydroxyphenyl)benzo[d]imidazole showed efficient photoinduced blue-green proton-transfer fluorescence [73][74]. Taking the amino/nitro-substituted derivative as an example (R1 = NO2; R2 = H; R3 = NH2; LEN [73]), this compound showed absorption and emission maxima

Asymmetric synthesis of quaternary aryl amino acid derivatives via a three-component aryne coupling reaction

• Elizabeth P. Jones,
• Peter Jones,
• Andrew J. P. White and
• Anthony G. M. Barrett

Beilstein J. Org. Chem. 2011, 7, 1570–1576, doi:10.3762/bjoc.7.185

• 1 the ensuing carbanion 5 was not aryl as expected but instead benzylic, due to an inter- or intramolecular proton transfer. Kinetic protonation of this anion on the face opposite to the isopropyl group accounted for the observed diastereoselectivity of the reaction (Scheme 3). To extend this

Directed aromatic functionalization in natural-product synthesis: Fredericamycin A, nothapodytine B, and topopyrones B and D

• Charles Dylan Turner and
• Marco A. Ciufolini

Beilstein J. Org. Chem. 2011, 7, 1475–1485, doi:10.3762/bjoc.7.171

• considerably more efficiently than 69 (over 60% isolated yield), and that it was accompanied by only small amounts of the debrominated byproduct 73. We thus concluded that the low yield of 68 must have been the consequence of the consumption of a portion of aryllithium species 67 through parasitic proton

• -transfer steps, probably involving one of its benzylic positions as the proton donor. While the yield of 69 could not be improved, its preparation in the fashion just described is highly convergent. Furthermore, an overall yield around 20% for a one-pot sequence that involves three major steps (addition of

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

• Benito Alcaide and
• Pedro Almendros

Beilstein J. Org. Chem. 2011, 7, 622–630, doi:10.3762/bjoc.7.73

• . Deauration and proton transfer leads to adduct 27 with concomitant regeneration of the Au(III) species (Scheme 15). Regiocontrolled gold/Brønsted acid co-catalyzed direct bis-heterocyclization of alkynyl-β-lactams allows the efficient synthesis of optically pure tricyclic bridged acetals bearing a 2

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

• Ryuji Hayashi,
• John B. Feltenberger,
• Andrew G. Lohse,
• Mary C. Walton and
• Richard P. Hsung

Beilstein J. Org. Chem. 2011, 7, 410–420, doi:10.3762/bjoc.7.53

• 1,3-hydrogen shift than the neutral one. Lastly, a non-radical proton-transfer like mechanism could also be at play under conditions using protic solvents or owing to the presence of trace of amount of water (Figure 2, right). These last two models also reveal some insight into the E-selectivity given

pH-Responsive chromogenic-sensing molecule based on bis(indolyl)methene for the highly selective recognition of aspartate and glutamate

• Litao Wang,
• Xiaoming He,
• Yong Guo,
• Jian Xu and
• Shijun Shao

Beilstein J. Org. Chem. 2011, 7, 218–221, doi:10.3762/bjoc.7.29

• Academy of Sciences, Beijing 100039, P. R. China 10.3762/bjoc.7.29 Abstract Bis(indolyl)methene displays high selectivity and sensitivity for aspartate and glutamate in water-containing medium based on the proton transfer signaling mode. The presence of acid can easily induce proton transfer to the basic

• )methene; colorimetric sensor; molecular recognition; proton transfer; Introduction The development of artificial receptors for the selective recognition of biologically important species has attracted much attention [1][2]. However, compared to the large number of chromo/fluororeceptors for cations or

• absorption spectra may be ascribed to proton transfer to 1. Because of the acidic characteristic of Asp (pI = 2.77) and Glu (pI = 3.22) [20], they are quite capable of protonating 1, which modulates the internal charge transfer (ICT) and results in a drastic spectral change from 435 nm to 500 nm arising from

Catalysis: transition-state molecular recognition?

• Ian H. Williams

Beilstein J. Org. Chem. 2010, 6, 1026–1034, doi:10.3762/bjoc.6.117

• coordinates for nucleophilic substitution and proton transfer from Glu172, showed no requirement for protonation of the activated nucleofuge [24]. PMFs, with respect to the nucleophilic substitution reaction coordinate for both the wild-type and the Tyr69Phe mutant, computed with the same QM/MM MD method

EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

• Giorgio Bencivenni,
• Riccardo Cesari,
• Daniele Nanni,
• Hassane El Mkami and
• John C. Walton

Beilstein J. Org. Chem. 2010, 6, 713–725, doi:10.3762/bjoc.6.84

• . Ipso attack by radical 13a on the aniline would lead to the production of delocalised radical 15. Elimination of MeOMCl3− would then yield radical 16, which, on protonation, would afford the observed long-lived dimer radical cations 17+•. Of course, proton transfer could occur earlier in the reaction