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Search for "photolysis" in Full Text gives 124 result(s) in Beilstein Journal of Organic Chemistry.

Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

  • Axel G. Griesbeck and
  • Melissa Reckenthäler

Beilstein J. Org. Chem. 2014, 10, 1143–1150, doi:10.3762/bjoc.10.114

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  • titanium species, photolysis at 254 and 300 nm, respectively, led only to trace amounts of the hydroxymethylation product 4 via a (triplet carbonyl) excited-state hydrogen-transfer process, obviously a sluggish process under these conditions (Table 1). In the presence of titanium complexes TiCln(OiPr)4−n
  • and the (more reactive and easier oxidizable) hydroxymethyl radicals. As shown in Table 5, this is actually the case for the semiconductor particle TiO2 P25 catalysis. If acetophenone is added to the photolysis solution constantly over a period of 24 h, the absolute amount of hydroxymethylation
  • the photolysis of TiO2 in the absence of additional acceptor compounds with formation of hydrogen and eventually formation of formaldehyde [46]. Both hydrogen and formaldehyde were also detected in our experiments by gas-phase analysis. Thus, higher amounts of hydroxymethyl radicals can be produced
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Published 19 May 2014

On the mechanism of photocatalytic reactions with eosin Y

  • Michal Majek,
  • Fabiana Filace and
  • Axel Jacobi von Wangelin

Beilstein J. Org. Chem. 2014, 10, 981–989, doi:10.3762/bjoc.10.97

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  • spectroscopic, synthetic, and apparative study has allowed a more detailed mechanistic rationalization of several recently reported eosin Y-catalyzed aromatic substitutions at arenediazonium salts. The operation of rapid acid–base equilibria, direct photolysis pathways, and radical chain reactions has been
  • addition of the photocatalyst eosin Y, 54% yield of the borylation product were obtained by direct photolysis (Scheme 4). These observations are in full accord with a report of direct reaction of thermally generated aryl cations (from arenediazonium salts) with bispinacolato diboron to give the
  • Deronzier from 1984 [32]. The significant overlap of the absorption spectra of the arenediazonium salt recorded before and after the addition of eosin Y (Figure 4) suggests that direct photolysis of the C–N bond could account for the erosion of product yield in the catalytic process due to competitive
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Published 30 Apr 2014

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

  • Christian Ley,
  • Julien Christmann,
  • Ahmad Ibrahim,
  • Luciano H. Di Stefano and
  • Xavier Allonas

Beilstein J. Org. Chem. 2014, 10, 936–947, doi:10.3762/bjoc.10.92

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  • of the complex kinetics underlying PCIS chemical reactions, allowing a better and simplest selection of chemicals combination. Results and Discussion In order to outline this behavior, the photochemical consumption of the dye (i.e., photolysis) was studied in a typical Type II and a 3-cpt PCIS based
  • reaction. Thus, according to Beer–Lambert's law, the absorbance of the system decreases during the reaction: this bleaching could be followed by UV–visible absorption spectroscopy. The photolysis of an acetonitrile solution of RB/TA was done within a 1 cm width cell with a monochromatic 532 nm laser diode
  • dye (see insert Figure 1). It should be noted that in the same conditions, no photolysis occurs for an acetonitrile solution of neat RB. To quantify the consumption of the PS, the photolysis quantum yield (Φphotolysis) was determined. Φphotolysis is defined by the ratio of the initial number of
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Published 25 Apr 2014

Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

  • Jacques Lalevée,
  • Sofia Telitel,
  • Pu Xiao,
  • Marc Lepeltier,
  • Frédéric Dumur,
  • Fabrice Morlet-Savary,
  • Didier Gigmes and
  • Jean-Pierre Fouassier

Beilstein J. Org. Chem. 2014, 10, 863–876, doi:10.3762/bjoc.10.83

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  • -trapping, laser flash photolysis, steady state photolysis, cyclic voltammetry and luminescence experiments. Keywords: LEDs; photoinitiators; photopolymerization; photoredox catalysis; Introduction Photoredox catalysis is now well-known and largely used in organic synthesis, especially in the development
  • panchromatic behavior in the 400–650 nm range. The PIC/Ph2I+/NVK system The photochemical properties of Ir(piq)2(tmd) A triplet-state lifetime of 1.1 μs has been determined for Ir(piq)2(tmd) by laser flash photolysis experiments. A relatively similar lifetime (1.3 μs) was previously measured for 3Ir(ppy)3 [68
  • + interaction is also in line with a fast photolysis of the PIC observed during the irradiation of Ir(piq)2(tmd)/Ph2I+ (Figure 8). In ESR spin-trapping experiments on irradiated Ir(piq)2(tmd)/Ph2I+ in the presence of phenyl-N-tert-butylnitrone (PBN), phenyl radicals are also detected (Figure 9). In the presence
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Published 15 Apr 2014

The chemistry of amine radical cations produced by visible light photoredox catalysis

  • Jie Hu,
  • Jiang Wang,
  • Theresa H. Nguyen and
  • Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

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  • lend support to some of the key steps in the catalytic cycle. An oxygen uptake experiment showed that 0.75 equiv of O2 was consumed for the complete conversion of N-phenyltetrahydroisoquinoline 13. This data strongly supports the role of O2 as the stoichiometric oxidant. Flash photolysis studies
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Published 01 Oct 2013

Damage of polyesters by the atmospheric free radical oxidant NO3: a product study involving model systems

  • Catrin Goeschen and
  • Uta Wille

Beilstein J. Org. Chem. 2013, 9, 1907–1916, doi:10.3762/bjoc.9.225

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  • are initially required in the polyester to promote further degradation on a large scale through chain and other processes. Reaction of polyester-model compounds 1–3 with NO3• from CAN photolysis Study of the products formed in the reaction of NO3• obtained from CAN photolysis provides the opportunity
  • these systems. Thus, CAN photolysis generates NO3• in the presence of excess NO3−, which acts as Brønsted base and mediates deprotonation of the initial radical cation 3•+ to give benzyl radical 7 [23], followed by transformation to the products 4–6. In the NO2•/O3 system, on the other hand, [NO3−] = [3
  • % acetonitrile within 2–3 hours. UV detection was performed at λ = 214 and 230 nm. Purity was assessed by analytical RP HPLC on an SGE Protecol C18 5 μM 250 × 4.6 mm column. Reactions with NO3• from CAN photolysis In a typical experiment 1.0 mmol of the model substrate and 4.0 mmol of CAN were dissolved in 5 and
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Published 20 Sep 2013

[3 + 2]-Cycloadditions of nitrile ylides after photoactivation of vinyl azides under flow conditions

  • Stephan Cludius-Brandt,
  • Lukas Kupracz and
  • Andreas Kirschning

Beilstein J. Org. Chem. 2013, 9, 1745–1750, doi:10.3762/bjoc.9.201

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  • of 2H-azirines 2 under inductive heating and photochemical conditions. The experiments were conducted at a concentration of 0.05 M. Optimization of the photolysis of vinyl azide 1a and trapping of nitrile ylide with acrylonitrile 4a under flow conditions. Supporting Information Supporting
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Published 26 Aug 2013

Thermochemistry and photochemistry of spiroketals derived from indan-2-one: Stepwise processes versus coarctate fragmentations

  • Götz Bucher,
  • Gernot Heitmann and
  • Rainer Herges

Beilstein J. Org. Chem. 2013, 9, 1668–1676, doi:10.3762/bjoc.9.191

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  • we investigate the fragmentation reactions of cyclic ketals. Three ketals with different ring sizes derived from indan-2-one were decomposed by photolysis and pyrolysis. Particularly clean is the photolysis of the indan-2-one ketal 1, which gives o-quinodimethane, carbon dioxide and ethylene. The
  • stepwise mechanisms may compete. Keywords: coarctate reaction; fragmentation; matrix isolation; photolysis; pyrolysis; spiroketal; Introduction Pericyclic reactions, according to the original definition, are characterized by a cyclic array of bond making and bond breaking [1][2][3]. At each atom
  • chosen as a reference system that cannot undergo a coarctate fragmentation. Results Photolysis and pyrolysis of the ketals. Photolysis (λexc = 254 nm, Hg low-pressure lamp) of indan-2-one ethylene ketal (1), matrix-isolated in Ar at 10 K, leads to the formation of CO2 (vs, ν = 2342.1 cm−1), o-xylylene
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Published 15 Aug 2013

Organotellurium-mediated living radical polymerization under photoirradiation by a low-intensity light-emitting diode

  • Yasuyuki Nakamura and
  • Shigeru Yamago

Beilstein J. Org. Chem. 2013, 9, 1607–1612, doi:10.3762/bjoc.9.183

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  • and 87500, with narrow MWDs (Mw/Mn = 1.18 and 1.33, respectively) were successfully synthesized by using a 10% transmittance ND filter (Table 2, runs 6 and 7). When the ditelluride is absent, polymerization is initiated by the direct photolysis of the carbon–tellurium bond of the organotellurium
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Published 07 Aug 2013

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

  • Martin Goez and
  • Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

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  • to radical pairs by laser flash photolysis. Without further action on the part of the experimenter, the radical pair mechanism then creates opposite polarizations in the geminate products, i.e., in the starting materials A and D regenerated by reverse electron transfer, and in the escaping free
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Published 19 Jul 2013

Homolytic substitution at phosphorus for C–P bond formation in organic synthesis

  • Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 1269–1277, doi:10.3762/bjoc.9.143

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  •  15) [42]. Photolysis of the esters in the presence of white phosphorus followed by oxidation with hydrogen peroxide yields alkylphosphonic acid. The efficient phosphination would stem from the highly strained structure and the weak P–P bonds of white phosphorus. After 13 years of silence, radical
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Published 28 Jun 2013

Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes

  • Roy T. McBurney and
  • John C. Walton

Beilstein J. Org. Chem. 2013, 9, 1083–1092, doi:10.3762/bjoc.9.120

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  • ]. Their weak N–O bonds selectively cleave on UV photolysis, particularly when sensitised with 4-methoxyacetophenone (MAP), thus facilitating investigations of the behaviour of both iminyl and alkoxycarbonyloxyl radicals R’OC(O)O•. A distinct advantage of these precursors is that they enable the iminyl
  • ) and the ketones ArC(R2)=O from imine hydrolyses. Photolysis of the more flexible precursor 4 gave a complex mixture of products. The MS and NMR data indicated that the main components were probably the corresponding imine ImH and ketone together with the iminyl radical dimer (Im2). Neither spiro- nor
  • stabilisation of spiro-cyclised radical 12a, these rate parameters seem to be very reasonable estimates (Table 3). Curiously, analysis of the products from a photolysis of 2a carried out at higher temperature (rt) in benzotrifluoride solvent, showed benzofuro[3,2-c]isoquinoline derivative 14a to be the main
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Published 04 Jun 2013

Design and synthesis of tag-free photoprobes for the identification of the molecular target for CCG-1423, a novel inhibitor of the Rho/MKL1/SRF signaling pathway

  • Jessica L. Bell,
  • Andrew J. Haak,
  • Susan M. Wade,
  • Yihan Sun,
  • Richard R. Neubig and
  • Scott D. Larsen

Beilstein J. Org. Chem. 2013, 9, 966–973, doi:10.3762/bjoc.9.111

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  • click chemistry. All were confirmed to maintain biological activity in a cell-based assay for inhibition of SRE-Luc expression. The functional activity of the most potent probe 24 was further confirmed in an assay for PC-3 cell migration. Photolysis of 24 in intact PC-3 cells followed by cell lysis
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Published 21 May 2013

Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

  • Jianhuai Ye,
  • Yoshihisa Fujiwara and
  • Manabu Abe

Beilstein J. Org. Chem. 2013, 9, 925–933, doi:10.3762/bjoc.9.106

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  • entropy effect were found to play crucial roles in increasing the lifetime. Keywords: laser flash photolysis; lifetime; singlet diradicals (biradicals); substituent effect; π-single bond; Introduction Localized singlet diradicals are key intermediates in processes involving the homolytic bond-cleavage
  • photolysis technique was used for the generation of DRc–g from the corresponding azoalkanes AZc–g (Scheme 2). Results and Discussion Synthesis of AZc–g and their steady-state photolyses. The precursor azoalkanes AZc–g were prepared in an analogous method to the synthesis of AZa,b [28] (Scheme 3). Pyrazoles
  • . Detection of singlet diradicals DRc–g. The detection of singlet diradicals DRc–g was examined by the photochemical denitrogenation of azoalkanes AZc–g in a glassy matrix of 2-methyltetrahydrofurane (MTHF) at 80 K, [AZ] ≈ 4 × 10−3 mol/L, and by the laser flash photolysis experiments of AZc–g at room
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Published 14 May 2013

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

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  • photocatalysts. Successful results in terms of rates of polymerization and final conversions were obtained. The strong MO coupling between the six different cores and the pyrene moiety was studied by DFT calculations. The different chemical intermediates are characterized by ESR and laser flash photolysis
  • halide for FRP. The monomers investigated are given in Scheme 4. The mechanisms are analyzed by electron spin resonance (ESR), steady-state photolysis, fluorescence and laser flash photolysis (LFP). The ability of Co_Pys to behave as new organophotocatalysts is also discussed. Results and Discussion
  • to radical polymerization. Laser flash photolysis Upon laser excitation of Py_3 at 355 nm, a triplet state T1 characterized by a maximum absorption at ~420 nm and a rather long lifetime is formed (t > 4 μs) (Figure S2 in Supporting Information File 1). This T1 state is similar to that of Py_1 [31
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Published 07 May 2013

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

  • Maurizio Fagnoni,
  • Stefano Protti,
  • Davide Ravelli and
  • Angelo Albini

Beilstein J. Org. Chem. 2013, 9, 800–808, doi:10.3762/bjoc.9.91

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  • the presence of a variety of donors (D–X, step a). In all of the above cases, the generated radical anion (A–Y•−) is a persistent species easily detected by laser flash photolysis. This approach applies to a variety of donors, including amines [12][13], carboxylic acids or their derivatives [14][15
  • photolysis experiments had shown that DABCO formed the TCB radical anion on the nanosecond time scale just as the other tertiary amines [53]. However, no reaction able to eliminate radical cations was viable in this case, and thus BET predominated (path a' in Scheme 2 and path α in Figure 4). Irreversible
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Published 24 Apr 2013

4-Pyridylnitrene and 2-pyrazinylcarbene

  • Curt Wentrup,
  • Ales Reisinger and
  • David Kvaskoff

Beilstein J. Org. Chem. 2013, 9, 754–760, doi:10.3762/bjoc.9.85

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  • Curt Wentrup Ales Reisinger David Kvaskoff School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia 10.3762/bjoc.9.85 Abstract Both flash vacuum thermolysis (FVT) and matrix photolysis generate 2-diazomethylpyrazine (22) from 1,2,3-triazolo[1,5-a
  • -diazacyclohepta-1,2,4,6-tetraene (20). Further photolysis causes ring opening to the ketenimine 27. Keywords: carbene–nitrene interconversion; diazepines; flash vacuum thermolysis; matrix photochemistry; nitrile ylides; reactive intermediates; Introduction The carbene–nitrene interconversion exemplified with
  • and Discussion Here, we report details of the FVT as well as matrix photolysis reactions of 4-azidopyridine (18) and the isomeric triazolo[1,5-a]pyrazine (24) and its precursor, 2-(5-tetrazolyl)pyrazine (23). Furthermore, we report evidence for ring expansion as well as ring opening of 4
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Published 17 Apr 2013
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  • ) under conditions of photolysis in solution or in matrices as well as under flash vacuum thermolysis (FVT) (Scheme 2) [1][7][8][9][10]. The end products under FVT conditions are the 2- and 3-cyanopyrroles 7 and 8 [10][11]. A competing ring-opening of 2-pyridylnitrenes to cyanobutadienylnitrenes can lead
  • rearrange to 3-pyridylnitrenes, whereas 4-pyrimidinylcarbenes do not necessarily rearrange to 3-pyridylnitrenes (see 55 below). 2-Phenyl-3-quinolylnitrene Matrix photolysis of 3-azido-2-phenylquinoline (44) at λ = 308 nm or 310–390 nm affords a blue nitrile ylide 47 (observed IR 2220, 2154 cm−1; calcd
  • (B3LYL/6-31G*) 2233, 2171 cm−1; UV–vis λmax 400 and 680 nm) (Scheme 11, Figure 2 and Figure 3). It could be converted to the seven-membered ring ketenimine 46 (IR: 1920; calcd: 1921 cm−1) on photolysis above 550 nm. The ketenimine 46 was again converted to ylide 47 on photolysis at 310–390 nm. We assume
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Published 17 Apr 2013

High-spin intermediates of the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine

  • Sergei V. Chapyshev,
  • Denis V. Korchagin,
  • Patrik Neuhaus and
  • Wolfram Sander

Beilstein J. Org. Chem. 2013, 9, 733–742, doi:10.3762/bjoc.9.83

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  • Abstract In contrast to theoretical expectations, the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine in argon at 5 K gives rise to EPR peaks of just two triplet mononitrenes, two quintet dinitrenes, and a septet trinitrene. EPR spectral simulations in combination with DFT calculations show that
  • spectroscopy; high-spin states; matrix isolation; nitrenes; photolysis; reactive intermediates; Introduction High-spin nitrenes are highly reactive intermediates formed during photolysis or thermolysis of aromatic polyazides. Both these processes are widely used in modern science and technology [1][2][3][4][5
  • ][6]. When aromatic polyazides contain nonequivalent azido groups, these groups can undergo selective photolysis, providing important information about the selective cleavage of chemical bonds in organic molecules with light. The direction and selectivity of such processes can be monitored with EPR
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Published 16 Apr 2013

New reactive intermediates in organic chemistry

  • Götz Bucher

Beilstein J. Org. Chem. 2013, 9, 613–614, doi:10.3762/bjoc.9.67

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  • and hence can be studied for an extended period of time; or laser flash photolysis, where the reactive intermediate is generated by a very short pulse of laser light, and can be investigated in real time; or specialised mass-spectrometric techniques such as ion cyclotron resonance MS. Due to the
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Editorial
Published 26 Mar 2013

A chemist and biologist talk to each other about caged neurotransmitters

  • Graham C.R. Ellis-Davies

Beilstein J. Org. Chem. 2013, 9, 64–73, doi:10.3762/bjoc.9.8

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  • most purposes. I have been confused by some reports of “rates of reactions” being given as a time course for steady-state photolysis over many seconds or minutes [45], whereas other reports show rates from laser flash photolysis [3][61]. Can you help clarify this? Chemist: Only the latter should be
  • called a rate. The former is simply a way of measuring the quantum yield by determining the half-time (hence “rate”) of photolysis under some set of defined irradiation conditions. However, even with the former measurement care must be taken. The chemical reactions of release can be quite complex, so the
  • than MNI-Glu [27] (ε = 4,300/M/cm). The second property is the quantum yield of photolysis (chemists use the symbol Φ for this). This measures how many excited molecules give a product, with the normal maximum being 1. Photochemical efficiency is ε·Φ. So, to some extent, a large ε can make up for a
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Published 11 Jan 2013

Flow photochemistry: Old light through new windows

  • Jonathan P. Knowles,
  • Luke D. Elliott and
  • Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

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  • up the photolysis of a strongly absorbing chromophore. Here, a thin film of the substrate solution flows down a glass plate or tube in close proximity to the light source. The short path length leads to very efficient irradiation. The downside is that residence time is short and often the solution
  • synthetic use of titanium dioxide as a photocatalyst is in the alkylation of amines. As shown in Scheme 10, photolysis of a mixture of benzylamine (28) and ethanol in the presence of a titanium dioxide photocatalyst gave the ethylamine 29 in high conversion, employing both the oxidative (ethanol to
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Published 21 Nov 2012

The chemistry of bisallenes

  • Henning Hopf and
  • Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

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Published 15 Nov 2012

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

  • Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

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  • catalytic cycle was ultimately achieved following the discovery that the reaction of (PNP)Ir═C(H)Ot-Bu with organic azides leads to the formation of tert-butyl formimidates and (PNP)Ir–N2, which is a suitable precursor for C–H activation of MTBE upon photolysis [78] (Scheme 15). Although the presence of
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Published 18 Sep 2012

A quantitative approach to nucleophilic organocatalysis

  • Herbert Mayr,
  • Sami Lakhdar,
  • Biplab Maji and
  • Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

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  • corresponding N parameters – LFP = laser flash photolysis. Comparison of the electrophilicities of cinnamaldehyde-derived iminium ions 3a–3i. Nucleophiles used in iminium activated reactions [35][42][44][45][46][47][48][49][50][51][52]. Counterion effects in electrophilic reactions of iminium ions 3a-X (at 20
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Published 05 Sep 2012
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