Radical polymerization by a supramolecular catalyst: cyclodextrin with a RAFT reagent

• Kohei Koyanagi,
• Yoshinori Takashima,
• Takashi Nakamura,
• Hiroyasu Yamaguchi and
• Akira Harada

Beilstein J. Org. Chem. 2016, 12, 2495–2502, doi:10.3762/bjoc.12.244

• generate the intermediate α-CD-CTA-Pn•. α-CD-CTA-Pn• is held in an equilibrium state with the macro-CTA, α-CD-CTA-Pn, and the benzyl radical (Bn•) with re-initiation activity. As demonstrated by the inhibition experiments, the yields and molecular weights of the polymers were affected by the molecular

Methylenelactide: vinyl polymerization and spatial reactivity effects

• Judita Britner and
• Helmut Ritter

Beilstein J. Org. Chem. 2016, 12, 2378–2389, doi:10.3762/bjoc.12.232

• -initiation beside AIBN initiation. Self-initiation of MLA The self-initiation of some non-cyclic push–pull monomers is already known [1]. However, up to now, the free radical self-initiation of cyclic MLA has not been described in the literature. Thus, we herewith show our postulated mechanism for the self

• -initiation of MLA in Scheme 2. We propose that a homolytically H–C cleavage takes place in a first step yielding two radicals. This process is accompanied by a change of hybridization from a tetrahedral sp3 structure of the chiral center to a trigonal planar sp2 structure of the resulting radical. Scheme 2

• -dioxane and dipolar DMF as solvents (Figure 5). Surprisingly, the yields of self-initiated polymerization in 1,4-dioxane are very similar to the yields of AIBN-initiated polymerization. In contrast, the self-initiation polymerization of MLA is much more retarded in DMF solution than in 1,4-dioxane. Taking

Enantioconvergent catalysis

• Justin T. Mohr,
• Jared T. Moore and
• Brian M. Stoltz

Beilstein J. Org. Chem. 2016, 12, 2038–2045, doi:10.3762/bjoc.12.192

• two enantioconvergent reactions, though related, must proceed through substantially different mechanisms of enantioinduction. The differential reactivity demonstrated by the enolate intermediate 22 highlights the power of accessing different mechanistic pathways via stereoablative initiation. Examples

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

Stimuli-responsive HBPS-g-PDMAEMA and its application as nanocarrier in loading hydrophobic molecules

• Yongsheng Chen,
• Li Wang,
• Haojie Yu,
• Zain-Ul-Abdin,
• Ruoli Sun,
• Guanghui Jing,
• Rongbai Tong and
• Zheng Deng

Beilstein J. Org. Chem. 2016, 12, 939–949, doi:10.3762/bjoc.12.92

• ) prepared through atom transfer radical self-condensing vinyl polymerization (AT-SCVP) was firstly reported in 1996 [26]. It used vinylbenzyl chloride (VBC), which is an important commercially available monomer and its industrial synthesis was started from 1957, as monomer with a self-initiation site [27

Diradical reaction mechanisms in [3 + 2]-cycloadditions of hetaryl thioketones with alkyl- or trimethylsilyl-substituted diazomethanes

• Grzegorz Mlostoń,
• Paulina Pipiak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2016, 12, 716–724, doi:10.3762/bjoc.12.71

• ]-cycloadditions via zwitterionic intermediates [8][9]. Large differences of energies of the frontier orbitals of dipole and dipolarophile, as well as sterically demanding groups at the terminus of the dipole, were pointed out as requirements for the initiation of the ‘zwitterionic pathway’. In addition to the

Antibiotics from predatory bacteria

• Juliane Korp,
• María S. Vela Gurovic and
• Markus Nett

Beilstein J. Org. Chem. 2016, 12, 594–607, doi:10.3762/bjoc.12.58

• transcription [106]. During early stages of transcriptional initiation, the RNAP clamp possesses an opened form in order to allow binding of the promoter DNA to the active-center cleft. At late transcriptional initiation and elongation, the clamp changes into a closed position to retain the DNA inside the

Biosynthesis of α-pyrones

• Till F. Schäberle

Beilstein J. Org. Chem. 2016, 12, 571–588, doi:10.3762/bjoc.12.56

• -related diseases, e.g., cancer [68]. A structurally related compound, i.e., isopimpinellin (63), was also first isolated from fruits of Ammi majus [69]. It was shown that 63 blocks DNA adduct formation and skin tumor initiation in mice [70]. Psoralen (64), isolated from plants, e.g., Ficus carica, had

Thermal and oxidative stability of Atlantic salmon oil (Salmo salar L.) and complexation with β-cyclodextrin

• Daniel I. Hădărugă,
• Mustafa Ünlüsayin,
• Alexandra T. Gruia,
• Cristina Birău (Mitroi),
• Gerlinde Rusu and
• Nicoleta G. Hădărugă

Beilstein J. Org. Chem. 2016, 12, 179–191, doi:10.3762/bjoc.12.20

• rate of α-linolenic acid (an omega-3 FA) is 2500 times higher in comparison with saturated stearic acid [15]. Light (photo-oxidation) and the presence of heavy metal ions, heme and hemin proteins or superoxide radical anion-generating enzymes are involved in the initiation of auto-oxidation. The main

Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands

• Julia Wappel,
• Roland C. Fischer,
• Luigi Cavallo,
• Christian Slugovc and
• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 154–165, doi:10.3762/bjoc.12.17

• average number molecular weight (Mn) can be used to characterize the ratio of initiation rate to propagation rate (ki/kp) of a given initiator to monomer combination [28][44][45][46]. Under the applied conditions (prolonged reaction time, reaction temperature up to 100 °C, UV-irradiation) none of the

• summarizes the results of the polymerization data, bearing substrate 5 (see Supporting Information File 1 for further details). Generally it can be concluded, that except of 4, the initiators show a relatively slow initiation compared to their propagation. The high molecular weights indicate a slow

N-Methylphthalimide-substituted benzimidazolium salts and PEPPSI Pd–NHC complexes: synthesis, characterization and catalytic activity in carbon–carbon bond-forming reactions

• Senem Akkoç,
• Yetkin Gök,
• İlhan Özer İlhan and
• Veysel Kayser

Beilstein J. Org. Chem. 2016, 12, 81–88, doi:10.3762/bjoc.12.9

• , 44280 Malatya, Turkey 10.3762/bjoc.12.9 Abstract A series of novel benzimidazolium salts (1–4) and their pyridine enhanced precatalyst preparation stabilization and initiation (PEPPSI) themed palladium N-heterocyclic carbene complexes [PdCl2(NHC)(Py)] (5–8), where NHC = 1-(N-methylphthalimide)-3

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

• -catalyzed oxyamination reaction remain unclear. In the control experiment with the absence of O-benzoylhydroxylamine, both carboxylic acid and olefin substrates were fully recovered, suggesting the critical role of O-benzoylhydroxylamine in the activation of copper catalyst for the initiation of this

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

• Krzysztof Skowerski,
• Jacek Białecki,
• Stefan J. Czarnocki,
• Karolina Żukowska and
• Karol Grela

Beilstein J. Org. Chem. 2016, 12, 5–15, doi:10.3762/bjoc.12.2

• ease of handling and product purification. Lower efficiency was observed in the case of catalyst supported on neutral aluminium oxide (8-Al2O3) which provided product 10 in diminished yield. On the other hand, the catalyst supported on unmodified silica gel (8-SiO2) showed the fastest initiation rate

New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand

• Agnieszka Hryniewicka,
• Szymon Suchodolski,
• Agnieszka Wojtkielewicz,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 2795–2804, doi:10.3762/bjoc.11.300

• catalysts 1 and 2 [23]. The introduction of a nitro group into the 6-position of the chromene moiety in catalyst 8 led to a decrease in the stability of the complex [22]. The aforementioned modifications concerned the benzylidene moiety of the catalysts and affected the initiation rate of the metathesis

• amounts of unreacted substrates. The high activity of Grela catalyst 3 was a result of faster initiation of the catalytic cycle arising from the electron-withdrawing effect of the nitro group. Consequently, lowered electron density at the oxygen atom in the isopropoxybenzylidene fragment weakens the

Pyridylidene ligand facilitates gold-catalyzed oxidative C–H arylation of heterocycles

• Kazuhiro Hata,
• Hideto Ito,
• Yasutomo Segawa and
• Kenichiro Itami

Beilstein J. Org. Chem. 2015, 11, 2737–2746, doi:10.3762/bjoc.11.295

• those with three catalysts (Figure 2a), (ii) the induction periods with regard to the formation of 3ba were found in the reactions using AuCl(PyC) and AuCl(PPh3) (Figure 2a,b), and (iii) the oxidant consumption began at the reaction initiation for all catalysts (Figure 2c). In the reaction using AuCl

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

• Stefan Naumann,
• Johannes Klein,
• Dongren Wang and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 2261–2266, doi:10.3762/bjoc.11.246

• 7-iPr-CO2 and 6-Cy-CO2 could be connected to a low initiation efficiency and consequently low ratio of propagating zwitterions to monomer, resulting in high-molecular weight polymers. In contrast, a sterically uncongested, highly nucleophilic NHC as liberated from 5Me-Me-CO2 (Table 1, entry 12) is

Half-sandwich nickel(II) complexes bearing 1,3-di(cycloalkyl)imidazol-2-ylidene ligands

• Johnathon Yau,
• Kaarel E. Hunt,
• Laura McDougall,
• Alan R. Kennedy and
• David J. Nelson

Beilstein J. Org. Chem. 2015, 11, 2171–2178, doi:10.3762/bjoc.11.235

• ) more quickly, which may be suggestive of faster initiation. Intrigued as to whether the more electron-donating nature of ICy and IDD, as inferred from their lower TEP [22][31], might influence their oxidative addition reactivity, the cross-coupling of 4’-chloroacetophenone and phenylboronic acid was

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

• band decreases and no new band appears in the range of 250–900 nm (Figure 3). If the irradiation of the sample is stopped for 1 min, the reaction halts, and the recorded UV spectrum exactly repeats the previous one. It might be suggested that the initiation step, excitation of 1 at 254 nm, leading to

Computational study of productive and non-productive cycles in fluoroalkene metathesis

• Markéta Rybáčková,
• Jan Hošek,
• Ondřej Šimůnek,
• Viola Kolaříková and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2015, 11, 2150–2157, doi:10.3762/bjoc.11.232

• include the initiation steps starting from metathesis precatalysts as Grubbs or Hoveyda–Grubbs 2nd generation precatalysts [15][16][17][18][19][20][21][22]. In contrast to common alkenes, the metathesis of fluoroalkenes has attracted far less attention [23]. Fluorinated modifications have mostly

• with selected fluoro- and chloroalkenes has been studied and the higher stability of a ruthenium intermediate containing a difluoromethylene ligand has been emphasized [36][37]. A complete mechanism of alkene metathesis including initiation, productive and non-productive cycles represents a highly

• . Moreover, the preference for non-productive cycles can hamper the formation of the desired product even in the absence of kinetic and thermodynamic issues (Scheme 1). At the beginning, the starting precomplex HG2 reacts in the initiation phase with alkene forming ruthenacyclobutane I, which releases 2

Ru complexes of Hoveyda–Grubbs type immobilized on lamellar zeolites: activity in olefin metathesis reactions

• Hynek Balcar,
• Naděžda Žilková,
• Martin Kubů,
• Michal Mazur,
• Zdeněk Bastl and
• Jiří Čejka

Beilstein J. Org. Chem. 2015, 11, 2087–2096, doi:10.3762/bjoc.11.225

• , but most probably with the slow initiation rate. If initiation starts by coordination of the substrate molecule to the Ru atom (association and interchange mechanism [36]), the steric conditions around the Ru atom may be important. The very low initiation rate with methyl oleate may implicate some

• restrictions in coordination of bulky molecules; we can speculate about some confinement in the coordination sphere of Ru in HGIIN+Cl−/MCM-22 (partial immersion of HGIIN+Cl− into support cavities and/or other deformation of the coordination sphere as a result of immobilization). When the initiation passed with

• was negligible and the reaction rate slightly exceeded that over HGIIN+Cl−/SBA-15. This behavior may indicate a slow initiation by methyl oleate due to its slow coordination to the Hoveyda–Grubbs type catalysts immobilized on the zeolite supports studied. Experimental Materials and techniques Ru

Supramolecular chemistry: from aromatic foldamers to solution-phase supramolecular organic frameworks

• Zhan-Ting Li

Beilstein J. Org. Chem. 2015, 11, 2057–2071, doi:10.3762/bjoc.11.222

• surface area. However, the achievement of periodicity is a challenge in solution for self-assembled architectures as a result of the impact of the solvent and the weakness of noncovalent forces that hold monomeric components together. In early 2012, I discussed the initiation of a project with Kangda

Olefin metathesis in air

• Lorenzo Piola,
• Fady Nahra and
• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2038–2056, doi:10.3762/bjoc.11.221

• , showed the highest rate of initiation reported to date for alkene metathesis reactions. Complex 81 is used mostly for ROMP and CM reactions with electron-deficient olefins. The complex can be prepared in air but only one example of its use in air has been reported. In 2010, Tew and co-workers reported

Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC) and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions

• Shawna L. Balof,
• K. Owen Nix,
• Matthew S. Olliff,
• Sarah E. Roessler,
• Arpita Saha,
• Kevin B. Müller,
• Ulrich Behrens,
• Edward J. Valente and
• Hans-Jörg Schanz

Beilstein J. Org. Chem. 2015, 11, 1960–1972, doi:10.3762/bjoc.11.212

• significantly improve the complex solubility in acidic aqueous media [32]. We have also demonstrated before that acid addition to (DMAP)2Ru–alkylidene complexes 6 and 7 resulted in fast protonation of the N-donor ligand and thus resulting in fast, irreversible and generally complete metathesis initiation [45

• ][46]. For most ROMP processes, this is desirable as a fast initiation typically affords high ROMP activity with low catalyst loadings [57][67]. Hence, hexacoordinate complexes 11 and 12 were also synthesized from their precursor complexes 9 and 10 [61] by ligand exchange according to Scheme 2. These

• complexes now contain pH-responsive groups at the H2ITap ligand to afford solubility in aqueous acid and at the N-donor ligand which affords rapid metathesis initiation. It should be noted that Plenio et al. also reported a Ru–benzylidene complex similar to catalysts 11 and 12 bearing the NEt2-analogue to

New aryloxybenzylidene ruthenium chelates – synthesis, reactivity and catalytic performance in ROMP

• Patrycja Żak,
• Szymon Rogalski,
• Mariusz Majchrzak,
• Maciej Kubicki and
• Cezary Pietraszuk

Beilstein J. Org. Chem. 2015, 11, 1910–1916, doi:10.3762/bjoc.11.206

• . Continuous efforts have been aimed at the search for new catalysts characterized by improved stability and catalytic performance. One of the current challenges is the development of catalysts allowing control of initiation for some metathesis polymerisation processes. For such applications a variety of

• latent catalysts have been reported which permit control of initiation and efficient propagation of the reaction [3][4][5]. Among numerous examples of latent catalysts, the complexes representing the structural motif illustrated in Figure 1 have been relative poorly investigated. Known examples include

Nitro-Grela-type complexes containing iodides – robust and selective catalysts for olefin metathesis under challenging conditions

• Andrzej Tracz,
• Mateusz Matczak,
• Katarzyna Urbaniak and
• Krzysztof Skowerski

Beilstein J. Org. Chem. 2015, 11, 1823–1832, doi:10.3762/bjoc.11.198

• anionic ligands. Grubbs et al. showed that the exchange of chlorides for bromides or iodides in the second generation Grubbs’ catalysts facilitated the initiation, but reduced the propagation rate and eventually provided no overall improvement [12]. More recently Slugovc et al. synthesized bromo- and iodo

• - analogues of HII, but no improvement was noted [13][14][15]. Moreover, the presence of iodide ligands reduced initiation rates for Hoveyda second generation complex bearing iodides (HII-I2) in ring-closing metathesis (RCM). Similarly, Schrodi and colleagues did not find any advantages for halide exchanged

• heterogenize catalysts, which resulted in the formation of materials with reduced activity and efficiency [23][24]. It is well recognized that the benzylidene ligand structure strongly influences initiation rates for Hoveyda-type catalysts [25]. As a consequence of the “boomerang effect”, which was recently