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Barbier,Bouveault
p. 1051
(1894)
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Aerobic oxidative dehydrogenations catalyzed by the mixed-addenda heteropolyanion PV2Mo10O405-: A kinetic and mechanistic study
The aerobic oxidative dehydrogenation of α-terpinene to p-cymene catalyzed by the mixed-addenda heteropolyanion PV2Mo10O405- has been used to investigate the oxidation mechanism catalyzed by this class of compounds. The kinetics of the reaction show it to be zero order in α-terpinene, first order in dioxygen, and second order in the heteropolyanion catalyst. The kinetic results along with the use of UV-vis, ESR, 31P NMR, and IR spectroscopy have enabled the formulation of a reaction scheme involving the formation of a stable substrate-catalyst complex in the catalyst reduction (substrate oxidation) stage and a μ-peroxo catalyst intermediate in the catalyst reoxidation where dioxygen is reduced to water in a four-electron redox reaction.
Neumann, Ronny,Levin, Michal
p. 7278 - 7286
(1992)
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Unexpected Superoxide Dismutase Antioxidant Activity of Ferric Chloride in Acetonitrile
The azobis(isobutyronitrile)-initiated autoxidation of γ-terpinene in acetonitrile at 50 °C yields onlyp-cymene and hydrogen peroxide (1:1) in a chain reaction carried by the hydroperoxyl radical, HOO. (Foti, M. C.; Ingold, K. U. J. Agric. Food Chem. 2003, 51, 2758-2765). This reaction is retarded by very low (μM) concentrations of FeCl3 and CuCl 2. The kinetics of the FeCl3-inhibited autoxidation are consistent with chain-termination via the following: Fe3+ + HOO . ? [FeIV-OOH]3+ and [Fe IV-OOH]3+ + HOO. → Fe3+ + H2O2 + O2. Thus, FeCl3 in acetonitrile can be regarded as a very effective (and very simple) superoxide dismutase. The kinetics of the CuCl2-inhibited autoxidation indicate that chain transfer occurs and becomes more and more important as the reaction proceeds, i.e., the inhibition is replaced by autocatalysis. These kinetics are consistent with-reduction of Cu2+ to Cu+ by HOO . and then the reoxidation of Cu+ to Cu2+ by both HOO. and the H2O2 product. The latter reaction yields HO. radicals which continue the chain.
Foti, Mario C.,Ingold
p. 9162 - 9165
(2003)
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Ipatieff,Pines,Olberg
p. 694,695
(1945)
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The effect of UTL layer connectivity in isoreticular zeolites on the catalytic performance in toluene alkylation
Toluene alkylation with isopropyl alcohol was used as a model reaction to investigate the effect of UTL-type layer connectivity in a series of isoreticular zeolites and related zeolitic materials. All prepared catalysts possess the same structure of the layers but their connectivity differs from amorphous pillars (IPC-1PI), double-four-rings (UTL), single-four-rings (IPC-2?=?OKO, International Zeolite Association code), oxygen bridges (IPC-4?=?PCR), or their combinations (IPC-6 and IPC-7). X-ray powder diffraction, scanning electron microscopy, and nitrogen adsorption isotherms were employed to characterize structural and textural properties of the studied catalysts. Deuterated acetonitrile was adsorbed on catalysts to determine the concentrations and type of individual acid sites. Toluene alkylation with isopropyl alcohol evidenced that toluene conversion increases with increasing size of zeolite channels. Simultaneously, selectivity in cymenes increased as open structure of these catalysts did not present optimum reaction volume for the bimolecular reaction of cymenes with toluene to n-propylbenzenes.
?ilková, Nadě?da,Eliá?ová, Pavla,Al-Khattaf, Sulaiman,Morris, Russell E.,Mazur, Michal,?ejka, Ji?í
p. 55 - 60
(2016)
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Ipatieff,Pines
p. 1226
(1945)
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Dodge
p. 561
(1890)
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Photooxidation of a conjugated diene by an exciplex mechanism: Amplification via radical chain reactions in the perylene diimide-photosensitized oxidation of α-terpinene
Irradiation of the perylene diimide (1) or 9,10-dicyanoanthracene (DCA) in the presence of α-terpinene (2-HH) in the presence of molecular oxygen leads to moderately efficient oxidation of 2-HH to p-cymene (2). Although 1 might be expected to photosensitize oxidations by the conventional "singlet oxygen pathways, spectroscopic studies indicate that while oxygen can quench the fluorescent singlet of 1, no singlet oxygen is produced. 2-HH is also an efficient quencher of the fluorescent singlets of 1 and DCA and, for nonpolar solvents such as methylene chloride, in each case the quenching results in formation of an exciplex or contact radical ion pair. Under conditions where quenching by 2-HH to form the exciplex is complete, maximum quantum yields of 2 are obtained, thus indicating that the exciplex is the precursor to its formation. Nonproductive decay of the exciplex to starting materials is its major fate, thus the moderately high quantum efficiencies for formation of 2 require a mechanism involving amplification. Spin-trapping experiments suggest the role of hydroperoxy radicals and amplification by a radical chain mechanism involving these radicals and the intermediate 2-H. is proposed. Possible paths for reaching these radicals from the exciplex are considered; either oxygen quenching of the exciplex or proton transfer within the exciplex followed by oxygen interception of the semireduced perylene diimide appear viable. For the reaction of DCA with 2-HH and oxygen, it is found that the much longer-lived exciplex undergoes quenching by oxygen.
Chen, Liaohai,Lucia, Lucian A.,Gaillard,Whitten, David G.,Icil,Icli
p. 9095 - 9098
(1998)
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New insight into solvent effects on the formal HOO. + HOO . reaction
The 2,2′-azobis(isobutyronitrile)(AIBN)-induced autoxidation of γ-terpinene (TH) at 50°C produces p-cymene and hydrogen peroxide in a radical-chain reaction having HOO. as one of the chain-carrying radicals. The kinetics of this reaction in cyclohexane and teri-butyl alcohol show that chain termination involves the formal HOO. + HOO . self-reaction over a wide range of γ-terpinene, AIBN, and O2 concentrations. However, in acetonitrile this termination process is accompanied by termination via the cross-reaction of the terpinenyl radical, T., with the HOO. radical under conditions of relatively high [TH] (140-1000 mM) and low [O2] (2.0-5.5 mM). This is because the formal HOO. + HOO. reaction is comparatively slow in acetonitrile (2k～8×107 M-1 s-1), whereas, this reaction is almost diffu-sion-controlled in tert-butyl alcohol and cyclohexane, 2k～6.5×108 and 1.3×109 M-1 s-1 respectively. Three mechanisms for the bimolecular self-reaction of HOO. radicals are considered: 1) a head-to-tail hydrogen-atom transfer from one radical to the other, 2) a head-to-head reaction to form an intermediate tetroxide, and 3) an electrontransfer between HOO . and its conjugate base, the superoxide radical anion, O 2-.. The rate constant for reaction by mechanism (1) is shown to be dependent on the hydrogen bond (HB) accepting ability of the solvent; that by mechanism (2) is shown to be too slow for this process to be of any importance; and that by mechanism (3) is de-pendent on the pH of the solvent and its ability to support ionization. Mechanism (3) was found to be the main termination process in tert-butyl alcohol and acetonitrile. In the gas phase, the rate constant for the HOO. + HOO. reaction (mechanism (1)) is about 1.8× 109 M-1 s-1 but in water at pH ≤2 where the ionization of HOO. is completely suppressed, this rate constant is only 8.6×105 M-1 s-1. The very large retarding effect of water on this reaction has not previously been explained. We find that it can be quantitatively accounted for by using Abraham's HB acceptor parameter, β2H, for water of 0.38 and an estimated HB donor parameter, α2 H, for HOO. of about 0.87. These Abraham parameters allow us to predict a rate constant for the HOO. + HOO. reaction in water at 25°C of 1.2×106 M-1 s-1 in excellent agreement with experiment.
Foti, Mario C.,Sortino, Salvatore,Ingold
p. 1942 - 1948
(2005)
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Mechanism of inhibition of lipid peroxidation by γ-terpinene, an unusual and potentially useful hydrocarbon antioxidant
γ-Terpinene (TH), a monoterpene hydrocarbon present in essential oils, retards the peroxidation of linoleic acid (LH). The peroxidation of TH has been shown to yield p-cymene as the only organic product in a chain reaction in which the chain carrier is the hydroperoxyl radical, HOO.. The peroxidation of LH is well-known to be a chain reaction in which the chains are carried by linoleylperoxyl radicals, LOO., and the products are linoleyl hydroperoxides. The retardation of LH peroxidation by TH has been found to be due to rapid chain termination via a very fast cross-reaction between HOO. and LOO. radicals. This antioxidant mechanism is completely different from the mechanism of antioxidant action of vitamin E. Since vitamin E becomes a prooxidant at high concentrations, the addition of essential oils containing TH to edible lipids may provide an alternative or supplementary strategy for obtaining large increases in their oxidative stability and shelf life, something that cannot be achieved by simply adding more and more vitamin E.
Foti, Mario C.,Ingold
p. 2758 - 2765
(2003)
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The conversion of 1,8-cineole sourced from renewable Eucalyptus oil to p-cymene over a palladium doped γ-Al2O3 catalyst
The conversion of 1,8-cineole, sourced from the steam distillation of Eucalyptus waste, to p-cymene has been studied. Both alumina and palladium on alumina have been found to be active catalysts, the latter producing p-cymene in near quantitative conversion. Catalyst testing coupled with catalyst characterisation showed the catalysts to be multifunctional, promoting dehydration, dehydrogenation and isomerisation in a one step process.
Leita, Benjamin A.,Gray, Peter,O'Shea, Mike,Burke, Nick,Chiang, Ken,Trimm, David
p. 98 - 102
(2011)
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Absolute rate constants and transient intermediates in the free-radical-induced peroxidation of γ-terpinene, an unusual hydrocarbon antioxidant
The peroxidation of γ-terpinene (TH) initiated by tert-butoxyl radicals has been investigated by means of nanosecond laser flash photolysis techniques in acetonitrile at room temperature. The absolute rate constants for the reactions implicated in the peroxidation process have been determined and the main short-lived intermediates, terpenyl and terpenylperoxyl radicals, have been detected. The rate constant for H-atom abstraction from TH by tert-butoxyl radicals, K3, has been found to be 1.4 × 108 M -1 s-1 while the values for the self-quenching of T? radicals, 2k4, and the addition of O2 to T? k 9, are, respectively, 1.2 × 1010 M-1 s-1 and 1.3 × 109 M-1 s-1. The overall results strongly substantiate the peroxidation mechanism recently proposed by Foti and Ingold, J. Agric. Food Chem., 2003, 51, 2758, and provide a solid basis for a better understanding of the unusual antioxidant activity exhibited by this hydrocarbon.
Sortino, Salvatore,Petralia, Salvatore,Foti, Mario C.
p. 1563 - 1567
(2003)
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Deactivation of a ruthenium(II) N-heterocyclic carbene p-cymene complex during transfer hydrogenation catalysis
A ruthenium (II) N-heterocyclic carbene (NHC) complex was synthesized to investigate ligand dissociation as a possible deactivation pathway for the catalytic cycle of a transfer hydrogenation reaction. Diiodo(1,3-dimethylbenzimidazole-2-ylidene)(p-cymene)ruthenium(II) was synthesized for use as the catalytic species and characterized using physico-chemical, spectroscopic methods, and single crystal X-ray diffraction. The transfer of hydrogen from isopropanol to acetophenone was followed using 1H NMR. We observed 94% conversion of the substrate to the alcohol product after 1?h. We also found that the p-cymene complex decomposed during the catalytic reaction to the extent of 80% deactivation after 1?h, based on 1H NMR spectrometry. From Gaussian calculations, an ultraviolet–visible spectrum that is in excellent agreement with the actual spectrum was computed, giving insight into the nature of the absorptions observed experimentally.
Miecznikowski, John R.,Bernier, Nicholas A.,Van Akin, Christopher A.,Bonitatibus, Sheila C.,Morgan, Maura E.,Kharbouch, Rami M.,Mercado, Brandon Q.,Lynn, Matthew A.
p. 21 - 29
(2018)
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Solvent-free dehydrogenation of γ-terpinene in a ball mill: Investigation of reaction parameters
The present article reports on the solvent-free dehydrogenation of γ-terpinene (1) in a planetary ball mill affording p-cymene (2) as the predominant reaction product. The influence of various reaction parameters and technical variables on the transformation of 1 has been assessed. Thus, it is shown that KMnO4 can be substituted by other, less-toxic and environmentally-benign oxidation agents (Oxone, NaIO4, I 2). In most cases the reaction yielded 2 with high selectivities, whereby conversion can be fine-tuned by variation of the oxidant-to-substrate ratio, the rotation frequency νrot, the number of milling balls nball or the type of grinding auxiliary employed. Contrary to particle refinement processes, the size of the milling balls d (constant mass) has no influence on the conversion and chemical yield. The Royal Society of Chemistry 2010.
Szuppa, Tony,Stolle, Achim,Ondruschka, Bernd,Hopfe, Wieland
p. 1288 - 1294
(2010)
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Alkylation of Toluene with Isopropanol on Lantanum Modified ZSM-5 Zeolite
Abstract: The effect of lanthanum concentration on the physicochemical and catalyticproperties of HZSM-5 zeolite in a reaction of toluene alkylation withisopropanol was studied in a temperature range of 250–350°C. Based on the dataobtained by X-ray diffraction analysis, low-temperature nitrogen adsorption (BETmethod), and IR spectroscopy, it was shown that an increase in lanthanumconcentration in HZSM-5 from 1.0 wt % to 7.0 wt % reduces both the specificsurface area and the pore volume of the zeolite despite the retention of itscrystalline structure. This also results in redistribution of acid sites,specifically decreases the concentration of strong Br?nsted acid sites (B) andincreases that of moderate Lewis acid sites (L), thus decreasing the B/L ratiofrom 3.53 to 0.20. All these occurrences have a crucial effect on theselectivity of reaction products and, in particular, on the p-isopropyl toluene (4-IPT) selectivity. Maximumselectivity, making up 72.4%, is achieved by a zeolite containing 5.0 wt %lanthanum at a B/L ratio of 0.25.
Abdullaeva,Voskressenskii,Akhmedova,Mamedov
p. 190 - 197
(2020/12/17)

Mesoporous tin phosphate as an effective catalyst for fast cyclodehydration of bio-based citral into p-cymene
Effective synthesis of aromatic compounds from renewable biomass is highly important yet challenging. p-Cymene is an attractive aromatic compound with various promising applications in the manufacture of fine chemicals. In this study, a novel and effective catalytic system based on mesoporous tin phosphate (M-SnPO) with Lewis-Br?nsted dual acidity was developed for the fast synthesis of p-cymene from the cyclodehydration of bio-based citral. Up to 78.5% yield of p-cymene was achieved from the cyclodehydration of citral at 180 °C within only 0.5 h, superior to the results reported for benchmark homogeneous acid catalysts. Characterization of as-prepared M-SnPO catalyst via various techniques indicates that the synergic effect of Lewis and Br?nsted acidic sites, large pore-sized structure, and high surface area are responsible for its remarkable catalytic performance. In addition, the effectiveness of the M-SnPO catalyst could be almost sustained over multiple cycles without significant loss. The work herein is the first example of developing a Lewis-Br?nsted dual acidic heterogeneous catalyst for the fast synthesis of p-cymene from the cyclodehydration of citral.
He, Jian,Li, Hu,Wu, Hongguo,Yang, Song,Yu, Zhaozhuo
(2021/09/28)

Radical induced disproportionation of alcohols assisted by iodide under acidic conditions
The disproportionation of alcohols without an additional reductant and oxidant to simultaneously form alkanes and aldehydes/ketones represents an atom-economical transformation. However, only limited methodologies have been reported, and they suffer from a narrow substrate scope or harsh reaction conditions. Herein, we report that alcohol disproportionation can proceed with high efficiency catalyzed by iodide under acidic conditions. This method exhibits high functional group tolerance including aryl alcohol derivatives with both electron-withdrawing and electron-donating groups, furan ring alcohol derivatives, allyl alcohol derivatives, and dihydric alcohols. Under the optimized reaction conditions, a 49% yield of 5-methyl furfural and a 49% yield of 2,5-diformylfuran were obtained simultaneously from 5-hydroxymethylfurfural. An initial mechanistic study suggested that the hydrogen transfer during this redox disproportionation occurred through the inter-transformation of HI and I2. Radical intermediates were involved during this reaction.
Huang, Yang,Jiang, Haiwei,Li, Teng,Peng, Yang,Rong, Nianxin,Shi, Hexian,Yang, Weiran
supporting information
p. 8108 - 8115
(2021/10/29)

Halogen-Bridged Methylnaphthyl Palladium Dimers as Versatile Catalyst Precursors in Coupling Reactions
Halogen-bridged methylnaphthyl (MeNAP) palladium dimers are presented as multipurpose Pd-precursors, ideally suited for catalytic method development and preparative organic synthesis. By simply mixing with phosphine or carbene ligands, they are in situ converted into well-defined monoligated complexes. Their catalytic performance was benchmarked against state-of-the-art systems in challenging Buchwald–Hartwig, Heck, Suzuki and Negishi couplings, and ketone arylations. Their use enabled record-setting activities, beyond those achievable by optimization of the ligand alone. The MeNAP catalysts permit syntheses of tetra-ortho-substituted arenes and bulky anilines in near-quantitative yields at room temperature, allow mono-arylations of small ketones, and enable so far elusive cross-couplings of secondary alkyl boronic acids with aryl chlorides.
Doppiu, Angelino,Goo?en, Lukas J.,Hu, Zhiyong,Pirkl, Nico,Sivendran, Nardana
supporting information
p. 25151 - 25160
(2021/10/19)

Preparation of α-terpineol and perillyl alcohol using zeolites beta
The preparation of α-terpineol by direct hydration of limonene catalyzed by zeolites beta was studied. The same catalyst was used to prepare perillyl alcohol by isomerization of β-pinene oxide in the presence of water. The aim was to optimize the reaction conditions to achieve high conversions of starting material and high selectivity to the desired products. In the case of limonene, it was found that the highest selectivity to α-terpineol was 88% with conversion of 36% under the conditions: 50?wt% of catalyst beta 25, 10% aqueous acetic acid (10?mL) (volume ratio limonene:H2O = 1:4.5), temperature 50?°C, after 24?h. In the case of β-pinene oxide, it was found that the highest selectivity to perillyl alcohol, which was 36% at total conversion, was obtained in the reaction under the following conditions: dimethyl?sulfoxide as solvent (volume ratio β-pinene oxide:DMSO = 1:5), catalyst beta 25 without calcination (15?wt%), demineralized water (molar ratio β-pinene oxide:H2O = 1:8), temperature 70?°C, 3?h. The present study shows that the studied reactions are suitable for the selective preparation of chosen compounds.
?erveny, Libor,Vysko?ilová, Eli?ka,Zítová, Kate?ina
p. 4297 - 4310
(2021/07/26)

Singlet-Oxygen Generation by Peroxidases and Peroxygenases for Chemoenzymatic Synthesis
Singlet oxygen is a reactive oxygen species undesired in living cells but a rare and valuable reagent in chemical synthesis. We present a fluorescence spectroscopic analysis of the singlet-oxygen formation activity of commercial peroxidases and novel peroxygenases. Singlet-oxygen sensor green (SOSG) is used as fluorogenic singlet oxygen trap. Establishing a kinetic model for the reaction cascade to the fluorescent SOSG endoperoxide permits a kinetic analysis of enzymatic singlet-oxygen formation. All peroxidases and peroxygenases show singlet-oxygen formation. No singlet oxygen activity could be found for any catalase under investigation. Substrate inhibition is observed for all reactive enzymes. The commercial dye-decolorizing peroxidase industrially used for dairy bleaching shows the highest singlet-oxygen activity and the lowest inhibition. This enzyme was immobilized on a textile carrier and successfully applied for a chemical synthesis. Here, ascaridole was synthesized via enzymatically produced singlet oxygen.
Ingenbosch, Kim N.,Quint, Stephan,Dyllick-Brenzinger, Melanie,Wunschik, Dennis S.,Kiebist, Jan,Süss, Philipp,Liebelt, Ute,Zuhse, Ralf,Menyes, Ulf,Scheibner, Katrin,Mayer, Christian,Opwis, Klaus,Gutmann, Jochen S.,Hoffmann-Jacobsen, Kerstin
p. 398 - 407
(2020/10/09)

Novel palladium nanoparticles supported on mesoporous natural phosphate: Catalytic ability for the preparation of aromatic hydrocarbons from natural terpenes
Various ratios of palladium nanoparticles supported on mesoporous natural phosphate (Pd@NP) were prepared using the wetness impregnation method. The prepared catalysts were characterized by IR, XRD, CV, SEM, EDX, XRF, TEM and BET analysis. The reduction and preparation of the palladium nanoparticles afford a crystallite size of 10.88 nm. The performance of the synthesized catalyst was investigated in the solvent-free dehydroaromatization of α-, β- and γ-himachalene mixture from Cedrus atlantica oil as a model substrate. In order to achieve an efficient and selective catalysis, the catalytic dehydroaromatization of various terpenes such as limonene, limonaketone, carvone, carveol and perillyl alcohol was studied. The Pd@NP catalyst performed a high catalytic activity, selectivity and recyclability in the terpenes dehydroaromatization reaction.
Mekkaoui, Ayoub Abdelkader,Aberkouks, Abderrazak,Fkhar, Lahcen,Ait Ali, Mustapha,El Firdoussi, Larbi,El Houssame, Soufiane
(2020/07/24)

Photochemical generation of acyl and carbamoyl radicals using a nucleophilic organic catalyst: Applications and mechanism thereof
We detail a strategy that uses a commercially available nucleophilic organic catalyst to generate acyl and carbamoyl radicals upon activation of the corresponding chlorides and anhydrides via a nucleophilic acyl substitution path. The resulting nucleophilic radicals are then intercepted by a variety of electron-poor olefins in a Giese-type addition process. The chemistry requires low-energy photons (blue LEDs) to activate acyl and carbamoyl radical precursors, which, due to their high reduction potential, are not readily prone to redox-based activation mechanisms. To elucidate the key mechanistic aspects of this catalytic photochemical radical generation strategy, we used a combination of transient absorption spectroscopy investigations, electrochemical studies, quantum yield measurements, and the characterization of key intermediates. We identified a variety of off-the-cycle intermediates that engage in a light-regulated equilibrium with reactive radicals. These regulated equilibriums cooperate to control the overall concentrations of the radicals, contributing to the efficiency of the overall catalytic process and facilitating the turnover of the catalyst. This journal is
Balletti, Matteo,De Pedro Beato, Eduardo,Mazzarella, Daniele,Melchiorre, Paolo
p. 6312 - 6324
(2020/08/24)

Photocatalytic Molecular Oxygen Activation by Regulating Excitonic Effects in Covalent Organic Frameworks
Excitonic effects caused by Coulomb interactions between electrons and holes play subtle and significant roles on photocatalysis, yet have been long ignored. Herein, porphyrinic covalent organic frameworks (COFs, specifically DhaTph-M), in the absence or presence of different metals in porphyrin centers, have been shown as ideal models to regulate excitonic effects. Remarkably, the incorporation of Zn2+ in the COF facilitates the conversion of singlet to triplet excitons, whereas the Ni2+ introduction promotes the dissociation of excitons to hot carriers under photoexcitation. Accordingly, the discriminative excitonic behavior of DhaTph-Zn and DhaTph-Ni enables the activation of O2 to 1O2 and O2?-, respectively, under visible light irradiation, resulting in distinctly different activity and selectivity in photocatalytic terpinene oxidation. Benefiting from these results, DhaTph-Ni exhibits excellent photocatalytic activity in O2?-engaged hydroxylation of boronic acid, while DhaTph-Zn possesses superior performance in 1O2-mediated selective oxidation of organic sulfides. This work provides in-depth insights into molecular oxygen activation and opens an avenue to the regulation of excitonic effects based on COFs.
Qian, Yunyang,Li, Dandan,Han, Yulan,Jiang, Hai-Long
p. 20763 - 20771
(2020/12/23)

Recyclable Ruthenium Catalyst for Distal meta-C?H Activation
We disclose the unprecedented hybrid-ruthenium catalysis for distal meta-C?H activation. The hybrid-ruthenium catalyst was recyclable, as was proven by various heterogeneity tests, and fully characterized with various microscopic and spectroscopic techniques, highlighting the physical and chemical stability. Thereby, the hybrid-ruthenium catalysis proved broadly applicable for meta-C?H alkylations of among others purine-based nucleosides and natural product conjugates. Additionally, its versatility was further reflected by meta-C?H activations through visible-light irradiation, as well as para-selective C?H activations.
Choi, Isaac,Müller, Valentin,Wang, Yanhui,Xue, Kai,Kuniyil, Rositha,Andreas, Loren B.,Karius, Volker,Alauzun, Johan G.,Ackermann, Lutz
supporting information
p. 15290 - 15297
(2020/10/26)

Insights into Ruthenium(II/IV)-Catalyzed Distal C?H Oxygenation by Weak Coordination
C?H hydroxylation of aryl acetamides and alkyl phenylacetyl esters was accomplished via challenging distal weak O-coordination by versatile ruthenium(II/IV) catalysis. The ruthenium(II)-catalyzed C?H oxygenation of aryl acetamides proceeded through C?H ac
Bu, Qingqing,Kuniyil, Rositha,Shen, Zhigao,Gońka, El?bieta,Ackermann, Lutz
supporting information
p. 16450 - 16454
(2020/11/02)

An entirely solvent-free photooxygenation of olefins under continuous flow conditions
Photooxygenations of alkenes with singlet oxygen are a versatile, atom-economical transformation. The choice of solvents is key to the success of this oxyfunctionalization with direct impact on the solubility of substrates, the lifetime of the reactive oxygen species, and the up-scaling of the process. We report an entirely solvent-free continuous-flow photooxygenation that operates at very high substrate/sensitizer ratios and enables high space-time yields.
Bayer, Patrick,Jacobi Von Wangelin, Axel
p. 2359 - 2364
(2020/05/28)

Synthesis of isobenzofuran derivatives from renewable 2-carene over halloysite nanotubes
Condensation of a terpene 2-carene with 4-methoxybenzaldehyde over a range of acid aluminosilicates including halloysite nanotubes (HNT) was studied for as a model for preparation of isobenzofuran derivatives with a pharmaceutical potential. The catalysts were characterized by FTIR with pyridine, UV by adsorption of 2-phenylethylamine from the aqueous phase, SEM, TEM and N2 physisorption. The largest selectivity to the desired product (ca. 70%) over halloysite nanotubes is associated with weak acidity of these catalysts (45 μmol/g), allowing avoiding side isomerization and condensation reactions. Moreover, the highest yield on air-dry HNT clearly indicates that weak Br?nsted sites favored the reaction. On the contrary, over strong Br?nsted and Lewis acids (Amberlyst-15, scandium triflate), the yield of isobenzofurans did not exceed 16% with formation of mainly 2-carene isomerization products. DFT calculations showed that interactions of the aldehyde with cyclopropane moiety of 2-carene giving isobenzofurans are more beneficial than an alternative direct attack of a proton, leading to side reactions. A possibility to reuse of HNT catalyst was confirmed. Overall, halloysite is a highly effective catalyst for production of isobenzofuran compounds based on 2-carene.
Agabekov, V. E.,Aho, A.,Il'ina, I. V.,Korchagina, D. V.,Kravtsova, A. V.,Li-Zhulanov, N. S.,M?ki-Arvela, P.,Murzin, D. Yu.,Salakhutdinov, N. F.,Sandberg, T.,Sidorenko, A. Yu.,Volcho, K. P.
(2020/05/08)

Conjugating Biotin to Ruthenium(II) Arene Units via Phosphine Ligand Functionalization
Two-step functionalization of 4-diphenylphosphino benzoic acid with biotin afforded 2-(biotinyloxy)ethyl 4-(diphenylphosphanyl)benzoate (LP), that was subsequently used to synthesize the Ru(II) arene complexes [RuCl2(η6-p-cymene)(LP)] (1), [Ru(C2O4)(η6-p-cymene)(LP)] (2) and [Ru(curc)(η6-p-cymene)(LP)]NO3 ([3]NO3), the latter incorporating curcumin (curcH) as an additional bioactive fragment. [Ru(curc)(η6-p-cymene)(PPh3)]NO3 ([4]NO3) was also prepared as a reference compound. Compounds 2 and [3]NO3 exhibited excellent stability in water/DMSO solution while being slowly activated in the cell culture medium over 72 hours. Together with LP, they were therefore assessed for their antiproliferative activity towards a panel of cancer cell lines, with different levels of biotin transporter expression. The apparent affinity of the compounds towards avidin varies, and their antiproliferative activity does not correlate with biotin transporter expression, although it is systematically enhanced when biotin-free cell culture medium is used.
B?au?, Andrzej,Batchelor, Lucinda K.,Biancalana, Lorenzo,Dyson, Paul J.,Grucha?a, Martyna,Marchetti, Fabio,Monti, Andrea,Pampaloni, Guido,Rychlik, B?a?ej
supporting information
p. 1061 - 1072
(2019/11/14)

Partial and Total Solvent-Free Limonene's Hydrogenation: Metals, Supports, Pressure, and Water Effects
Bio-based solvents menthene and menthane were obtained through limonene's partial and total hydrogenation under various catalytic conditions. Heterogeneous catalysts based on different active metals and supports (carbon, alumina, and silica) were systematically tested for solvent-free total and partial hydrogenation of limonene under high and low hydrogen pressure. Influences of these catalysts on the formation of menthene, menthane, and cymene, a dehydrogenated product, were determined. The impact of water addition on the conversion and selectivity of the catalysts was also investigated. Amongst all tested catalysts, Rh/Alumina which was never tested for total and partial hydrogenation of limonene was the most effective as 1-menthene was quantitatively produced at low pressure (0.275 MPa) while menthane was mostly obtained at a higher pressure (2.75 MPa). Water addition on Rh/Alumina favoured menthene production even at high pressure. To propose menthane, menthene, and menthane/menthene mixture as an alternative to fossil-based solvents such as n-hexane for the extraction of natural products, β-carotene, vanillin, and rosmarinic acid solubilizations have been investigated. If a modeling approach using COSMO-RS software predicted a comparable solubilization of these 3 compounds for the 3 solvents, experimental assays revealed that menthene solubilizes β-carotene, vanillin, and rosmarinic acid three to five times better than n-hexane.
Chemat, Farid,Clarisse, Olivier,Fabiano-Tixier, Anne-Sylvie,Ndongou Moutombi, Fanta J.,Touaibia, Mohamed
(2020/04/27)

Engineering a Highly Defective Stable UiO-66 with Tunable Lewis-Br?nsted Acidity: The Role of the Hemilabile Linker
The stability of metal-organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to a maximum of six defects per cluster in UiO-66. We synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects but also as a coligand that enhances the stability of the resulting defective framework. Furthermore, upon a postsynthetic treatment in H2SO4, the average number of defects increases to the optimum of six missing BDC linkers per cluster (three per formula unit), leaving the Zr-nodes on average sixfold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Br?nsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Br?nsted acid sites, the Hl-UiO-66 and the postsynthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD3CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Br?nsted to Lewis acid ratio in the materials and thus their catalytic activity and selectivity.
De Geyter, Nathalie,De Vos, Dirk E.,Feng, Xiao,Hajek, Julianna,Hoffman, Alexander E. J.,Jena, Himanshu Sekhar,Leus, Karen,Leyssens, Karen,Marquez, Carlos,Meynen, Vera,Morent, Rino,Van Der Voort, Pascal,Van Speybroeck, Veronique,Veerapandian, Savita K. P.,Wang, Guangbo
p. 3174 - 3183
(2020/03/10)

Robust Organic Photosensitizers Immobilized on a Vinylimidazolium Functionalized Support for Singlet Oxygen Generation under Continuous-Flow Conditions
Rose Bengal was immobilized on a vinylimidazolium functionalized support, and the heterogeneous organic photosensitizer thus prepared was applied for photooxidation reactions of organic molecules under continuous-flow conditions. Substituents of the cation part of the support were found to play a crucial role in determining the lifetime of the catalyst. More than 11 days continuous operation of a flow reaction was achieved.
Kobayashi, Shū,Koumura, Nagatoshi,Masuda, Koichiro,Onozawa, Shun-Ya,Sato, Kazuhiko,Shimada, Shigeru,Wang, Yao
supporting information
p. 497 - 501
(2020/03/13)

Ruthenium(II) Porphyrin Quinoid Carbene Complexes: Synthesis, Crystal Structure, and Reactivity toward Carbene Transfer and Hydrogen Atom Transfer Reactions
Reactivity study of novel metal carbene complexes can offer new opportunities in catalytic carbene transfer reactions as well as in other synthetic protocols. Metal complexes with quinoid carbene (QC) ligands are assumed to be key intermediates in a variety of metal-catalyzed QC transfer reactions using diazo quinones, which demands development of the chemistry of QC transfer of well characterized metal-QC complexes. Herein we report the isolation and QC transfer of ruthenium porphyrins [Ru(Por)(QC)] which contribute the first examples of (i) structurally characterized metal-QC complex (by X-ray crystallography) and (ii) isolated metal-QC complex that undergoes QC transfer reaction. The complexes [Ru(Por)(QC)] were prepared from reaction of [Ru(Por)(CO)] with diazo quinones and exhibited dual reactivity, i.e., hydrogen atom transfer (HAT) as well as QC transfer. The stoichiometric QC transfer reactions from these Ru-QC complexes to nitrosoarenes (ArNO) afforded nitrones in up to 90% yield, and the corresponding catalytic reactions were also developed. Both the stoichiometric and catalytic reactions for a series of QC ligands bearing electron-donating and -withdrawing substituents showed a reverse substituent effect on the QC transfer reactivity. Complexes [Ru(Por)(QC)] are also reactive toward C-H and X-H (X = N, S) bonds and can catalyze aerobic oxidation of 1,4-cyclohexadiene; their stoichiometric HAT reactions with unsaturated hydrocarbons gave product yields of up to 88%. The unique dual reactivity and electronic feature of [Ru(Por)(QC)] were studied by spectroscopic means and density functional theory (DFT) calculations.
Wang, Hai-Xu,Wan, Qingyun,Wu, Kai,Low, Kam-Hung,Yang, Chen,Zhou, Cong-Ying,Huang, Jie-Sheng,Che, Chi-Ming
supporting information
p. 9027 - 9046
(2019/06/13)

Novel approach towards Al-rich AFI for catalytic application
A new germanosilicate structural analogue of AFI zeolite (Ge-AFI) was hydrothermally synthesized. One- and two-step alumination of the Ge-AFI zeolites were used to modify their structure and acidic properties traced using XRD, N2 adsorption, ICP-OES, 27Al NMR, and FTIR spectroscopy. Two-step aluminated sample (deGe-Al-AFI) provided a higher Al content, stronger acid sites and a higher micropore volume than one-step aluminated sample (Al-AFI). Extensive evaluation of the catalytic performance of these AFI zeolites compared with reference conventional zeolite catalysts for alkylation of toluene with isopropyl alcohol showed that deGe-Al-AFI exhibited relatively high toluene conversion and selectivity to valuable p-cymene due to the optimized textural and acidic properties.
Zhou, Yong,?ilková, Nadě?da,Shamzhy, Mariya,Avadhut, Yamini,Hartmann, Martin,?ejka, Ji?í,Opanasenko, Maksym
p. 62 - 68
(2019/04/01)

Arene-Free Ruthenium(II/IV)-Catalyzed Bifurcated Arylation for Oxidative C?H/C?H Functionalizations
Experimental and computational studies provide detailed insight into the selectivity- and reactivity-controlling factors in bifurcated ruthenium-catalyzed direct C?H arylations and dehydrogenative C?H/C?H functionalizations. Thorough investigations revealed the importance of arene-ligand-free complexes for the formation of biscyclometalated intermediates within a ruthenium(II/IV/II) mechanistic manifold.
Rogge, Torben,Ackermann, Lutz
supporting information
p. 15640 - 15645
(2019/10/28)

Synthesis, Stability, and (De)hydrogenation Catalysis by Normal and Abnormal Alkene- And Picolyl-Tethered NHC Ruthenium Complexes
A series of p-cymene and cyclopentadienyl Ru(II)-aNHC complexes were synthesized from 2-methylimidazolium salts with either an N-bound alkenyl (1, 3) or picolyl tether (6, 7). The C(5)-Me substituted alkenyl-tethered analogues (2, 4) were also synthesized. Ag-mediated C(2)-dealkylation was a prominent side reaction that led to the formation of normally bound NHC Ru(II) complexes, which in selected cases were isolated (5, 8). A C(4)- over C(2)-selectivity for ruthenium binding was established by protecting the C(2)-position with an iPr group on the imidazolium precursor, for which unique p-cymene (9) and cyclopentadienyl (10) Ru(II)-aNHC derivatives were synthesized. All complexes were applied in the transfer hydrogenation of ketones and in secondary alcohol oxidation, with higher catalytic activity for the p-cymene over the cyclopentadienyl systems, as well as the alkenyl- over the picolyl-containing aNHC complexes.
Malan, Frederick P.,Singleton, Eric,Van Rooyen, Petrus H.,Albrecht, Martin,Landman, Marilé
supporting information
p. 2624 - 2635
(2019/07/03)

Heterogeneously Catalysed Oxidative Dehydrogenation of Menthol in a Fixed-Bed Reactor in the Gas Phase
For the first time, the oxidative dehydrogenation of (?)-menthol to (?)-menthone and (+)-isomenthone in a marketable quality was carried out in a continuous gas phase reactor as a sustainable process using molecular oxygen as green oxidant and solid catalysts which do not contaminate the product mixture and which are easily to remove. The diastereomeric purity remained largely unchanged. Three types of catalysts were found to be very active and selective in the formation of menthone and isomenthone: AgSr/SiO2, CuO distributed on a basic support and RuMnCe/CeO2, where Ru, Mn and Ce exist in an oxidized state. The best overall yield of menthon/isomenthone obtained with an Ag-based catalyst was 58 % at 64 % selectivity, with a Cu-based catalyst 41 % at 51 % selectivity and with a Ru-based catalyst 68 % at 73 % selectivity. Reaction conditions were widely optimized.
Kulik, Anna,Neubauer, Katja,Eckelt, Reinhard,Bartling, Stephan,Panten, Johannes,K?ckritz, Angela
p. 1066 - 1075
(2019/06/24)

Biomimetic Transformation of p-Menthene Glucosides into p-Cymenes and Carvotanacetone
A biomimetic transformation of p-menthene glucosides into aromatic monoterpenoids that alluded to mechanisms for essential oil metabolism, which lines up with the precepts of molecular economy, is described. Acid treatment of (-)-(3S,4S,6R)-3,6-dihydroxy-1-menthene 3-O-β-d-glucopyranoside (1) and (-)-(3S,4R,5R,6S)-3,5,6-trihydroxy-1-menthene 3-O-β-d-glucopyranoside (2), from Ageratina glabrata, yielded p-cymene (7) and carvacrol (9). The stable oxidized intermediates (+)-(3S,4S,6R)-3,6-dihydroxy-1-menthene (3), (+)-(1S,4S,6R)-1,6-dihydroxy-2-menthene (4), (+)-(1R,4S,6R)-1,6-dihydroxy-2-menthene (5), (+)-(4S,6R)-yabunikkeol (6), (+)-(4S)-carvotanacetone (8), (+)-(1S,4S,5R,6R)-1,5,6-trihydroxy-2-menthene (15), (+)-(1R,4S,5R,6R)-1,5,6-trihydroxy-2-menthene (16), and the new (+)-(4S,5R,6S)-1(7),2-menthadiene (17) permitted establishment of the reaction mechanisms. The reactivity of the hydroxy groups of 4 and 5, as well as those of 15 and 16, was compared by acetylation reactions and supported by DFT calculations, revealing diminished reactivity in 4 and 15 due to the cis configuration of their hydroxy groups at C-1 and C-6. In addition, p-cymene (7) was detected as one of the major constituents of the essential oil of A. glabrata, which matches well with the biomimetic study.
Pardo-Novoa, Julio C.,Arreaga-González, Héctor M.,Galván-Gómez, Sinuhé,Rodríguez-García, Gabriela,Del Río, Rosa E.,Cerda-García-Rojas, Carlos M.,Joseph-Nathan, Pedro,Gómez-Hurtado, Mario A.
p. 485 - 491
(2019/03/08)

CuCl2/[hmim]Br: A new recyclable catalytic system for aromatization of cyclic dienes
The combination of copper(II) chloride and 1-hexyl-3-methylimidazolium bromide ([hmim]Br) as a new recyclable catalytic system in the presence of TBHP for aromatization of cyclic dienes is disclosed. The system could furnish the corresponding aromatics in moderate to excellent yield. The competition between aromatization and oxidation of benzylic substrates were also studied. This developed catalytic system could be reused and recycled at least nine times without significant loss of the producitivity.
Taboonpong, Piyada,Chavasiri, Warinthorn
p. 9 - 12
(2017/10/17)

Stable Carbocation Generated via 2,5-Cyclohexadien-1-one Protonation
Protonation of a substituted cyclohexadien-1-one (1) leads to the generation of carbocation [3]+, capable of effecting hydride abstraction and oxidation reactions. The molecular structure of [3]+ shows it to be structurally similar to [(p-MeO-C6H4)Ph2C]+. The ability to easily access [3]+ from stable and available precursors, such as 1 and commercially available acids, may allow a wider application of the growing number of trityl-based reactions in organic syntheses.
Fraser, Craig,Young, Rowan D.
p. 505 - 509
(2018/02/19)

Photocatalytic Properties and Mechanistic Insights into Visible Light-Promoted Aerobic Oxidation of Sulfides to Sulfoxides via Tin Porphyrin-Based Porous Aromatic Frameworks
Using concepts of biomimetic catalysis, a kind of tin porphyrin-based porous aromatic framework (SnPor@ PAF) with broad and strong optical absorption in the visible light region was successfully synthesized and subsequently used in the aerobic oxidation of sulfides to sulfoxides under ambient conditions and visible light irradiation, in which exhibited enzyme-like features of high efficiency and high selectivity. More interestingly, heterogeneous SnPor@PAF was naturally regarded as an intriguing and versatile photosensitizer for photocatalytic transformation and could be reused several times because of its robust and rigid porphyrin framework. As expected, their π-conjugated structure characteristic in the molecular skeleton might facilitate the activation of molecular oxygen under mild reaction conditions and promoted the production of reactive oxygen species (singlet oxygen (1O2) and superoxide radical anion (O2.?)), which would involve energy transfer and/or electron transfer process. Experimental investigations including emission quenching experiment, oxygen-isotope labelling, typical inhibition experiments, classical fluorescence probe study, photo-oxidation of α-terpinene and in situ electron spin resonance, could provide a mechanistic insight into the photocatalytic reactions. (Figure presented.).
Jiang, Jun,Luo, Rongchang,Zhou, Xiantai,Chen, Yaju,Ji, Hongbing
supporting information
p. 4402 - 4411
(2018/10/15)

A Manganese Nanosheet: New Cluster Topology and Catalysis
While the coordination chemistry of monometallic complexes and the surface characteristics of larger metal particles are well understood, preparations of molecular metallic nanoclusters remain a great challenge. Discrete planar metal clusters constitute nanoscale snapshots of cluster growth but are especially rare owing to the strong preference for three-dimensional structures and rapid aggregation or decomposition. A simple ligand-exchange procedure has led to the formation of a novel heteroleptic Mn6 nanocluster that crystallized in an unprecedented flat-chair topology and exhibited unique magnetic and catalytic properties. Magnetic susceptibility studies documented strong electronic communication between the manganese ions. Reductive activation of the molecular Mn6 cluster enabled catalytic hydrogenations of alkenes, alkynes, and imines.
Chakraborty, Uttam,Reyes-Rodriguez, Efrain,Demeshko, Serhiy,Meyer, Franc,Jacobi von Wangelin, Axel
supporting information
p. 4970 - 4975
(2018/03/28)

Selective Production of Renewable para-Xylene by Tungsten Carbide Catalyzed Atom-Economic Cascade Reactions
Tungsten carbide was employed as the catalyst in an atom-economic and renewable synthesis of para-xylene with excellent selectivity and yield from 4-methyl-3-cyclohexene-1-carbonylaldehyde (4-MCHCA). This intermediate is the product of the Diels–Alder reaction between the two readily available bio-based building blocks acrolein and isoprene. Our results suggest that 4-MCHCA undergoes a novel dehydroaromatization–hydrodeoxygenation cascade process by intramolecular hydrogen transfer that does not involve an external hydrogen source, and that the hydrodeoxygenation occurs through the direct dissociation of the C=O bond on the W2C surface. Notably, this process is readily applicable to the synthesis of various (multi)methylated arenes from bio-based building blocks, thus potentially providing a petroleum-independent solution to valuable aromatic compounds.
Dai, Tao,Li, Changzhi,Li, Lin,Zhao, Zongbao Kent,Zhang, Bo,Cong, Yu,Wang, Aiqin
supporting information
p. 1808 - 1812
(2018/02/10)

Methyl Perillate as a Highly Functionalized Natural Starting Material for Terephthalic Acid
Renewable commodity chemicals can be generated from plant materials. Often abundant materials such as sugars are used for this purpose. However, these lack appropriate functionalities and, therefore, they require extensive chemical modifications before they can be used as commodity chemicals. The plant kingdom is capable of producing an almost endless variety of compounds, including compounds with highly appropriate functionalities, but these are often not available in high quantities. It has been demonstrated that it is possible to produce functionalized plant compounds on a large scale by fermentation in microorganisms. This opens up the potential to exploit plant compounds that are less abundant, but functionally resemble commodity chemicals more closely. To elaborate this concept, we demonstrate the suitability of a highly functionalized plant compound, methyl perillate, as a precursor for the commodity chemical terephthalic acid.
Jongedijk, Esmer,van der Klis, Frits,de Zwart, Rozemarijn,van Es, Daan S.,Beekwilder, Jules
p. 201 - 203
(2018/03/06)

High-Yield Synthesis of a Long-Sought, Labile Ru-NHC Complex and Its Application to the Concise Synthesis of Second-Generation Olefin Metathesis Catalysts
The controlled reaction of [RuCl2(p-cymene)]2 with H2IMes generates the previously challenging precatalyst and Ru synthon RuCl2(p-cymene)(H2IMes) (Ru-2) in 96% isolated yield. Critical to success is inhibiting premature p-cymene displacement. This is achieved by carrying out the synthesis at ambient temperatures, protected from light, and at sufficient dilutions (25 mM in THF) to enable stoichiometric control and inhibit bimolecular decomposition. The ease with which p-cymene loss can be deliberately induced, however, is key to the utility of Ru-2 in both catalysis and catalyst synthesis. The transformation of Ru-2 into two second-generation olefin metathesis catalysts is described. RuCl2(H2IMes)(=CH(o-C6H4-OiPr)) (HII) and RuCl2(H2IMes)(PPh3)(=CHPh) GII′ (a desirable, faster-initiating analogue of GII) are accessible in ca. 80% yield over two steps from commercially available [RuCl2(p-cymene)]2. Synthesis from RuCl2(PPh3)3, in comparison, requires three or four steps for HII or GII′, respectively, and proceeds in lower yields.
Day, Craig S.,Fogg, Deryn E.
p. 4551 - 4555
(2018/12/14)

Synthesis of Fencholenic Aldehyde from α-pinene Epoxide on Modified Clays
The conditions for isomerization of α-pinene epoxide (2,3-epoxypinane) on modified clays that gave comparatively high contents (33.0%) of fencholenic (iso-campholenic) aldehyde in the product mixture were determined. An effective method for isolating it w
Sidorenko, A. Yu.,Ignatovich, Zh. V.,Ermolinskaya,Kravtsova,Baranovskii,Koroleva,Agabekov
p. 893 - 897
(2018/09/27)

Cyclometallated ruthenium catalyst enables late-stage directed arylation of pharmaceuticals
Biaryls are ubiquitous core structures in drugs, agrochemicals and organic materials that have profoundly improved many aspects of our society. Although traditional cross-couplings have made practical the synthesis of many biaryls, C-H arylation represents a more attractive and cost-effective strategy for building these structural motifs. Furthermore, the ability to install biaryl units in complex molecules via late-stage C-H arylation would allow access to valuable structural diversity, novel chemical space and intellectual property in only one step. However, known C-H arylation protocols are not suitable for substrates decorated with polar and delicate functionalities, which are commonly found in molecules that possess biological activity. Here we introduce a class of ruthenium catalysts that display a unique efficacy towards late-stage arylation of heavily functionalized substrates. The design and development of this class of catalysts was enabled by a mechanistic breakthrough on the Ru(ii)-catalysed C-H arylation of N-chelating substrates with aryl (pseudo)halides, which has remained poorly understood for nearly two decades.
Simonetti, Marco,Cannas, Diego M.,Just-Baringo, Xavier,Vitorica-Yrezabal, I?igo J.,Larrosa, Igor
p. 724 - 731
(2018/06/29)

Reevaluation of the Palladium/Carbon-Catalyzed Decarbonylation of Aliphatic Aldehydes
An improved method for the decarbonylation of aliphatic aldehydes by using a commercially available Pd/C catalyst is described. The reaction conditions are suitable for linear, cyclic, or sterically demanding substrates, as they afford the corresponding alkanes in yields of up to 99%. In addition, this Pd/C-catalyzed method exhibits good functional-group tolerance. A comparison of previously reported methods with the present one showed that the reaction conditions play a crucial role in the outcome of the reaction. The method can also be applied in a two-step reaction sequence for the synthesis of industrially important compounds.
Ajda?i?, Vladimir,Nikoli?, Andrea,Kerner, Michael,Wipf, Peter,Opsenica, Igor M.
supporting information
p. 1781 - 1785
(2018/08/12)

A mechanistic study of transfer hydrogenation catalyzed by cyclometallated ruthenium half-sandwich complexes
Transfer hydrogenation of aromatic ketones catalyzed by eight cyclometallated ruthenium half-sandwich complexes, including three new complexes, was examined. The catalytic process was studied using different ratios of substrate to base and base to catalyst and using a deuterated reductant. Optimum conditions for catalysis were shown to be in the presence of higher amounts of base in refluxing isopropanol. Under these conditions, the complexes were reduced in situ to give Ru(0) nanoparticles invisible to the naked eye. The nanoparticles were characterized by TEM, DLS and XPS. The catalytic transfer hydrogenation, under conditions in which nanoparticles were generated, was found to be far greater than the transfer hydrogenation by the molecular catalyst. Complete characterization of the three new complexes, including the X-ray crystallographic characterization of these complexes was carried out.
Din Reshi, Noor U.,Senthurpandi, Dineshchakravarthy,Samuelson, Ashoka G.
p. 189 - 199
(2018/05/04)

Selective endoperoxide formation by heterogeneous TiO2 photocatalysis with dioxygen
We report the selective formation of endoperoxides by aerobic TiO2 photocatalysis through the cyclic addition of dioxygen and a non-conjugated diene, the first heterogeneous catalytic system for endoperoxide synthesis. This green protocol does not require any additive and the photocatalyst is abundant and recyclable, providing a yield up to 64% and >20:1 diastereoselectivity. Mechanistic investigations were carried out by using product analysis, kinetic studies, O-18 labelling experiments, electron-spin resonance and a set of quenching experiments. Superoxide (but not singlet oxygen, triplet oxygen or peroxide) is directly involved in the reaction cascade to form the endoperoxide product. The new findings may be helpful for future for designing eco-friendly and energy sustainable strategies for selective oxygenation reactions using semiconductors, O2 and sunlight.
Qiao, Xiaofeng,Biswas, Subharanjan,Wu, Wenli,Zhu, Feng,Tung, Chen-Ho,Wang, Yifeng
supporting information
p. 2421 - 2427
(2018/04/11)

Synthesis of Highly Substituted Arenes via Cyclohexadiene-Alkene C-H Cross Coupling and Aromatization
The development of a cross-coupling method for the regioselective β-alkenylation of 2,5-cyclohexadiene carboxylic acid derivatives to form ortho-alkenylarenes through in situ decarboxylation and aromatization is described. The carboxylic acid functionality is used as a traceless directing group for efficient and mild β-alkenylation. The modular sequence comprises a reductive Birch α-alkylation, ionic ?-alkylation followed by a Pd-catalyzed decarboxylative β-alkenylation with subsequent aromatization resulting in an overall three-fold ipso-para-ortho functionalization of readily accessed benzoic acid derivatives. Efficient synthesis of various alkyl-alkenylarenes under mild conditions in moderate to excellent yields is presented.
Bhunia, Anup,Studer, Armido
p. 1213 - 1217
(2018/02/14)

Fluoropolymer-Coated PDMS Microfluidic Devices for Application in Organic Synthesis
In recent years there has been huge interest in the development of microfluidic reactors for the synthesis of small molecules and nanomaterials. Such reaction platforms represent a powerful and versatile alternative to traditional formats since they allow for the precise, controlled, and flexible management of reactive processes. To date, the majority of microfluidic reactors used in small-molecule synthesis have been manufactured using conventional lithographic techniques from materials such as glasses, ceramics, stainless steel, and silicon. Surprisingly, the fabrication of microfluidic devices from such rigid materials remains ill-defined, complex, and expensive. Accordingly, the microfluidic toolkit for chemical synthesis would significantly benefit from the development of solvent-resistant microfluidic devices that can be manufactured using soft-lithographic prototyping methods. Whilst significant advances in the development of solvent-resistant polymers have been made, only modest steps have been taken towards simplifying their use as microfluidic reactors. Herein, we emphasize the benefits of using a commercially available, amorphous perfluorinated polymer, CYTOP, as a coating with which to transform PDMS into a chemically inert material for use in organic synthesis applications. Its efficacy is demonstrated through the subsequent performance of photooxidation reactions and reactions under extremely acidic or basic conditions.
Yang, Tianjin,Choo, Jaebum,Stavrakis, Stavros,de Mello, Andrew
p. 12078 - 12083
(2018/08/21)

A comparative study of catalytic performance of rare earth metal-modified beta zeolites for synthesis of cymene
A series of zeolite (LaB, CeB, and PrB) containing rare earth metals lanthanum (La), cerium (Ce), and praseodymium (Pr) were used for transalkylation reaction. The modified beta zeolites were characterized by EDS, XRD, BET, FTIR, and TPD. The surface area and acidities of the zeolite samples modified with various rare earth metals are considerably different. The effect of various process parameters like metal loading (2-10 wt%), catalyst loading (1.44-8.63 w/w%), temperature (448-573 K), reactant ratio 1-15, and space time (3.2-9.29 kg h/kmol) on the conversion of reactant and selectivity of product was studied. Catalytic performance of praseodymium-modified beta zeolite shows highest cumene conversion (86.4 wt%) and cymene selectivity (65.7 wt%) compared to other zeolites. The maximum cumene conversion and cymene selectivity were obtained at 523 K, toluene-to-cumene ratio of 9:1, and a space time of 9.29 kg h/kmol. Kinetic modeling of the reaction was done to estimate the reaction kinetic constants and adsorption constants. The activation energy of the transalkylation was found to be 61.44 kJ/mol.
Thakur, Ruchika,Gupta, Raj K.,Barman, Sanghamitra
p. 137 - 148
(2017/02/05)

Solvent-free isomerization of 3-carene to 2-carene using Na/o-chlorotoluene catalyst in trans-isolimonene production
Trans-isolimonene is one of the important compound in drugs development. This compound can be made by isomerization of inexpensive 3-carene via 2-carene using Na/o-chlorotoluene catalyst in xylene. The existence of xylene as a solvent requires a further separation process that can reduce the efficiency when applied in the bulk industry. The isomerization of 3-carene to 2-carene has been studied in solvent free reaction compared by isomerization without xylene solvent. The result showed that the isomerization can also occur in solvent-free condition. Solventfree isomerization gave 27.72% of conversion and 83.27% of selectivity while isomerization with solvent gave 23.59% of conversion and 86.87% of selectivity.
Julianto, Tatang Shabur,Jumina,Jojo, Hardjono Sastrohamid,Mustofa
p. 3107 - 3111
(2018/01/17)

Ruthenium arene complexes with triphenylphosphane ligands: Cytotoxicity towards pancreatic cancer cells, interaction with model proteins, and effect of ethacrynic acid substitution
The ruthenium-arene complexes [(η6-p-cymene)RuCl2(κP-PPh2(4-C6H4CO2H))], 1, [(η6-p-cymene)RuCl(κ2P,O-PPh2(2-C6H4CO2))], 2, [(η6-p-cymene)RuCl2(κP-PPh2(2-C6H4OCO-EA))], 3, and [(η6-p-cymene)RuCl2(κP-PPh2(4-C6H4CO2CH2CH2OCO-EA))], 4 (EA-CO2H = ethacrynic acid), were synthesized in good to high yields and characterized by analytical techniques, IR, UV-Vis and multinuclear NMR spectroscopy, and single crystal X-ray diffraction in the cases of 1 and 2. The unstable compounds [(η6-arene)RuCl2(κP-PPh2(2-C6H4CO2CH2CH2OCO-EA))] (arene = p-cymene, 5a; arene = C6H6, 5b) were obtained and identified in solution by NMR. Electrochemical and spectro-electrochemical experiments were performed in order to assess the redox behaviour of 1-4 in CH2Cl2. The in vitro cytotoxicity of 1-4 was determined on the human pancreatic cancer cell line BxPC3 and the mouse embryo fibroblast Balb/3T3 Clone A31 cell line, the latter acting as a model for normal cells. Furthermore, the interaction of 1, 3 and 4 with two model proteins was investigated by high resolution ESI-MS.
Biancalana, Lorenzo,Pratesi, Alessandro,Chiellini, Federica,Zacchini, Stefano,Funaioli, Tiziana,Gabbiani, Chiara,Marchetti, Fabio
supporting information
p. 14574 - 14588
(2017/11/28)

A general strategy to add diversity to ruthenium arene complexes with bioactive organic compounds: Via a coordinated (4-hydroxyphenyl)diphenylphosphine ligand
Esterification of (4-hydroxyphenyl)diphenylphosphine, coordinated to the [Ru(η6-p-cymene)Cl2] fragment, allows a series of bioactive carboxylic acids to be introduced directly into the organometallic molecule. Evaluation of the compounds on human ovarian cancer cells reveals synergistic enhancements in their antiproliferative activity relative to their bioactive organic and organometallic precursors.
Biancalana, Lorenzo,Batchelor, Lucinda K.,De Palo, Alice,Zacchini, Stefano,Pampaloni, Guido,Dyson, Paul J.,Marchetti, Fabio
supporting information
p. 12001 - 12004
(2017/09/25)

Iron-Catalyzed Isopropylation of Electron-Deficient Aryl and Heteroaryl Chlorides
Traditional methods for the preparation of secondary alkyl-substituted aryl and heteroaryl chlorides challenge both selectivity and functional group tolerance. This contribution describes the use of statistical design of experiments to develop an effective procedure for the preparation of isopropyl-substituted (hetero)arenes with minimal isopropyl to n-propyl isomerization. The reaction tolerates electronically diverse aryl chloride coupling partners, with excellent conversion observed for strongly electron-deficient aromatic rings, such as esters and amides. Electron-rich systems, including methyl- and methoxy-substituted aryl chlorides, were found to be less reactive. Furthermore, the reaction was found to be most successful when heteroaryl chlorides were submitted to the cross-coupling protocol. By mapping substituent effects on reaction selectivity, we were able to show that electron-deficient aryl chlorides are essential for efficient coupling, and use electronic structure calculations to predict the likelihood of successful coupling through the estimation of the electron affinity of each aryl chloride. Moderate isolated yields were achieved with selected aryl chlorides, and moderate to good isolated yields were obtained for all the heteroaryl chlorides coupled. Excellent selectivity was observed when a 2,6-dichloroquinoline was used, allowing mono-substitution on a challenging substrate. (Figure presented.).
Sanderson, James N.,Dominey, Andrew P.,Percy, Jonathan M.
p. 1007 - 1017
(2017/03/27)

Singlet oxygen generation from poly[4-diacetoxyiodo]styrene and hydrogen peroxide
Treatment of hydrogen peroxide with a polymer-supported hypervalent iodine compound, poly[4-diacetoxyiodo] styrene (PDAIS), generates singlet molecular oxygen (1O2). Singlet oxygen generation was proved by trapping with typical organic compounds such as conjugated dienes, aromatic dienes, and electron-rich alkene. When compared to monomer analogue, the use of PDAIS in peroxidation of substrates gave slightly better yields (45%–96%). Regeneration and reuse of PDAIS showed similar activity. The mechanism underlying generation of singlet oxygen and reaction scope was examined.
?atir, Mustafa
p. 467 - 475
(2017/09/15)

Continuous Photo-Oxidation in a Vortex Reactor: Efficient Operations Using Air Drawn from the Laboratory
We report the construction and use of a vortex reactor which uses a rapidly rotating cylinder to generate Taylor vortices for continuous flow thermal and photochemical reactions. The reactor is designed to operate under conditions required for vortex generation. The flow pattern of the vortices has been represented using computational fluid dynamics, and the presence of the vortices can be easily visualized by observing streams of bubbles within the reactor. This approach presents certain advantages for reactions with added gases. For reactions with oxygen, the reactor offers an alternative to traditional setups as it efficiently draws in air from the lab without the need specifically to pressurize with oxygen. The rapid mixing generated by the vortices enables rapid mass transfer between the gas and the liquid phases allowing for a high efficiency dissolution of gases. The reactor has been applied to several photochemical reactions involving singlet oxygen (1O2) including the photo-oxidations of α-terpinene and furfuryl alcohol and the photodeborylation of phenyl boronic acid. The rotation speed of the cylinder proved to be key for reaction efficiency, and in the operation we found that the uptake of air was highest at 4000 rpm. The reactor has also been successfully applied to the synthesis of artemisinin, a potent antimalarial compound; and this three-step synthesis involving a Schenk-ene reaction with 1O2, Hock cleavage with H+, and an oxidative cyclization cascade with triplet oxygen (3O2), from dihydroartemisinic acid was carried out as a single process in the vortex reactor.
Lee, Darren S.,Amara, Zacharias,Clark, Charlotte A.,Xu, Zeyuan,Kakimpa, Bruce,Morvan, Herve P.,Pickering, Stephen J.,Poliakoff, Martyn,George, Michael W.
supporting information
p. 1042 - 1050
(2017/07/26)

Direct conversion of carboxylic acids (Cn) to alkenes (C2n - 1) over titanium oxide in absence of noble metals
Carbon-carbon bond formations and deoxygenation reactions are important for biomass up-grading. The classical ketonic decarboxylation of carboxylic acids provides symmetrical ketones with 2n + 1 carbon atoms and eliminates three oxygen atoms. Herein, this reaction is carried out with titanium oxide at 400°C, and an olefin with 2n + 1 carbon atoms is obtained instead of the ketone. For olefin formation hydrogen transfer reactions are required from suitable precursors to form aromatics and coke. Additional aldol condensation reactions increase further molecular weight in the product mixture. Hence, a combination of titanium oxide with a hydrodeoxygenation bed provides double amount of diesel fuel as the combination with zirconium oxide when reacting hexose-derived pentanoic acid.
Oliver-Tomas, Borja,Renz, Michael,Corma, Avelino
p. 1 - 8
(2016/02/05)

Hybrid catalysts based on platinum and palladium nanoparticles for the hydrogenation of terpenes under slurry conditions
Catalysts based on platinum and palladium nanoparticles immobilized in mesoporous phenolformaldehyde polymers modified with sulfo groups have been used for the hydrogenation of a number of terpenes, such as (S)-(–)-limonene, α-terpinene, γ-terpinene, and terpinolene. It has been found that Pd-containing catalysts exhibit higher activity in the exhaustive hydrogenation of terpenes, whereas Pt-containing catalysts have high selectivity for p-menthene.
Karakhanov,Boronoev,Subbotina,Zolotukhina,Maximov,Filippova, T. Yu.
p. 1114 - 1122
(2017/02/15)

Mechanisms into dehydroaromatization of bio-derived limonene to: P -cymene over Pd/HZSM-5 in the presence and absence of H2
The mechanisms of dehydroaromatization of limonene to p-cymene are intrinsically investigated over Pd/HZSM-5 under different N2/H2 atmospheres using the mathematical tool of Matlab. It is found that the dehydroaromatization reaction network starts with the isomerization step, and is followed by the sequential dehydrogenation in the presence of N2 or H2 at the selected system. The addition of hydrogen in the atmosphere would not change this reaction pathway, but leads to lower selectivity of p-cymene due to the accelerated hydrogenation rates on the double bonds. Besides, the additional hydrogen speeds up the overall reaction by facilitating the isomerization step on limonene while impeding its reverse reaction, as isomerization of limonene is proved to be the determining step of the whole dehydroaromatization reaction. Furthermore, the presence of hydrogen dramatically decreases the apparent and true activity energy of the target dehydroaromatization reaction and reduces the impact of temperatures to such processes compared to that with a N2 gas carrier.
Cui, Huimei,Zhang, Jingjing,Luo, Zhicheng,Zhao, Chen
p. 66695 - 66704
(2016/08/02)

Iodine, a Mild Reagent for the Aromatization of Terpenoids
Efficient procedures based on the use of iodine for the aromatization of a series of terpenoids possessing diene and homoallylic or allylic alcohol functionalities are described. Different examples are reported as a proof-of-concept study. Furthermore, iodine also proved to mediate the dehydrogenation of testosterone.
Domingo, Victoriano,Prieto, Consuelo,Silva, Lucia,Rodilla, Jess M. L.,Qulez Del Moral, Jos F.,Barrero, Alejandro F.
supporting information
p. 831 - 837
(2016/05/24)