- The effect of catalyst preparation conditions on the synthesis of menthol from citronellal on Ru/H-BEA
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Heterogeneous Ru/H-BEA catalysts are suitable catalysts for the one-pot transformation of citronellal to menthols, which requires a combined cyclization-hydrogenation step. Here, we report the role of different preparation conditions-namely the choice of the Ru-precursor (Ru(NO)(NO3)3), Ru(acac)3, RuCl3 and Ru3(CO)12) as well as the reduction temperature (523-923 K) of the catalyst. Using Ru(NO)(NO3)3 as precursor the highest activity was obtained, while the product distribution was not strongly affected by the choice of the precursor. On the contrary the reduction temperature leads to very different product distributions: Increasing it from 623 K to 923 K for a 1%Ru/H-BEA-25 catalyst the competitive hydrogenation of citronellal was diminished, which leads to an increased selectivity to menthols from 77% to 87% and additional the activity increases with a factor of 3.4. This behaviour might be due to a dealumination of the zeolite during reduction at higher temperatures. Moreover, in combination with appropriate reaction conditions a yield to menthols of 92% can be reached.
- Pl??er, Jutta,Dedeaga, Fatma,Lucas, Martin,Claus, Peter
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- Development of microchannel reactors using polysilane-supported palladium catalytic systems in capillaries
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A new method of immobilizing Pd catalysts on the channel wall of a capillary by using polysilane with metal oxide has been developed, and applied to hydrogenation reactions. The Royal Society of Chemistry.
- Ueno, Masaharu,Suzuki, Toshie,Naito, Takeshi,Oyamada, Hidekazu,Kobayashi, Shu
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- SYNTHESIS OF ETHYL 3,7,11-TRIMETHYL-2,4-DODECADIENOATE (HYDROPRENE) FROM 4-METHYLTETRAHYDROPYRAN
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A new pathway has been proposed for the synthesis of the ethyl ester of 3,7,11-trimethyl-2,4-dodecadienoate (juvenoid hydroprene) from available 4-methyltetrahydropyran.The cleavage of the latter to 3-methyl-5-bromo-1-acetoxypentane and coupling with isobutylmagnesium bromide gave tetrahydrogeraniol, which was oxidized to the corresponding aldehyde.The reaction of this aldehyde with allylmagnesium chloride and subsequent oxidation by O2/PdCl2-CuCl led to 6,10-dimethyl-3E-undecen-2-one, which was converted by a known method to the desired product as a mixture of 70 percent 2E,4E- and 30 percent 2Z,4E-stereoisomers.The yield of hydroprene in the six-step synthesis was 32 percent relative to 4-methyltetrahydropyran.
- Odinokov, V. N.,Ishmuratov, G. Yu.,Kharisov, R. Ya.,Lomakina, S. I.,Tolstikov, G. A.
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- New Route to Stabilize Ruthenium Nanoparticles with Non-Isolable Chiral N-Heterocyclic Carbenes
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Ru nanoparticles (RuNPs) stabilized by non-isolable chiral N-heterocyclic carbenes (NHCs), namely SIDPhNp ((4S,5S)-1,3-di(naphthalen-1-yl)-4,5-diphenylimidazolidine) and SIPhOH ((S)-3-((1S,2R)-2-hydroxy-1,2-diphenylethyl)-1-((R)-2-hydroxy-1,2-diphenylethyl)-4,5-dihydro-3H-imidazoline), have been synthesized through a new procedure that does not require isolation of the free carbenes. The obtained RuNPs have been characterized by state-of-the-art techniques and their surface chemistry has been investigated by FTIR and solid-state MAS NMR upon the coordination of CO, which indicated the presence of free and reactive Ru sites. Their catalytic activity has been tested in various hydrogenation reactions involving competition between different sites, whereby interesting differences in selectivity were observed, but no enantioselectivity.
- Martnez-Prieto, Luis Miguel,Ferry, Anglique,Lara, Patricia,Richter, Christian,Philippot, Karine,Glorius, Frank,Chaudret, Bruno
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- Transfer hydrogenation of citral to citronellol with Ru complexes in the mixed solvent of water and polyethylene glycol
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The transfer hydrogenation of citral to citronellol was studied with [RuCl2(benzene)]2 catalyst in a mixed solvent of water and polyethylene glycol (H2O-PEG). The influence of several important factors including hydrogen source, solvent, temperature and active species is discussed. Under the present conditions, citronellol was produced with an extremely high selectivity above 90%. The Ru complexes could be immobilized in the H2O-PEG phase well and separated from organic products successfully. Moreover, a stable catalytic activity was obtained after the first run, although the decomposition of Ru complexes occurred during the recycling processes. The selectivity to citronellol decreased but kept a stable level about 60% in the recycling runs. Copyright
- Cheng, Haiyang,Liu, Ruixia,Hao, Jianmin,Wang, Qiang,Yu, Yancun,Cai, Shuxia,Zhao, Fengyu
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- Colloidal noble-metal and bimetallic alloy nanocrystals: A general synthetic method and their catalytic hydrogenation properties
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A general single-step strategy has been developed for the direct thermal decomposition of noble-metal salts in octadecylamine to synthesize octahedron- and rod-shaped noblemetal aggregates and monodisperse noble-metal or bimetallic alloy nanocrystals without introducing any additive into the system. It has presented a facile and economic way to fabricate these nanocrystals, especially alloy nanocrystals, which does not require a post-synthesis solid-state annealing process. The morphology of the nanocrystals can be easily controlled by tuning the synthetic temperature. Their ability to catalyze heterogeneous Suzuki coupling reactions has been investigated and showed satisfactory catalytic activity. The catalytic performanee of the monometallic and bimetallic alloy nanocrystals were also evaluated in the selective hydrogenation of citral in a conventional organic solvent (toluene) and a green solvent (supercritical carbon dioxide, scCO2). Interestingly, the catalysts performed differently to each other when they were in ScCO2 owing to the different morphology, which should be readily optimized for further use.
- Song, Shuyan,Liu, Ruixia,Zhang, Yu,Feng, Jing,Liu, Dapeng,Xing, Yan,Zhao, Fengyu,Zhang, Hongjie
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- Selective hydrogenation of citral over a carbon-titania composite supported palladium catalyst
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A novel carbon-titania composite material, C/TiO2, has been prepared by growing carbon nanofibers (CNFs) on TiO2 surface via methane decomposition using Ni-Cu as a catalyst. The C/TiO2 was used for preparing supported palladium catalyst, Pd/C/TiO2. The support and Pd/C/TiO2 catalyst were characterized by BET, SEM, XRD and TG-DTG. Its catalytic performance was evaluated in selective hydrogenation of citral to citronellal, and compared with that of activated carbon supported Pd catalyst. It was found that the Pd/C/TiO2 catalyst contains 97% of mesopores. And it exhibited 88% of selectivity to citronellal at citral conversion of 90% in citral hydrogenation, which was much higher than that of activated carbon supported Pd catalyst. This result may be attributed to elimination of internal diffusion limitations, which were significant in activated carbon supported Pd catalyst, due to its microporous structure. A novel palladium catalyst supported on carbon-titanium composite, Pd/C/TiO 2, has been prepared via chemical reduction process. It contains 97% mesopores and exhibited higher selectivity to citronellal in citral hydrogenation compared to formed activated carbon supported palladium catalyst, which was attributed to elimination of internal diffusion limitations.
- Zhu, Jie,Lu, Mohong,Li, Mingshi,Zhu, Jianjun,Shan, Yuhua
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- Alkaline modifiers as performance boosters in citral hydrogenation over supported ionic liquid catalysts (SILCAs)
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Supported ionic liquid catalysts (SILCAs) consist of nano-scale catalytic species immobilized in an ionic liquid layer which, in turn, is immobilized on a solid support. In this work, novel SILCAs containing various inorganic alkaline modifiers (e.g. potassium hydroxide) were prepared and applied in citral hydrogenation reactions. The supported ionic liquid catalyst systems demonstrated enhanced reaction rates and improved selectivities toward citronellal in citral hydrogenation. With the addition of an alkaline modifier into ionic liquid layer, the catalyst selectivity increased from 16% to 74%. In fact, a highly selective reaction route toward citronellal was accomplished.
- Salminen, Eero,Virtanen, Pasi,Kordás, Krisztián,Mikkola, Jyri-Pekka
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- New terpene hydrocarbons from the alligatoridae (crocodylia, reptilia)
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The contents of the paracloacal gland secretions of the alligatorids Alligator mississippiensis, A. sinensis, Paleosuchus palpebrosus, and P. trigonatus were investigated. Novel acyclic hydrocarbon terpenes with a rare trisubstituted 2,4-diene system were identified in the secretions of A. sinensis, P. palpebrosus, and P. trigonatus. The structures of the monoterpene (2E,4E)-3,7-dimethyl-2,4-octadiene (9) and the sesquiterpene (2E,4E,7S)-3,7,11-trimethyl-2,4-dodecadiene (14) were proven by synthesis and gas chromatography on a chiral phase. Several other new terpenes (11, 16, 17, 18, 19, and 20) related to these components also were present in the secretions, as well as the known compounds myrcene (6), (E)-β-farnesene (4), (E)-β-springene (3), squalene (5), cembrene A (1), and 11,12-dihydrocembren-10-one (2).
- Schulz, Stefan,Krueckert, Karsten,Weldon, Paul J.
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- Catalytic performance in selective hydrogenation of citral of bimetallic Pt-Sn catalysts supported on MgAl2O4 and γ-Al 2O3
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The liquid phase citral hydrogenation, using Pt and PtSn catalysts supported on MgAl2O4 and γ-Al2O 3, was studied in a stirred reactor at 70 °C and atmospheric pressure. It was found that the addition of Sn to the Pt catalysts increases the selectivity to double unsaturated alcohols for both catalyst series. Besides, monometallic catalysts hydrogenate the α,β-unsaturation with a high selectivity in absence of cyclization secondary products. The performance of these catalysts in the citral hydrogenation was related with the characteristics of the metallic phase. Results from test reactions - cyclohexane dehydrogenation (CHD) and cyclopentane hydrogenolysis (CPH) - H2 chemisorption, 2-propanol dehydration, temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS), were used to explain the influence of the support and the Sn loading and postulate the models of the catalytic metallic surface. Results indicated that, a fraction of ionic Sn would be deposited near Pt, thus increasing the polarization of the carbonyl group, and a fraction of metallic Sn could form Pt-Sn alloy phases that would hinder the hydrogenation of the olefinic bonds and would be active to the hydrogenation of the carbonyl group. Both effects contribute to a higher selectivity to unsaturated alcohols in bimetallic PtSn/Al2O3 catalysts than PtSn/MgAl2O4 ones, which display a low alloy formation.
- Zgolicz, Patricia D.,Rodríguez, Virginia I.,Vilella, Irene M.J.,De Miguel, Sergio R.,Scelza, Osvaldo A.
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- Selective catalytic activity of ball-shaped Pd@MCM-48 nanocatalysts
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Remarkable selectivity is achieved in the cleavage of benzyl ethers using ball-shaped palladium nanocatalysts, Pd@MCM-48, in an MCM-48 matrix. The unique nanocatalysts not only feature unprecedented complete hydrogenolysis selectivity of a benzyl ether over hydrogenation of a double bond, but also demonstrate selective cleavage of unsubstituted benzyl ether over substituted benzyl ethers. The Royal Society of Chemistry 2006.
- Lee, Hee-Yoon,Ryu, Suyoung,Kang, Hongkyu,Jun, Young-Wook,Cheon, Jinwoo
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- Synthesis of S-(+)-hydroprene
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A novel path to S-(+)-hydroprene (1) starting from the technical grade S-(+)-dihydromyrcene (2, e.e. > 50percent) is proposed.The latter was selectively transformed into S-3,7-dimethyloctanal (5) in three steps including hydroalumination.The reactions of 5 with allyl- or methallylmagnesium chloride followed, respectively, either by oxygenation in the presence of PdCl2/CuCl or by ozonolysis, afford S,E-6,10-dimethyl-3-undecen-2-one (7) which was treated with ethoxyethynylmagnesium bromide to give the title juvenile hormone analogue in ca. 23percent overall yield.
- Odinokov, V. N.,Ishmuratov, G. Yu.,Kharisov, R. Ya.,Serebryakov, E. P.,Tolstikov, G. A.
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- Liquid-phase hydrogenation of citral over Pt/SiO2 catalysts - II. Hydrogenation of reaction intermediate compounds
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Liquid-phase hydrogenation of the four principal reaction intermediates during citral hydrogenation (nerol, geraniol, citronellal, and citronellol) was studied at 298 and 373 K under 20 atm H2 at concentrations of 0.5-1M in hexane. Decomposition of geraniol and nerol to form adsorbed CO on Pt as an inhibitor was proposed to be responsible for the activity minimum observed during citral hydrogenation. A decrease in the initial reaction rate as temperature increased from 298 to 373 K was exhibited during the hydrogenation of all four compounds. Furthermore, simultaneous hydrogenation of citronellal and geraniol at 298 K resulted in a continuous decrease in the rate of citronellal disappearance in contrast to the nearly constant rate of disappearance observed during hydrogenation of citronellal alone. Competitive hydrogenation of citral with either geraniol or citronellal showed that geraniol hydrogenation to citronellol was kinetically insignificant during citral hydrogenation at 373 K. The relative rates of hydrogenation of the compounds indicated that the hydrogenation rate of the C=C bond in this family of compounds was greater than that of the C=O bond, as evidenced by the ordering of the hydrogenation activity: geraniol > nerol > citronellol > E-citral > citronellal _ Z-citral. The product distributions obtained during hydrogenation of citronellal indicated that higher reaction temperatures favor activation of the C=O bond relative to the C=C bond.
- Vannice,Singh,Sysak
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- Modular Bidentate Hybrid NHC-Thioether Ligands for the Stabilization of Palladium Nanoparticles in Various Solvents
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The synthesis of four different bidentate hybrid NHC-thioether ligands is presented. The corresponding palladium nanoparticles are stable in various solvents, depending on the ligand used, and show high chemoselectivity in the hydrogenation of olefins. The solubility of the nanoparticles can be switched multiple times depending on the pH value of the solvent. XPS analysis (which shows a subtle shift in the binding energy) was identified as a convenient tool to establish the binding mode of NHC ligands.
- Rühling, Andreas,Schaepe, Kira,Rakers, Lena,Vonh?ren, Benjamin,Tegeder, Patricia,Ravoo, Bart Jan,Glorius, Frank
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- A novel type of Pd/C-catalyzed hydrogenation using a catalyst poison: Chemoselective inhibition of the hydrogenolysis for O-benzyl protective group by the addition of a nitrogen-containing base
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A mild and chemoselective hydrogenation method for a variety of reducible functional groups distinguishing front aliphatic and aromatic' benzyl ethers was accomplished by the addition of an appropriate nitrogen- containing base to the Pd/C-catalyzed hydrogenation system.
- Sajiki, Hironao,Hirota, Kosaku
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- Alkylglucosides with isoprenoid-type hydrophobic chains-effects of hydrophobic chain size on the aqueous phase behavior
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Aqueous phase diagrams were constructed for two new alkylglucosides with isoprenoid-type hydrophobic chains, viz. 1-O-β-(3,7-dimethyloctyl)-D- glucopyranoside, β-Glc(Ger), and 1-O-β-(3,7,11,15- tetramethylhexadecyl)-D-glucopyranoside, β-Glc(Phyt). In a low concentration regime, from 0.17 to 34wt.% β-Glc(Ger), the β-Glc(Ger)/water system exhibits two phase, a dilute (L1 dil) and a concentrated isotropic phase (L1 conc), coexistence region. Above about 62wt.% β-Glc(Ger), an Lα phase is formed. The extent of the L1dil+L 1conc two-phase region decreases as temperature increases and totally disappears above 130°C, exhibiting an upper critical temperature. The β-Glc(Phyt)/water system exhibits an Lα phase above 78wt.% surfactant below which, an Lα + water two-phase region appears. One notable feature of these compounds is their low values of Krafft-eutectic temperature, TK, e.g. the value of TK for β-Glc(Phyt) is below 0°C although the total number of carbon atoms in the hydrophobic chain is as large as 20.
- Salkar, Rajesh A.,Minamikawa, Hiroyuki,Hato, Masakatsu
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- Continuous flow synthesis of menthol: Via tandem cyclisation-hydrogenation of citronellal catalysed by scrap catalytic converters
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A continuous flow synthesis of menthol starting from citronellal catalysed by scrap catalytic converters is reported. The reaction was conducted in a tandem system connecting in series two catalytic systems, with the first having Lewis acid properties (favouring the cyclisation of citronellal to isopulegols) and the second having hydrogenation catalytic activity (catalysing the hydrogenation of isopulegols to menthols). A Lewis acid catalyst was prepared by supporting iron oxide nanoparticles over a waste material, i.e. the ceramic core of scrap catalytic converters (SCATs) via a microwave assisted method. Most importantly, SCATs, containing a low residual noble metal content, could be directly employed in the second step as hydrogenation catalysts. The reaction was performed studying the influence on the yield and selectivity to (-)-menthol of various reaction parameters (T, p and flow rate). Under the best reaction conditions (at a flow rate of 0.1 mL min-1 and at 373 K and 413 K for cyclisation and hydrogenation steps respectively) a conversion of >99% of (+)-citronellal to (-)-menthol with 77% final yield was achieved.
- Zuliani, Alessio,Cova, Camilla Maria,Manno, Roberta,Sebastian, Victor,Romero, Antonio A.,Luque, Rafael
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- Universal approach to the synthesis of juvenoid hydroprene and methoprene from 4-methyltetrahydropyran
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A universal approach to the synthesis of juvenoid hydroprene and methoprene was developed on the basis of monoalkylation of acetoacetate by 1-acetoxy-5-bromo-3-methylpentane, the product of acidic decyclization of 4-methyltetrahydropyran.
- Ishmuratov,Yakovleva,Galyautdinova,Faifer,Kharisov,Zorin,Tolstikov
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- Selective hydrogenation of citral by noble metals supported on carbon xerogels: Catalytic performance and stability
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A series of monometallic Pt, Ir and Ru-catalysts deposited on carbon xerogel microspheres was prepared, exhaustively characterized and used in the selective hydrogenation of citral. A similar metal particle size is obtained in all cases after He-pretreatment, allowing the comparison between metals; the catalytic activity increases in the sense Ir 2-flow leading to an important loss of activity, especially for Ru-catalysts. Pt and Ir-catalysts are more selective than Ru-catalysts, reaching selectivity values to unsaturated alcohols of around 80%. Thus, in terms of yields to these valuable products Pt-catalysts seem to be the most appropriate active phase. Nevertheless, reutilization experiments showed that Ir-catalyst maintained a good performance while a severe deactivation is observed for Pt-catalysts. This fact is discussed on the basis of the different nature of the deposits formed during reaction.
- Bailón-García, Esther,Carrasco-Marín, Francisco,Pérez-Cadenas, Agustín F.,Maldonado-Hódar, Francisco J.
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- Simple H2-free hydrogenation of unsaturated monoterpenoids catalyzed by Raney nickel
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A series of monoterpenoids (citral, carvone, menthone, camphor) as well as cyclohexanone and hex-5-en-2-one were subjected to transfer hydrogenation with PriOH/Raney nickel system at 82 or 150 °C. Among monoterpenoids, citral and carvone underwent full conversion at 82 °C within 5 h.
- Philippov, Alexey A.,Chibiryaev, Andrey M.,Martyanov, Oleg N.
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- Synthesis of Co-Sn intermetallic nanocatalysts toward selective hydrogenation of citral
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In this work, three supported Co-Sn intermetallic compound (IMC) catalysts (Co2.9Sn2, CoSn and CoSn2) with a particle size of ～20 nm were prepared via a facile hydrotalcite approach, and their catalytic performances were evaluated in the selective hydrogenation of citral to unsaturated alcohols (geraniol and nerol). EXAFS, in situ CO-FTIR and DFT calculation results reveal that the introduction of Sn in Co-Sn IMCs dramatically optimizes the geometric and electronic structures of active Co, in which Sn isolates the Co active-site and electron transfer occurs from Sn to the Co atom. H2-TPD measurements indicate the presence of four different Co sites (labeled as α, β, γ and σ) on the surface of these IMCs; the sample of CoSn IMC shows the largest β/(γ + σ) ratio, which results in the highest selectivity toward unsaturated alcohols (SUA: 67.6%). DFT studies prove that the geometric and electronic effects of the CoSn IMC weaken the hydrogenation of the CC group, accounting for the largely enhanced hydrogenation selectivity of citral to unsaturated alcohols.
- Zhou, Junyao,Yang, Yusen,Li, Changming,Zhang, Shitong,Chen, Yudi,Shi, Shuxian,Wei, Min
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- A tandem cyclization and hydrogenation of (±)-citronellal to menthol over bifunctional Ni/Zr-beta and mixed Zr-beta and Ni/MCM-41
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The addition of nickel to Zr-beta gave a useful bifunctional catalyst that combines a high rate of cyclization of (±)-citronellal to isopulegols over zirconium sites and subsequent hydrogenation to menthols. The diastereoselectivity to the desired (±)-menthol was 90%. A loading of 4 wt% is optimal; lower loadings led to a low rate of hydrogenation, whereas a higher nickel loading appears to block the zirconium Lewis acid sites essential for the cyclization of citronellal. A mixture of Zr-beta and Ni/MCM-41 also formed an effective bifunctional catalyst system where the selectivity toward menthols remained high even with nickel loadings up to 15 wt%. The yield of (±)-menthol over the dual-catalyst system was 86-89% with 93 %, although the diastereoselectivity to (±)-menthol was lower (85%). In comparison, a 2% Pd/Zr-beta catalyst exhibited lower activity and selectivity to menthols, forming substantial amounts of 3,7-dimethyloctanal.
- Nie, Yuntong,Niah, Weilin,Jaenicke, Stephan,Chuah, Gaik-Khuan
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- catalysed Transfer Hydrogenation of Ketones and Aldehydes by Propan-2-ol
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In the presence of the cocatalyst NaOH, catalyses efficiently the transfer hydrogenation of aliphatic and aromatic ketones and aldehydes in high yields.
- Iyer, Suresh,Varghese, Jos P.
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- Continuous synthesis of menthol from citronellal and citral over Ni-beta-zeolite-sepiolite composite catalyst
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One-pot continuous synthesis of menthols both from citronellal and citral was investigated over 5 wt% Ni supported on H-Beta-38-sepiolite composite catalyst at 60–70 °C under 10–29 bar hydrogen pressure. A relatively high menthols yield of 53% and 49% and stereoselectivity to menthol of 71–76% and 72–74% were obtained from citronellal and citral respectively at the contact time 4.2 min, 70 °C and 20 bar. Citral conversion noticeably decreased with time-on-stream under 10 and 15 bar of hydrogen pressure accompanied by accumulation of citronellal, the primary hydrogenation product of citral, practically not affecting selectivity to menthol. A substantial amount of defuctionalization products observed during citral conversion, especially at the beginning of the reaction (ca. 1 h), indicated that all intermediates could contribute to formation of menthanes. Ni/H-Beta-38-sepiolite composite material prepared by extrusion was characterized by TEM, SEM, XPS, XRD, ICP-OES, N2 physisorption and FTIR techniques to perceive the interrelation between the physico-chemical and catalytic properties.
- Er?nen, Kari,M?ki-Arvela, P?ivi,Martinez-Klimov, Mark,Muller, Joseph,Murzin, Dmitry Yu.,Peurla, Markus,Simakova, Irina,Vajglova, Zuzana
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- Anionic Amphiphilic Cyclodextrins Bearing Oleic Grafts for the Stabilization of Ruthenium Nanoparticles Efficient in Aqueous Catalytic Hydrogenation
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Oleic succinyl β-cyclodextrin was proved to be efficient for the stabilization of ruthenium nanoparticles (NPs) in aqueous medium. These NPs were characterized by FTIR spectroscopy and transition electron microscopy (TEM). The catalytic activity of these NPs was evaluated in the aqueous hydrogenation of petrosourced and biosourced unsaturated compounds such as benzene and furfural derivatives. The catalytic system can be easily recycled and reused up to nine runs without any loss of activity and selectivity, demonstrating its robustness.
- Cocq, Aurélien,Léger, Bastien,No?l, Sébastien,Bricout, Hervé,Djeda?ni-Pilard, Florence,Tilloy, Sébastien,Monflier, Eric
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p. 1013 - 1018
(2019/12/27)
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- Catalytic Reductions Without External Hydrogen Gas: Broad Scope Hydrogenations with Tetrahydroxydiboron and a Tertiary Amine
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Facile reduction of aryl halides with a combination of 5% Pd/C, B2(OH)4, and 4-methylmorpholine is reported. Aryl bromides, iodides, and chlorides were efficiently reduced. Aryl dihalides containing two different halogen atoms underwent selective reduction: I over Br and Cl, and Br over Cl. Beyond these, aryl triflates were efficiently reduced. This combination was broadly general, effectuating reductions of benzylic halides and ethers, alkenes, alkynes, aldehydes, and azides, as well as for N-Cbz deprotection. A cyano group was unaffected, but a nitro group and a ketone underwent reduction to a low extent. When B2(OD)4 was used for aryl halide reduction, a significant amount of deuteriation occurred. However, H atom incorporation competed and increased in slower reactions. 4-Methylmorpholine was identified as a possible source of H atoms in this, but a combination of only 4-methylmorpholine and Pd/C did not result in reduction. Hydrogen gas has been observed to form with this reagent combination. Experiments aimed at understanding the chemistry led to the proposal of a plausible mechanism and to the identification of N,N-bis(methyl-d3)pyridin-4-amine (DMAP-d6) and B2(OD)4 as an effective combination for full aromatic deuteriation. (Figure presented.).
- Korvinson, Kirill A.,Akula, Hari K.,Malinchak, Casina T.,Sebastian, Dellamol,Wei, Wei,Khandaker, Tashrique A.,Andrzejewska, Magdalena R.,Zajc, Barbara,Lakshman, Mahesh K.
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supporting information
p. 166 - 176
(2020/01/02)
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- Hydrogenation of hydrophobic substrates catalyzed by gold nanoparticles embedded in Tetronic/cyclodextrin-based hydrogels
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Hydrogenation of alkenes, alkynes and aldehydes was investigated under biphasic conditions using Au nanoparticles (AuNP) embedded into combinations of α-cyclodextrin (α-CD) and a poloxamine (Tetronic90R4). Thermo-responsive AuNP-containing α-CD/Tetronic90R4 hydrogels are formed under well-defined conditions of concentration. The AuNP displayed an average size of ca. 7 nm and a narrow distribution, as determined by TEM. The AuNP/α-CD/Tetronic90R4 system proved to be stable over time. Upon heating above the gel-to-sol transition temperature, the studied catalytic system allowed hydrogenation of a wide range of substrates such as alkenes, alkynes and aldehydes under biphasic conditions. Upon repeated heating/cooling cycles, the Au NP/α-CD/Tetronic90R4 catalytic system could be recycled several times without a significant decline in catalytic activity.
- Chevry,Menuel,Léger,No?l,Monflier,Hapiot
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p. 9865 - 9872
(2019/07/04)
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- Recyclable cobalt(0) nanoparticle catalysts for hydrogenations
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The search for new hydrogenation catalysts that replace noble metals is largely driven by sustainability concerns and the distinct mechanistic features of 3d transition metals. Several combinations of cobalt precursors and specific ligands in the presence of reductants or under high-thermal conditions were reported to provide active hydrogenation catalysts. This study reports a new method of preparation of small, monodisperse Co(0) nanoparticles (3-4 nm) from the reduction of commercial CoCl2 in the absence of ligands or surfactants. High catalytic activity was observed in hydrogenations of alkenes, alkynes, imines, and heteroarenes (2-20 bar H2). The magnetic properties enabled catalyst separation and multiple recyclings.
- Büschelberger, Philipp,Reyes-Rodriguez, Efrain,Sch?ttle, Christian,Treptow, Jens,Feldmann, Claus,Jacobi Von Wangelin, Axel,Wolf, Robert
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p. 2648 - 2653
(2018/05/30)
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- Synthesis, characterization and performance of bifunctional catalysts for the synthesis of menthol from citronellal
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The synthesis of a series of bifunctional catalysts (1 wt% Pt/W-TUD-1 (Technische Universiteit Delft-1) and 1 wt% Pt/WO3/TUD-1) with different tungsten loadings (5-30 wt% WO3) is described. They were characterized using ICP-OES, INAA, N2 physisorption, XRD and TEM. Their catalytic performance (activity and selectivity) was evaluated in the two-step catalytic synthesis of menthol from citronellal using kinetic analysis. Introducing tungsten during the TUD-1 synthesis results in a high WO3 dispersion, essential for the acidity of the catalyst. High tungsten dispersion is also critical for the Pt hydrogenation activity. Therefore, high dispersion combined with optimal tungsten loading resulted in the highest catalytic activity. The best performing catalyst was 1 wt% Pt/W-TUD-1 (silicon to tungsten ratio of 30), with the highest yields of menthol (96%).
- Ten Dam,Ramanathan,Djanashvili,Kapteijn,Hanefeld
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p. 12041 - 12053
(2017/03/08)
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- Utilization of a Trimethylsilyl Group as a Synthetic Equivalent of a Hydroxyl Group via Chemoselective C(sp3)-H Borylation at the Methyl Group on Silicon
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A conversion of trimethylsilylalkanes into the corresponding alcohols is established based on an iridium-catalyzed, chemoselective C(sp3)-H borylation of the methyl group on silicon. The (borylmethyl)silyl group formed by C(sp3)-H borylation is treated with H2O2/NaOH, and the resulting (hydroxymethyl)silyl group is converted into a hydroxyl group by Brook rearrangement, followed by oxidation of the resulting methoxysilyl group under Tamao conditions. An alternative route proceeding through the formylsilyl group formed from a (hydroxymethyl)silyl group by Swern oxidation is also established. The method is applicable to substituted trimethylsilylcycloalkanes and 1,1-dimethyl-1-silacyclopentane for conversion into the corresponding stereodefined cycloalkyl alcohols and 1,4-butanediol.
- Torigoe, Takeru,Ohmura, Toshimichi,Suginome, Michinori
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p. 2943 - 2956
(2017/03/23)
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- Triiodide-Mediated δ-Amination of Secondary C?H Bonds
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The Cδ?H amination of unactivated, secondary C?H bonds to form a broad range of functionalized pyrrolidines has been developed by a triiodide (I3?)-mediated strategy. By in situ 1) oxidation of sodium iodide and 2) sequestration of the transiently generated iodine (I2) as I3?, this approach precludes undesired I2-mediated decomposition which can otherwise limit synthetic utility to only weak C(sp3)?H bonds. The mechanism of this triiodide-mediated cyclization of unbiased, secondary C(sp3)?H bonds, by either thermal or photolytic initiation, is supported by NMR and UV/Vis data, as well as intercepted intermediates.
- Wappes, Ethan A.,Fosu, Stacy C.,Chopko, Trevor C.,Nagib, David A.
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supporting information
p. 9974 - 9978
(2016/08/16)
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- Long-chain NHC-stabilized RuNPs as versatile catalysts for one-pot oxidation/hydrogenation reactions
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The synthesis and catalytic activity of long-chain NHC-stabilized RuNPs are presented. Full characterization of these novel nanostructures including surface state studies show that the ligand influences the number and the location of Ru active sites which impacts the NP catalytic activity, especially in hydrogenation reactions. The high stability and versatility of these nanosystems make them successful catalysts for both oxidation and hydrogenation reactions that can even be performed successively in a one pot-fashion.
- Martínez-Prieto,Ferry,Rakers,Richter,Lecante,Philippot,Chaudret,Glorius
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supporting information
p. 4768 - 4771
(2016/04/09)
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- Hydromethylation of Unactivated Olefins
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A solution to the classic unsolved problem of olefin hydromethylation is presented. This highly chemoselective method can tolerate labile and reactive chemical functionalities and uses a simple set of reagents. An array of olefins, including mono-, di-, and trisubstituted olefins, are all smoothly hydromethylated. This mild protocol can be used to simplify the synthesis of a specific target or to directly "edit" complex natural products and other advanced materials. The method is also amenable to the simple installation of radioactive and stable labeled methyl groups.
- Dao, Hai T.,Li, Chao,Michaudel, Quentin,Maxwell, Brad D.,Baran, Phil S.
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supporting information
p. 8046 - 8049
(2015/07/15)
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- Hydrogenation of citral in a solvent
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The present invention is concerned with a novel and improved process for the manufacture of tetrahydrogeraniol by hydrogenation of citral in a solvent.
- -
-
Paragraph 0022; 0023; 0024; 0025
(2014/08/20)
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- Highly selective menthol synthesis by one-pot transformation of citronellal using Ru/H-BEA catalysts
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The one-pot transformation of citronellal to menthol requires a combined cyclization-hydrogenation step for which Ru/H-BEA catalysts were identified as highly active and selective catalysts. After identifying zeolite H-BEA as the most promising heterogeneous catalyst for the cyclization of citronellal to the intermediate isopulegol, bifunctional metal/H-BEA catalysts were investigated in the one-pot transformation of citronellal to menthols. Using Pd undesired defunctionalization prevailed, while using Pt and Ru, the formation of menthols predominated. Finally, for Ru/H-BEA catalysts, the effect of catalyst composition (Si:Al ratio, Ru content) and reaction conditions (temperature, hydrogen pressure, and solvent) was investigated to diminish citronellal hydrogenation, dimerization, and defunctionalization. Accordingly, with a 1%Ru/H-BEA-25 catalyst (Ru particle size = 1 nm) in dioxane at 15 bar hydrogen pressure and 373 K, a very high selectivity to menthols of 93% at nearly full conversion was obtained. The catalyst is also highly diastereoselective producing 79% of the desired (±)-menthol.
- Pl?sser, Jutta,Lucas, Martin,Claus, Peter
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p. 189 - 197
(2015/09/28)
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- Immobilization of palladium catalyst on magnetically separable polyurea nanosupport
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This work describes a method for preparing magnetic polyurea nanoparticles (PU NPs) and their utilization as a catalyst support. The method is based on entrapment of hydrophilic magnetic nanoparticles within the polyurea matrix. The synthetic process of these magnetic polyurea nanoparticles is based on oil-in-oil nanoemulsification of an organic polar phase comprised of N,N-dimethylacetamide (DMAc), 2,6-diaminopyridine and ionic liquid modified magnetite nanoparticles (MNPs-IL), in heptane containing a suitable surfactant. This was followed by interfacial polycondensation reaction between an isocyanate monomer, polymethylenepolyphenyl isocyanate (PAPI 27), and the amine monomer producing magnetically separable polyurea nanoparticles. Subsequently, these particles were employed as a catalyst nanosupport. Two catalytic systems based on the encapsulation of Pd(OAc)2 within magnetic PU NPs or their adsorption on the surface of these particles were produced and subjected to hydrogenation reactions and selective hydrogenations of α,β-unsaturated compounds. Pd(OAc)2 adsorbed on the surface of the magnetic PU NPs demonstrated high catalytic activity and selectivity, which was superior to the conventional catalyst Pd/C or palladium nanoparticles supported directly on the surface of magnetite nanoparticles. The catalyst was easily recovered from the reaction mixture by applying an external magnetic field and recycled over five times without observing any significant loss in its catalytic efficiency. This journal is
- Natour, Suzana,Abu-Reziq, Raed
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p. 48299 - 48309
(2014/12/10)
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- Core-shell AgNP@CeO2 nanocomposite catalyst for highly chemoselective reductions of unsaturated aldehydes
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Selective silver: A core-shell AgNP-CeO2 nanocomposite (AgNP@CeO2) acted as an effective catalyst for the chemoselective reductions of unsaturated aldehydes to unsaturated alcohols with H2 (see figure). Maximizing the AgNP-CeO2 interaction successfully induced the heterolytic cleavage of H2, resulting in highly chemoselective reductions. Furthermore, a highly dispersed AgNP@CeO2 system was also developed that exhibited a higher activity than the original AgNP@CeO2. Copyright
- Mitsudome, Takato,Matoba, Motoshi,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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supporting information
p. 5255 - 5258
(2013/05/22)
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- Selective reduction of dienes/polyenes using sodium borohydride/catalytic ruthenium(III) in various liquid amide aqueous mixtures
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An efficient method to effect selective reduction of several structurally diverse dienes and an unsymmetrical triene is reported. The reduction is facile at 0 °C in a liquid amide aqueous solution containing sodium borohydride in the presence of 15 mol % ruthenium(III) chloride. The chemoselectivity of the reaction is controlled by proper choice of the liquid amide solvent.
- Babler, James H.,Ziemke, David W.,Hamer, Robert M.
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p. 1754 - 1757
(2013/04/10)
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- Reduction of citral in water under typical transfer hydrogenation conditions-Reaction mechanisms with evolution of and hydrogenation by molecular hydrogen
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The reduction of an α,β-unsaturated aldehyde, citral, was investigated over a 10 wt% Pd catalyst under transfer hydrogenation (TH) conditions in a closed system with microwave assistance. Surprisingly, it was found that hydrogen was produced quite fast under the microwave irradiation during the reaction, and the reduction of citral was proved to go mainly through consecutive pathways of hydrogen production - hydrogenation rather than those commonly considered for TH reactions. Similar reaction pathways were also observed with a homogeneous catalyst of [RuCl2(C6H 6)]2 and other typical hydrogen donors like formate salts and isopropanol, which are usually used in the typical transfer hydrogenations.
- Liu, Ruixia,Wang, Yu,Cheng, Haiyang,Yu, Yancun,Zhao, Fengyu,Arai, Masahiko
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p. 315 - 320
(2013/02/23)
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- Micro and nanobubble based strategy for gas-liquid-solid multiphase reactions: Palladium-catalysed hydrogenation of carbon-carbon unsaturated bonds
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An autoclave-free, gas-liquid-solid multiphase hydrogenation of carbon-carbon unsaturated bonds using hydrogen micro and nanobubbles (MNBs) is developed. The process allows the liquid phase of the reaction mixture to maintain a high concentration of hydrogen gas. Georg Thieme Verlag Stuttgart New York.
- Mase, Nobuyuki,Isomura, Shogo,Toda, Mitsuo,Watanabe, Naoharu
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supporting information
p. 2225 - 2228
(2013/11/06)
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- Iron(III) chloride-catalysed aerobic reduction of olefins using aqueous hydrazine at ambient temperature
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A chemoselective reduction of olefins and acetylenes is demonstrated by employing catalytic amounts of ferric chloride hexahydrate (FeCl 3·6 H2O) and aqueous hydrazine (NH 2NH2·H2O) as hydrogen source at room temperature. The reduction is chemoselective and tolerates a variety of reducible functional groups. Unlike other metal-catalysed reduction methods, the present method employs a minimum amount of aqueous hydrazine (1.5-2 equiv.). Also, the scope of this method is demonstrated in the synthesis of ibuprofen in aqueous medium. Copyright
- Lamani, Manjunath,Ravikumara, Guralamata S.,Prabhu, Kandikere Ramaiah
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supporting information; experimental part
p. 1437 - 1442
(2012/07/03)
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- Citral hydrogenation over Rh and Pt catalysts supported on TiO2: Influence of the preparation and activation protocols of the catalysts
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During citral hydrogenation, the products distribution obtained on Rh/TiO2 and Pt/TiO2 catalysts depends on their preparation and activation protocols: (i) the unsaturated alcohols (the intended products) are formed in higher quantity on samples reduced at 500 °C and more notably with Pt/TiO2 catalyst; (ii) samples prepared by impregnation of the metallic precursor salt in HCl medium and activated at 300 °C are the only ones to lead to the formation of isopulegol as by-product. On the catalysts activated at 500 °C, these results can be explained by the presence of the SMSI effect beneficial to hydrogenate selectively the CO bond of citral towards unsaturated alcohols.
- Ekou, Tchirioua,Ekou, Lynda,Vicente, Aurélie,Lafaye, Gwendoline,Pronier, Stéphane,Especel, Catherine,Marécot, Patrice
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experimental part
p. 82 - 88
(2011/04/18)
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- Pd-MCM-48: A novel recyclable heterogeneous catalyst for chemo- and regioselective hydrogenation of olefins and coupling reactions
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A novel, heterogeneous Pd-MCM-48 catalyst has been developed by encapsulating palladium nanoparticles into the cubic phase of mesoporous MCM-48 matrix at room temperature. The catalyst demonstrated excellent chemo- and regioselectivity for the hydrogenation of olefins at room temperature within 30-80 min. The turnover frequency for the hydrogenation is very high (4400 h-1). Interestingly, selectivity of the catalyst was significantly influenced by the mode of addition of palladium precursor. Moreover, the catalyst was also very effective for the coupling reactions with the formation of carbon-carbon and carbon-nitrogen bonds under ligand-free and aerobic conditions.
- Banerjee, Subhash,Balasanthiran, Vagulejan,Koodali, Ranjit T.,Sereda, Grigoriy A.
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scheme or table
p. 4316 - 4321
(2010/11/04)
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- METHOD FOR PREPARING ORTHO-SUBSTITUTED AMINOFERROCENES
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The present disclosure relates to a method for preparing an ortho-substituted aminoferrocene comprising reacting an aminoferrocene with a Lewis acid and a lithiating reagent in the presence of an electrophile to form the ortho-substituted aminoferrocene.
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Page/Page column 22
(2010/06/16)
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- A convenient methodology for the chemoselective reduction of a wide variety of functionalized alkenes
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An efficient method to effect chemoselective reduction of alkenes (including trisubstituted olefins) possessing various sensitive and/or reducible groups such as acetals, allylic alcohols, benzyl ethers, epoxides, esters, halides, nitriles, and sulfones is reported. The reduction is facile at 0 °C in aqueous N,N-dimethylacetamide containing sodium borohydride in the presence of 15 mol % ruthenium(III) chloride. Regioselective reduction of dienes is also feasible if the double bonds are sufficiently different in their structural environment.
- Babler, James H.,White, Nicholas A.
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experimental part
p. 439 - 441
(2010/03/04)
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- A useful, reliable and safer protocol for hydrogenation and the hydrogenolysis of o-benzyl groups: The in situ preparation of an active Pd 0/C catalyst with well-defined properties
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A simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O-benzyl ethers has been developed. The method features the in situ preparation of an active Pd0/C catalyst from Pd(OAc)2 and charcoal, in methanol. The mild reaction conditions (25°C) and low catalyst loading required (0.025 mol%), as well as the absence of contamination of the product by palladium residues (0/C: It's a kind of magic! A sustainable, simple and highly reproducible protocol for the hydrogenation of alkenes and alkynes (see scheme) and for the hydrogenolysis of O-benzyl ethers has been developed with an in situ generated Pd0/C catalyst. The homemade Pd0/C catalyst allows mild reaction conditions (25°C, 1 atm H2) and low catalyst loading (as low as 0.025 mol%), without any contamination of the product by palladium residues (4 ppb).
- Felpin, Francois-Xavier,Fouquet, Eric
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supporting information; experimental part
p. 12440 - 12445
(2011/01/05)
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- Colloidal palladium nanoparticles with in situ H2: Reducing system for ,-unsaturated carbonyl compounds
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A new reducing system comprising Pd(OAc)2 and NaBH4 in methanol to generate palladium nanoparticles has been efficiently utilized to reduce a variety of unsaturated carbonyl compounds. These were reduced to their corresponding saturated alcohols and fully saturated compounds in selected cases. This protocol presents alternative and mild reaction conditions for reduction.
- De Castro, Kathlia A.,Oh, Seungchan,Yun, Jongchan,Lim, Jin Kyu,An, Gwangil,Kim, Dong Kook,Rhee, Hakjune
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experimental part
p. 3509 - 3520
(2009/12/05)
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- Zr-zeolite beta: A new heterogeneous catalyst system for the highly selective cascade transformation of citral to (±)-menthol
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The transformation of citral to menthols involves hydrogenation steps as well as cyclisation of the intermediate, citronellal. The ability of Zrzeolite beta to catalyse the cyclisation with high diastereoselectivity to (±)-isopulegol is the critical step
- Nie, Yuntong,Jaenicke, Stephan,Chuah, Gaik-Khuan
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experimental part
p. 1991 - 1999
(2009/09/06)
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- Hydrogenation of C-C multiple bonds mediated by [Pd(NHC)(PCy3)] (NHC = N-heterocyclic carbene) under mild reaction conditions
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A study was conducted to demonstrate the behavior of a Pd 0-N-heterocyclic carbene (NHC) complex under hydrogen (H2) and its catalytic performance in hydrogenation of C-C multiple bonds. It was also demonstrated that [Pd(SIPr)(PCy3) solution was a highly active catalyst for the hydrogenation of a wide range of alkenes and alkynes using H2. It was observed that [Pd(SIPr)(PCy 3) underwent an oxidative addition, leading to the trans-dihydride species [Pd(H2)(SIPr))(PCy3). The presence of the species was also supported by1H NMR spectroscopy investigations. It was also demonstrated that the catalytic system was efficient for functionalized and non-functionalized terminal and internal alkenes.
- Jurcik, Vaclav,Nolan, Steven P.,Cazin, Catherine S. J.
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supporting information; experimental part
p. 2509 - 2511
(2009/11/30)
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- A Convenient access to (All-rac)-α-tocopherol acetate from linalool and dihydromyrcene
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Refluxing trimethylhydroquinone 2 in 10:1 dodecane/CH2Cl 2 with linalool 3b (two-fold excess) and camphorsulfonic acid, then treating the crude condensation product (consisting of a mixture of the chromanols 1b and 1c, alongside the tricyclic compounds 9 and 10) sequentially with Ac2O and m-CPBA afforded, after removal by column chromatography of the 9/10 acetates, a mixture of the regioisomeric epoxides 1jOAc and 1kOAc (ratio 9:1, total 60%). Treatment of this mixture with Al(O-i-Pr)3 followed by CuI-catalysed Wurtz coupling of the acetates of the resulting allylic alcohols with citronellylmagnesium chloride 12a, and finally hydrogenation then provided the title acetate (overall 46% from 2).
- Gembus, Vincent,Sala-Jung, Nathalie,Uguen, Daniel
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experimental part
p. 829 - 842
(2009/12/25)
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- Ionene-bound borohydrides: Efficient, selective, and versatile polymer-supported reducing agents
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Reduction of structurally different carbonyl compounds, such as aldehydes, ketones, α,β-unsaturated enals and enones, acid chlorides, and imines was accomplished efficiently using high capacity ionene based borohydride reagents. Aldehydes and imines were reduced to the corresponding alcohols and amines in excellent yields in methanol at ambient temperature while ketones and acid chlorides were reduced in iso-propanol and THF-MeOH at reflux. Chemoselective reduction of aldehydes over ketones was achieved successfully with these reagents. Complete regioselectivity was also observed in the reduction of α,β-unsaturated aldehydes and ketones.
- Lakouraj, Moslem M.,Tajbakhsh, Mahmood,Mahalli, Majid S.
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p. 117 - 123
(2008/09/21)
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- Reduction of carbon-carbon double bonds using organocatalytically generated diimide
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(Chemical Equation Presented) An efficient method has been developed for the reduction of carbon-carbon double bonds with diimide, catalytically generated in situ from hydrazine hydrate. The employed catalyst is prepared in one step from riboflavin (vitamin B2). Reactions are carried out in air and are a valuable alternative when metal-catalyzed hydrogenations are problematic.
- Smit, Christian,Fraaije, Marco W.,Minnaard, Adriaan J.
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supporting information; experimental part
p. 9482 - 9485
(2009/04/06)
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- Simple and efficient microwave-assisted hydrogenation reactions at moderate temperature and pressure
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A generally applicable method for the introduction of gaseous hydrogen into a sealed reaction system to perform hydrogenation reactions under microwave irradiation has been developed. Several different types of substrates are easily reduced in short reaction times with moderate temperatures between 80 °C and 100 °C with 50 psi of hydrogen. The use of simultaneous cooling is also applied to the hydrogenation of more difficult substrates. Georg Thieme Verlag Stuttgart.
- Vanier, Grace S.
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p. 131 - 135
(2008/03/13)
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- Method and apparatus for conducting microwave assisted organic reactions with gas-phase reactants
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A method of accelerating the hydrogenation of organic compounds is provided. The method includes positioning an microwave transparent reaction vessel containing at least one reactant suitable for hydrogenation in a microwave cavity, purging the reaction vessel, charging the reaction vessel with hydrogen gas, and applying a continuous single mode of microwave radiation within the cavity and to the vessel and its contents for a time sufficient to effect a chemical change in the reactants.
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Page/Page column 6
(2008/06/13)
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- Dihydrogen reduction of carboxylic esters to alcohols under the catalysis of homogeneous ruthenium complexes: High efficiency and unprecedented chemoselectivity
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(Chemical Equation Presented) The missing link: The presence of two N,P bridges in the ruthenium complexes used as catalysts for the title reaction is essential. Esters that contain isolated C=C bonds are reduced to the corresponding unsaturated alcohols in high yields with high chemoselectivity (see example).
- Saudan, Lionel A.,Saudan, Christophe M.,Debieux, Catherine,Wyss, Patrick
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p. 7473 - 7476
(2008/09/18)
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- Improved method for the diimide reduction of multiple bonds on solid-supported substrates
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(Chemical Equation Presented) A mild and improved method for reducing multiple bonds on various resins with diimide is described. The simple procedure readily generates diimide from 2-nitrobenzenesulfonohydrazide and triethylamine at room temperature. A number of representative multiple bonds in various steric and electronic environments were examined, including polar double bonds such as carbonyl and azo, for ease and selectivity of reduction. A general trend of reactivity was identified which revealed, inter alia, that terminal olefins, 1,2-disubstituted olefins, electron-poor olefins, and terminal alkynes were the most easily reduced.
- Buszek, Keith R.,Brown, Neil
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p. 3125 - 3128
(2008/02/07)
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- Hybrid bidentate ligand for functional recognition: An application to regioselective C=C double bond hydrogenation
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Regioselectivity increases in C=C double bond hydrogenation could be obtained for Lewis basic substrates on a Lewis acidic support by using a rhodium complex supported on a mesoporous solid. The Royal Society of Chemistry 2006.
- Goettmann, Frederic,Le Floch, Pascal,Sanchez, Clement
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p. 2036 - 2038
(2008/09/18)
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- Potential therapeutic antioxidants that combine the radical scavenging ability of myricetin and the lipophilic chain of vitamin E to effectively inhibit microsomal lipid peroxidation
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The flavonol myricetin, reacts with oxygen-centred galvinoxyl radicals 28 times faster than d-α-tocopherol (vitamin E), the main lipid-soluble antioxidant in biological membranes. Moreover, each myricetin molecule reduces twice as many such radicals as vitamin E. However, myricetin fails to protect vitamin E-deficient microsomes from lipid peroxidation as assessed by the formation of thiobarbituric acid reactive substances (TBARS). Novel and potentially therapeutic antioxidants have been prepared that combine the radical-scavenging ability of a myricetin-like head group with a lipophilic chain similar to that of vitamin E. C6-C12 alkyl chains are attached to the A-ring of either a 3,3′,4 ′,5′-tetrahydroxyflavone or a 3,2 ′,4′,5′-tetrahydroxyflavone head group to give lipophilic flavonoids (ClogP=4 to 10) that markedly inhibit iron-ADP catalysed oxidation of microsomal preparations. Orientation of the head group as well as total lipophilicity are important determinants of antioxidant efficacy. MM2 models indicate that our best straight chain 7-alkylflavonoids embed to the same depth in the membrane as vitamin E. The flavonoid head groups are prepared by aldol condensation followed by Algar-Flynn-Oyamada (AFO) oxidation or by Baker-Venkataraman rearrangement. The alkyl tails are introduced by Suzuki or Negishi palladium-catalysed cross-coupling or by cross-metathesis catalysed by first generation Grubbs catalyst, which tolerate phenolic hydroxyl and ketone groups.
- Bennett, Christopher J.,Caldwell, Stuart T.,McPhail, Donald B.,Morrice, Philip C.,Duthie, Garry G.,Hartley, Richard C.
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p. 2079 - 2098
(2007/10/03)
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