- A novel and efficient catalytic epoxidation of olefins and monoterpenes with microencapsulated Lewis base adducts of methyltrioxorhenium
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The reactivity of methyltrioxorhenium in the epoxidation of olefins can be tuned by the presence of Lewis bases as ligands of the metal center. Unfortunately, a large excess of ligand is usually required to obtain high yields and selectivities mainly because of the fluxional behaviour that these compounds show in solution. We describe here the microencapsulation technique that can resolve this problem. Microencapsulated Lewis base adducts of methyltrioxorhenium with nitrogen containing ligands are highly efficient and selective catalysts for the epoxidation of several olefins and monoterpenes with hydrogen peroxide even in the case of the most sensitive substrates. These systems show the advantages of the ligand accelerated catalysis and the benefits of heterogeneous compounds. They can be easily recovered from the reaction mixture and used for more transformations.
- Saladino, Raffaele,Andreoni, Alessia,Neri, Veronica,Crestini, Claudia
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- Photocatalytic oxygenation of hydrocarbons with (tetraarylporphyrinato)iron(III) complexes and molecular oxygen. Comparison with microsomal cytochrome P-450 mediated oxygenation reactions
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Photocatalytic oxygenation of various alkenes with dioxygen and (5,10,15,20-tetraarylporphyrinato)iron(III) complexes yielded allylic oxygenation products and/or epoxides. The product composition was found to be influenced both by the nature of the used substrate and by the concentrations, as well as the axial ligands. Alkenes with strained carbon double bonds gave preferentially epoxides whereas mainly allylic oxygenation was observed for unstrained alkenes. The proposed reaction mechanisms involve the oxoiron(IV) porphyrinate (P)FeIV=O as the catalytically active species whose selectivity is related to that of the oxygenation of α-pinene with microsomal cytochromes P-450 and P-420 obtained from the yeast strain Torulopsis apicola. Oxygenation products observed with both systems give evidence for the occurrence of an oxoiron(IV) heme species in microsomal cytochrome P-450 mediated reactions. The enantio-, regio-, and chemoselectivities of the photooxygenation with iron(III) porphyrins and molecular oxygen are explained in terms of abstraction of an allylic hydrogen atom, catalyzed autoxidation and "direct" oxygen-transfer reactions.
- Weber,Hommel,Behling,Haufe,Hennig
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- Enantiospecific synthesis, separation and olfactory evaluation of all diastereomers of a homologue of the sandalwood odorant Polysantol
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The four stereoisomers of (5E)-4,4-dimethyl-6-(2′,2′,3′- trimethylcyclopent-3′-en-1′-yl)-hex-5-en-3-ol, a homologue of the valuable sandalwood-type odorant Polysantol, were enantiospecifically synthesized from (+)- and (-)-α-pinene, through (-)- and (+)-campholenic aldehyde, by aldol condensation with 3-pentanone, deconjugative α-methylation and reduction. The mixtures of epimeric alcohols obtained after reduction were separated by means of derivatization with (-)-(1S)-camphanic chloride. The enantiomerically pure final products were evaluated organoleptically.
- Castro, Juan M.,Linares-Palomino, Pablo J.,Salido, Sofía,Altarejos, Joaquín,Nogueras, Manuel,Sánchez, Adolfo
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- Aerobic epoxidation of natural terpenes: Study of the catalytic activity of new Ru-1,2,4-triazepine compelxes
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Aerobic epoxidation of a range of natural terpenic olefines was carried out by using the triazepinic complexes [RuCl(TAZO)(p-cymene)] C1 and [Ru(TAZS)(p-cymene)]2 C2, recently prepared from [RuCl2(p-cymene)]2 and the corresponding 1,2,4-triazepines (HTAZO and H2TAZS). While, good similar stereoselectivity was observed for the two complexes, C1 was shown to be more effective and chemioselective.
- Fdil, Na?ma,Ait Itto, My Youssef,Ait Ali, Mustapha,Karim, Abdellah,Daran, Jean-Claude
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- Manganese(III) porphyrin catalysts for the oxidation of terpene derivatives: A comparative study
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A comparative study involving four manganese(III) porphyrin catalysts combined with two different oxidants (sodium hypochlorite and potassium monopersulfate) has been performed in the epoxidation of three terpene derivatives. The catalytic oxidation of α-pinene produces selectively 100% of the epoxide or 65% of allylic oxidation products, only by modification of the substituents on the meso-positions of the metalloporphyrin catalyst. The catalytic oxidation of the 5-vinyl-2-norbornene is regio- and stereoselective, producing only the exo-2,3-epoxy-5-vinylnorbornane. With α-terpinene, a conjugated di-olefin, an oxidative dehydrogenation reaction was surprisingly observed, producing p-cymene as a major compound.
- Maraval, Valerie,Ancel, Jean-Erick,Meunier, Bernard
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- Opening of epoxide rings catalyzed by niobium pentachloride
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The behavior of several epoxides when treated with NbCl5 was studied. In general, the studied epoxides reacted rapidly with NbCl5, giving, in most cases, more than one product (chlorohydrins, products containing solvent residues, as well as rearrangement products). A detailed study was performed to verify the effects of the temperature (rt, 0°C, or -78°C) and of the NbCl5 molar concentration on the composition of the products, yield, and time required for the reactions. Copyright Taylor & Francis Group, LLC.
- Constantino, Mauricio Gomes,Lacerda Jr., Valdemar,Invernize, Paulo Roberto,Filho, Luiz Carlos Da Silva,Da Silva, Gil Valdo Jose
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p. 3529 - 3539
(2008/03/13)
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- Reactions of epoxides prepared from some monoterpenes with acetic anhydride on aluminosilicate catalysts
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Reactions of epoxides prepared from α-, β-pinenes and camphene with acetic anhydride on aluminosilicate catalysts (clay K-10, zeolite β) were investigated affording various products of skeleton rearrangements: mono- and diacetates with five- and six-membered rings, and also with norbornane and pinane cores.
- Tatarova,Korchagina,Volcho,Salakhutdinov,Barkhash
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p. 1076 - 1082
(2007/10/03)
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- Substrate-induced diastereoselectivity in the dimethyldioxirane epoxidation of simple alkenes and dienes
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Various alkenes and dienes, such as (R)- or (S)-limonene 2, 2-carene 6, 3-carene 8, (R)-α-pinene 10, (S)-α-pinene 12, and endo-dicyclopentadiene 14 were transformed into the corresponding mono- and bis-epoxides by epoxidation with dimethyldioxirane (as an acetone solution). The selectivity observed in these epoxidations is explained by the assumption of hydrogen bonding between bridge protons and the dioxirane.
- Asouti,Hadjiarapoglou
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p. 1847 - 1850
(2007/10/03)
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- Diastereoselective epoxidation of olefins by organo sulfonic peracids, II
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We have investigated the behaviour of sulfonic peracids 2 in situ generated towards olefins 7a, 7b, 9, 11, 14, 16, 18, allylic acid and homoallylic alcohols 20, 22, 24, 26, 28, 30, 33 and α,β-unsaturated ketones 35, 37, 39. Generally, the epoxidation proceeds in a peracid-like manner with greater diastereoselectivity than those by common oxidants. In particular, the epoxidation of Δ4 3-ketosteroids 39a-i led to 4α,5α-epoxides 40a-i with remarkable high de-values. Enhanced α-selectivity was also found in the epoxidation of cholesterol 28b. Due to the mild reaction conditions, even acid sensitive epoxides 8a, 8b, 10, 12, 13, 15, 17, 19 were obtained in good yields.
- Kluge,Schulz,Liebsch
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p. 2957 - 2976
(2007/10/03)
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- Sulfonic peracids - III. Heteroatom oxidation and chemoselectivity
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We have investigated the p-toluenesulfonic peracid (2) generated in situ in the oxidation of different types of compounds containing nitrogen and/or sulfur. The sulfonic peracid 2 shows a remarkable chemoselectivity characterized by a preferred oxidation of sulfides to the sulfones in the presence of amines or olefins and a strong dependence on the nature of the amine in the competitive oxidation of olefins and amines.
- Kluge,Schulz,Liebsch
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p. 5773 - 5782
(2007/10/03)
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- INTRODUCTION OF OXYGENATED FUNCTIONAL GROUPS INTO 3-CARENE AND 2-PINENE BY CULTURED CELLS
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The biotransformation of the monoterpene hydrocarbons 3-carene and 2-pinene by cell suspension cultures of Nicotiana tabacum and Catharanthus roseus was investigated.The cultures have the ability to regio- and enantioselectively introduce the oxygenated functional groups into the C=C double bond and the allylic positions of the substrates. - Key words: Nicotiana tabacum; Solanaceae; Catharanthus roseus; Apocyanaceae; cultured cells; biotransformation; epoxidation; hydroxylation; carene; pinene.
- Hirata, Toshifumi,Ikeda, Yoshihiro,Izumi, Shunsuke,Shimoda, Kei,Hamada, Hiroki,Kawamura, Toshinari
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p. 401 - 404
(2007/10/02)
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- Photocatalytic Enantiodiscriminating Oxygenation with Cyclodextrin-linked Porphyrins and Molecular Oxygen
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2,6-Permethylated β-cyclodextrin-linked iron and manganese porphyrins catalyse the enantioselective oxygenation of racemic mixture of (S)-α-pinene and (R)-α-pinene with molecular oxygen under irradiation with visible light.
- Weber, Lutz,Imiolczyk, Ines,Haufe, Guenter,Rehorek, Detlef,Hennig, Horst
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p. 301 - 303
(2007/10/02)
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- NaOCl OLEFIN EPOXIDATIONS CATALYZED BY Mn-PORPHYRINS UNDER TWO-PHASE CONDITIONS. INFLUENCE OF STRUCTURAL FACTORS ON THE STABILITY, CATALYTIC ACTIVITY AND SELECTIVITY OF PORPHYRINS
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The progressive deactivation of a series of Mn-tetraarylporphyrins (TPP, TMP, TAP, TPFPP, TDClPP), which are very efficient catalysts for olefin epoxidations, has been measured under the reaction conditions.Reactions are carried out at 0 deg C in CH2Cl2-H2O, with NaOCl aqueous solution at pH 9.5, in the presence of N-hexyl imidazole as an axial ligand and, generally, of a phase-transfer catalyst.All porphyrins are more or less rapidly deactivated, the only exception being Mn-TDClPP which can be almost quantitatively recovered.Both steric and electronic effects seem therefore to be essential for the chemical stability of metallo-porphyrins.In the presence of 0.005 molar equivalents of Mn-TDClPP, α-olefins and sterically unhindered internal olefins are epoxidized in high yields at 0 deg C and very short reaction times.Highly regio- and stereo-selective oxidations can be also achieved.
- Banfi, Stefano,Montanari, Fernando,Penso, Michele,Sosnovskikh, Viecheslav,Vigano, Patrizia
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p. 689 - 694
(2007/10/02)
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- Stereocontrolled Regiospecificity of the Water Loss from trans-Sobrerol Radical Cation upon Electron Ionization
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Water loss from trans-sobrerol upon electron impact ionization selectively involves the tertiary OH group, predominantly occuring by a stereocontrolled H-transfer from C(5) position in a rate-determining step process, as proved by 18O and deuterium labelling.Monomethyl ethers behave accordingly.Ionic structures of the water-loss product or products are investigated by metastable ion and collision activation mass-analysed ion kinetic energy spectroscopy, using model ions generated from some substrates, which are chemically related to trans-sobrerol in condensed phase, i.e. α-pinane epoxide, cis-sobrerol and pinol.A substantial conversion of cis-sobrerol molecular ions to ionized pinol by loss of water has been demonstrated.
- Selva, Antonio,Ferrario, Francesco,Ventura, Paolo,Pellegata, Renato
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p. 523 - 529
(2007/10/02)
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- Chromic Acid Oxidation of Some Oxiranes
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Oxiranes derived from some alkenes, with olefinic bonds present in different stereoelectronic environments, have been treated with Cr(VI)-reagents.The major products obtained have been identified and their formation rationalized.In some cases, the method becomes synthetically useful for C-C bond cleavage.
- Krishna, R. R.,Chawla, H. P. S.,Dev, Sukh
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p. 1190 - 1196
(2007/10/02)
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- STEREOCHEMICAL ARGUMENTS AGAINST A POSSIBLE CHLOROHYDRIN ROUTE IN THE CATALYTIC EPOXIDATION OF OLEFINS WITH NaOCl/Mn-porphyrins.
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The stereochemistry of the epoxidation of norbornene and 3-carene with the NaOCl/Mn(TPP)OAc system is the same as that observed with peracids, suggesting that the chlorohydrin route does not occur in this catalytic epoxidation.
- Carvalho, Maria-Eliza De,Meunier, Bernard
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p. 3621 - 3624
(2007/10/02)
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