- PREPARATIVE SYNTHESIS OF ISOPRENE OXIDE
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The reaction of isoprene, hydrogen peroxide, and commercial hydrobromic acid gives 1-bromo-2-methyl-3-buten-2-ol, the low-temperature dehydrobromination of which gives isoprene oxide in high yield.
- Arakelyan, A. S.,Dvoryanchikov, A. I.,Gevorkyan, A. A.
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- Enantioselective total synthesis of the reported structures of (-)-9-epi-presilphiperfolan-1-ol and (-)-presilphiperfolan-1-ol: Structural confirmation and reassignment and biosynthetic insights
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When epi isn't. The first total synthesis of the reported structures of 9-epi-presilphiperfolan-1-ol and presilphiperfolan-1-ol has been achieved. Key steps are a catalytic asymmetric alkylation of a novel diene-containing electrophile followed by a two-carbon ring contraction and an intramolecular Diels-Alder cycloaddition to form the stereochemically dense tricyclic core. The synthetic work has resulted in the structural revision of presilphiperfolan-1- ol (see scheme). Copyright
- Hong, Allen Y.,Stoltz, Brian M.
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- Total synthesis and absolute configuration assignment of MRSA active garcinol and isogarcinol
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A short total synthesis of (±)-garcinol and (±)-isogarcinol, two endo-type B PPAPs with reported activity against methiciline resistant Staphylococcus aureus (MRSA), is presented. The separation of framework-constructing from framework-decorating steps and the application of two highly regio- and stereoselective Pd-catalysed allylations, that is, the Pd-catalysed decarboxylative Tsuji-Trost allylation and the diastereoselective Pd-catalysed allyl-allyl cross-coupling, are key elements that allowed the total synthesis to be accomplished within 13 steps starting from acetylacetone. After separation of the enantiomers the absolute configurations of the four natural products (i.e., (-)-garcinol, (+)-guttiferone E (i.e., ent-garcinol), (-)-isogarcinol, and (+)-isoxanthochymol (i.e., ent-isogarcinol)) were assigned based on ECD spectroscopy.
- Socolsky, Cecilia,Plietker, Bernd
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- Epoxide formation in the reactions of the nitrate radical with 2,3-dimethyl-2-butene, cis- and trans-2-butene and isoprene
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Epoxide formation in the nighttime reaction of NO3 with 2,3-dimethyl-2-butene, cis- or trans-2-butene or isoprene was studied in a 480 l reaction chamber with in situ FTIR spectroscopy as analytical technique. Most experiments were carried out at either 20 Torr in argon or at 740 Torr in synthetic air. In the case of 2,3-dimethyl-2-butene the epoxide formation was studied in the range 20-740 Torr using either argon or air as diluent gas and its O2 dependence was studied in N2/O2 mixtures with O2 concentrations in the range 1.7 x 1015-4.9 x 1018 molec cm-3, at a total pressure of 740 Torr. In the experiments performed at 20 Torr in argon, epoxides were found in all reactions as main products. The measured molar yields were 95.3% for 2,3-dimethyl-2-butene, 50% for cis- and trans-2-butene and 20% for isoprene. In the experiments performed at 740 Torr air, epoxides were below the detection limit in the case of cis- and trans-2-butene and isoprene, whereas a yield of 17.4% of the epoxide was measured in the 2,3-dimethyl-2-butene experiments. Possible reaction mechanisms explaining the experimental results are discussed. Epoxide formation in the nighttime reaction of NO3 with 2,3-dimethyl-2-butene, cis- or trans-2-butene or isoprene was studied in a 480 l reaction chamber with in situ FTIR spectroscopy as analytical technique. Most experiments were carried out at either 20 Torr in argon or at 740 Torr in synthetic air. In the case of 2,3-dimethyl-2-butene the epoxide formation was studied in the range 20-740 Torr using either argon or air as diluent gas and its O2 dependence was studied in N2/O2 mixtures with O2 concentrations in the range 1.7 × 1015-4.9 × 1018 molec cm-3, at a total pressure of 740 Torr. In the experiments performed at 20 Torr in argon, epoxides were found in all reactions as main products. The measured molar yields were 95.3% for 2,3-dimethyl-2-butene, 50% for cis- and trans-2-butene and 20% for isoprene. In the experiments performed at 740 Torr air, epoxides were below the detection limit in the case of cis- and trans-2-butene and isoprene, whereas a yield of 17.4% of the epoxide was measured in the 2,3-dimethyl-2-butene experiments. Possible reaction mechanisms explaining the experimental results are discussed.
- Skov,Benter Th.,Schindler,Hjorth,Restelli
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- Synthetic studies on pseudolaric acid B: Enantioselective synthesis of C4,C10-di-epi-trans-fused [5-7]-bicyclic skeleton
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Studies on the synthesis of antifungal and anticancer natural product, pseudolaric acid B, have led to the enantioselective synthesis of di-epi-trans-fused [5–7]-bicyclic core skeleton. The synthesis was achieved in 10 linear steps, which features the Sharpless asymmetric epoxidation, cyanide-opening reaction of epoxide, and intramolecular [5 + 2] cycloaddition reaction as the key transformations. The stereochemistry was determined by the X-ray crystallographic analysis.
- Guo, Rui,Zhai, Hongbin,Li, Yun
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- SELECTIVE CARBOMETALLATION OF α,β-UNSATURATED CARBONYL COMPOUNDS AND SUBSTITUTED OXACYCLOPROPANES WITH ZIRCONIUM-DIENE COMPLEXES
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The reactions of zirconium-diene complexes, ZrCp2(s-cis-diene), with bifunctional electrophiles, i.e. α,β-unsaturated ketones, unsaturated esters and substituted oxacyclopropanes were investigated.Reaction of ZrCp2(s-cis-isoprene) with an equivalent of 3-buten-2-one or alkyl acrylates, selectively gives 1,2-addition products.C-C bond formation occurred at the C(1) atom of the isoprene moiety whereas 1,3-pentadiene, 2-methyl-1,3-pentadiene- and 2,4-dimethyl-1,3-pentadiene complexes induced the regioselective 1,2-addition at the C(4) position of the diene moiety.Phenyloxacyclopropane and 2-methyl-3-phenyl-oxacyclopropane also react with ZrCp2(isoprene) leading to C-C bond formation from the C(1) atom of isoprene to the oxirane carbon bearing the phenyl group.The corresponding reactions of 2-methyl-2-butene-1,4-diylmagnesium with α,β-unsaturated carbonyl compounds were also studied and found to give quite different products.
- Akita, M.,Matsuoka, K.,Asami, K.,Yasuda, H.,Nakamura, A.
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- Regioselective Monoepoxidation of 1,3-Dienes Catalysed by Transition-metal Complexes
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A procedure for regioselective monoepoxidation of mainly the less substituted double bond of 1,3-dienes with sodium hypochlorite or iodosylbenzene using various metal complexes as catalysts is presented; the results obtained are different from those found when applying the usual epoxidation reagents.
- Thomsen, Dorte S.,Schioett, Birgit,Jorgensen, Karl Anker
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- Enantioselective Radical-Polar Crossover Reactions of Indanonecarboxamides with Alkenes
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Highly efficient asymmetric intermolecular radical-polar crossover reactions were realized by combining a chiral N,N′-dioxide/NiII complex catalyst with Ag2O under mild reaction conditions. Various terminal alkenes and indanonecarboxamides/esters underwent radical addition/cyclization reactions to afford spiro-iminolactones and spirolactones with good to excellent yields (up to 99 %) and enantioselectivities (up to 97 % ee). Furthermore, a range of different radical-mediated oxidation/elimination or epoxide ring-opening products were obtained under mild reaction conditions. The Lewis acid catalysts exhibited excellent performance and precluded the strong background reaction.
- Cao, Weidi,Feng, Xiaoming,Liu, Xiaohua,Wu, Wangbin,Xu, Xi,Yu, Han,Zhang, Xiying
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supporting information
p. 4846 - 4850
(2020/02/11)
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- C5 BENZOTHIAZOLYL SULFONE COMPOUND, METHOD OF PREPARING THE SAME, METHOD OF PREPARING POLYENE DIALDEHYDE COMPOUND USING THE SAME, AND METHOD OF SYNTHESIZING LYCOPENE USING THE SAME
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Disclosed are a novel C5 benzothiazolyl sulfone compound having an acetal protecting group, a method of preparing the same, and a method of efficiently preparing an apo-carotene dialdehyde compound having a polyene dialdehyde structure using the same. Also, a method of efficiently preparing lycopene by olefination (Julia-Kocienski) between the apo-carotene dialdehyde compound (C20 crocetin dialdehyde) and C10 benzothiazolyl geranyl sulfone is provided.
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- Enantioselective total synthesis of the reported structures of (-)-9-epi-presilphiperfolan-1-ol and (-)-presilphiperfolan-1-ol: Structural confirmation and reassignment and biosynthetic insights
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When epi isn't! The first total synthesis of the reported structures of 9-epi-presilphiperfolan-1-ol and presilphiperfolan-1-ol has been achieved. Key steps are a catalytic asymmetric alkylation of a novel diene-containing electrophile followed by a two-carbon ring contraction and an intramolecular Diels-Alder cycloaddition to form the stereochemically dense tricyclic core. The synthetic work has resulted in the structural revision of presilphiperfolan-1- ol (see scheme). Copyright
- Hong, Allen Y.,Stoltz, Brian M.
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supporting information
p. 9674 - 9678
(2013/01/14)
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- Scalable synthesis of a new dihydroxylated intermediate for tetrodotoxin and its analogues
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The synthesis of a novel intermediate for tetrodotoxin and its analogues, possessing two hydroxy groups at C-8 and C-11, is described. The procedure involves a Diels-Alder reaction between bromolevoglucosenone and a tert-butyldiphenylsilyl-protected isoprenol during which the C-11 group hydroxy is installed. Subsequent transformations, including an Overman rearrangement, affords a cyclohexene intermediate containing a trichloroacetamide moiety as a requisite amino functionality for installation of the guanidine unit present in tetrodotoxin. Hydroxylation at C-8 is carried out via neighboring group participation of the trichloroacetamide to furnish the desired diol intermediate. Georg Thieme Verlag Stuttgart.
- Satake, Yoshiki,Nishikawa, Toshio,Hiramatsu, Takeshi,Araki, Hiroshi,Isobe, Minoru
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experimental part
p. 1992 - 1998
(2010/08/19)
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- Novel Intermediates, Process for Their Preparation and Process for the Preparation of Coq10 Employing the Said Novel Intermediates
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The present invention relates to an improved process for the preparation of Coenzyme Q. Coenzyme Q10 or CoQ10 has the chemical name 2-[(all-trans)-3,7,11,15,19,23,27,31,35,39-decamethyl-2,6,10,14,18,22,26,30,34,38-tetracontadecaenyl]-5,6-dimethoxy-3-methyl-1,4-benzoquinone and has the formula I. The invention also provides new intermediates useful for the preparation of CoQ10 and processes for their preparation.
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Page/Page column 14
(2008/12/08)
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- The selective epoxidation of conjugated olefins containing allylic substituents and epoxidation of propylene in the presence of butadiene
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The epoxidation of isoprene (2-methyl-1,3-butadiene) and piperylene (1,3-pentadiene), both conjugated olefins containing allylic methyl groups, has been conducted using conventional, CsCl-promoted, Ag/α-Al 2O3 catalysts. Selectivities to the allylic olefin epoxide isomers are over 20% and are much higher than expected due to the presence of the conjugated olefin structure. The epoxidation of propylene over the same catalyst under the same conditions is only 2.5%. The epoxidation of propylene in the presence of butadiene also yields PO in much higher selectivities. The presence of as little as 1% C4H6 in the reaction feedstream increases the selectivity to PO from 2.5% to over 40% at the expense of overall activity for C3H6 conversion. The upper limit of selectivity to PO in the presence of C4H6 appears to be approximately 50%, suggesting an upper limit for the effectiveness of this methodology. Epoxidation of C4H6 alone on similar Ag catalysts indicates that the consecutive reaction of EpB to CO 2/H2O is strongly limited by the presence of excess C 4H6 in the feedstream. In addition, the selectivity to EpB is directly proportional to the amount of C4H6 in the reaction feed stream. Selectivities >90% are obtained only when there is sufficient C4H6 in the reaction feedstream to control the concentration of the reactive Ag-O surface. For C4H6 epoxidation, all CO2/H2O is formed by a consecutive reaction pathway from EpB; there is no parallel pathway for the direct formation of CO2/H2O from C4H6. Using the selective epoxidation of C4H6 as the model for understanding the enhancement in selectivity for allylic olefin epoxide formation, the most likely reason for improved selectivities is that strongly adsorbed C4H6 (or other conjugated olefins) limits the ensemble size of contiguous Ag-O surface sites. These ensembles are too small for PO combustion, but not too small for PO formation.
- Monnier, John R.,Peters, Kimberly T.,Hartley, Gary W.
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p. 374 - 380
(2007/10/03)
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- Gas-phase reaction of NO3 radicals with isoprene: A kinetic and mechanistic study
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The gas-phase reaction of NO3 radicals with isoprene was investigated under flow conditions at 298 K in the pressure range 6.8 3 radicals toward isoprene was determined to be (6.86 ± 2.60) × 10-13 cm3 molecule-1 s-1. The formation of the possible oxiranes, 2-methyl-2-vinyl-oxirane and 2-(1-methyl-vinyl)-oxirane, was observed in dependence on total pressure. In the presence of O2 in the carrier gas, the product distribution was found to be strongly dependent on the reaction pathways of formed peroxy radicals, If the peroxy radicals mainly reacted in a self-reaction, the formation of organic nitrates was detected and 4-nitroxy-3-methyl-but-2-enal was identified as a main product. On the other hand, when NO was added to the gas mixture and the peroxy radicals were converted via RO2 + NO → RO + NO2, the formation of methyl vinyl ketone as the main product as well as 3-methylfuran and methacrolein was observed. From the ratio of the product yields if NO was added to the gas mixture it was concluded that the attack of NO3 radicals predominantly takes place in the 1-position. A reaction mechanism is proposed and the application of these results to the troposphere are discussed.
- Berndt, Torsten,Boege, Olaf
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p. 755 - 765
(2007/10/03)
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- Regio- and enantio-selective catalytic epoxidation of conjugated dienes
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The regio-and enantio-selective catalytic epoxidation of conjugated aliphatic dienes have been studied using a variety of achiral and chiral manganese salen complexes and sodum hypochlorite or iodosylbenzene as the terminal oxidant.The catalysts show a preference for the less substituted alkene in most of the dienes studied, and in some cases a regioselectivity of 100percent is found.The regioselectivity is dependent on the terminal oxidant applied.The enantiomeric excess (ee) obtained varies for the different conjugated dienes and the ee is generally highest for internal alkenes, where an ee of up to 71percent is observed, whereas 48percent is the highest observed ee for the less substituted alkenes.The ee is also dependent on the terminal oxidant applied.The regio- and enantio-selectivity have also been studied for different 1-(para-substituted phenyl)buta-1,3-dienes, but no regio- and enantio-selectivity dependence on the different subsituents are observed.A competitive epoxidation experiment with styrene and 1-phenylbuta-1,3-diene shows that the latter is the most reactive and the difference in reactivity is discussed on the basis of frontier orbitals of the two systems.The electronic structure of the oxo-manganese salen intermadiate is investigated using INDO/1 calculations and it is found that the triplet state is the most stable state of the intermediate.Based on the electronic structure of the oxo-maganese salen intermediate a mechanism of the oxygen transfer step to the conjugated diene is proposed.
- Rasmussen, Kaare G.,Thomsen, Dorte S.,Joergensen, Karl Anker
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p. 2009 - 2018
(2007/10/02)
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- Visible Light Induced Reactions of NO2 with Conjugated Dienes in a Low-Temperature Ar Matrix
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Visible light induced oxygen atom transfer from NO2 to conjugated dienes has been investigated in a low-temperature Ar matrix, where the dienes are 1,3-butadiene (BD), 2-methyl-1,3-butadiene (isoprene), and 2,3-dimethyl-1,3-butadiene (DMB).In each diene/NO2/Ar system, the corresponding nitrite radical, oxirane, aldehyde, and NO were obtained as the photochemical reaction products.The reactions are initiated by the formation of undetecteable short-lived oxirane biradical and NO due to visible light induced O atom transfer from NO2 to the conjugated dienes. (1) The recombination of oxirane biradicals and neighboring NO gives the nitrite radicals as the photochemical intermediate. (2) The ring closure of the biradicals leads to the formation of oxiranes. (3) The intramolecular H atom transfer of biradicals leads to the formation of aldehydes.The visible photolysis of the nitrite radicals gives rise to oxirane, aldehyde, and NO.The reaction rates are derived by measuring the absorbance changes of the products upon the 582-nm irradiation.The methyl substituent effect on the reactivity is discussed.
- Tanaka, Nobuaki,Kajii, Yoshizumi,Shibuya, Kazuhiko,Nakata, Munetaka
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p. 7048 - 7053
(2007/10/02)
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- SYNTHESIS OF α-KAINIC ACID AND α-ALLOKAINIC ACID BY Pd(0) MEDIATED OLEFIN INSERTION CARBONYLATION REACTION
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α-Kainic acid and α-allokainic acid were synthesized by Pg(0) mediated olefin insertion into allylic acetate followed by carbonylation reaction.
- Yoo, Sung-Eun,Lee, Sang-Hee,Yi, Kyu-Yang,Jeong, Nakcheol
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p. 6877 - 6880
(2007/10/02)
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- Monooxygenase-like Oxidation of Hydrocarbons by H2O2 Catalyzed by Manganese Pophyrins and Imidazole: Selection of the Best Catalytic System and Nature of the Active Oxygen Species
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Fe and Mn porphyrins alone are almost unable to catalyze cyclooctene epoxidation or cyclooctane hydroxylation by H2O2.In the presence of imidazole, Mn(III) porphyrins, and particularly Mn(TDCPP)Cl, are much better catalysts than Fe porphyrins for oxygen-atom transfer from H2O2 to hydrocarbons.From a study of various Mn porphyrin catalysts and nitrogen base cocatalysts, the most efficient system that has been selected involves Mn(TDCPP)Cl in the presence of 10 - 20 equiv of imidazole.This system leads to high yields of alkene epoxidation (90 - 100 percent in less than 1 h at room temperature).Epoxidation of 1,2-dialkylethylenes is stereospecific and corresponds to a syn addition of an oxygen atom to the double bond.This system also leads to the oxidation by H2O2 of various alkanes such as cyclohexane, cyclooctane, adamantane, ethylbenzene, or tetralin, with formation of the corresponding alcohols and ketones in yields between 40 and 80 percent.The Mn(TDCPP)Cl-imidazole-PhIO and Mn(TDCPP)Cl-imidazole-H2O2 systems exhibit the following: (i) identical stereospecificities for the epoxidation of stilbene and hex-2-ene, (ii) identical regioselectivities for the epoxidation of iosoprene and limonene as well as for the hydroxylation of n-heptane, and (iii) almost identical chemoselectivities for the oxidation of cyclohexene and of mixtures of cyclooctane and cyclooctene.This indicates that very similar, if not identical, high-valent Mn-oxo intermediates are the active oxygenating species in both systems.Thus, thanks to the presence of imidazole, it is possible to perform efficient biomimetic monooxygenations of hydrocarbons by using the Mn(TDCPP)Cl catalyst and H2O2 instead of PhIO as the oxygen-atom donor.
- Battioni, P.,Renaud, J. P..,Bartoli, J. F.,Reina-Artiles, M.,Fort, M.,Mansuy, D.
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p. 8462 - 8470
(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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- Facile synthesis of the enantiomers of frontalin
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S(-)- and R-(+)-frontalin (1,5-dimethyl-6,8-dioxabicyclooctane) were prepared from (E)-2-methyl-2,6-heptadiene-1-ol utilizing the Sharpless asymmetric epoxidation reaction to induce chirality.The six-step synthetic sequence proceeded in approximately 50percent overall yield and was found to be suitable for the preparation of multi-gram quantities of either enantiomer with >=90percentee.
- Johnston, B. D.,Oehlschlager, A. C.
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p. 2148 - 2154
(2007/10/02)
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- Preparation and photolysis of deuterium-labelled rhodopsin analogues
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The compounds 18- and 19-trideutero-11-cis-retinal, > 99percent pure, with over 98percent and 99percent trideuterium incorporation were synthesized together with the corresponding all-trans derivatives.Rhodopsins were prepared from bovine opsin and 18- and 19-trideutero-11-cis-retinal, 18- and 19-trideutero-all-trans-retinal were isolated as oximes after photolysis of the corresponding rhodopsins.The oximes showed the same deuterium incorporation as the starting 18- and 19-trideutero-11-cis-retinals and as those oximes obtained by denaturation of 18- and 19-trideuterorhodopsin in the dark.These results demonstrate that during rhodopsin photolysis no detectable exchange of D or H occurs at carbon atoms 18 and 19.These facts, together with Resonance Raman data of 18-trideutero-bathorhodopsin and 5-demethylbathorhodopsin, establish that the primary step in rhodopsin photochemistry is not a phototautomerization involving the 5-CH3 group.With respect to the possibility that the primary step is a phototautomerization involving the 9-CH3 group, the situation is less clear.At this time experimental evidence of the various research disciplines is insufficiently conclusive to establish unambiguously which of the two possibilities, cis-trans photoisomerization or phototautomerization involving the 9-CH3 group, is the primary event in visual photochemistry.
- Fransen, M. R.,Palings, I.,Lugtenburg, J.,Jansen, P. A. A.,Groenendijk, G. W. T.
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p. 384 - 391
(2007/10/02)
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