10395-53-6Relevant academic research and scientific papers
Room temperature asymmetric Pd-catalyzed methoxycarbonylation of norbornene: Highly selective catalysis and HP-NMR studies
Blanco, Carolina,Godard, Cyril,Zangrando, Ennio,Ruiz, Aurora,Claver, Carmen
experimental part, p. 6980 - 6991 (2012/07/14)
Palladium complexes bearing monodentate and bidentate phosphine ligands (1-7) were synthesised and used as catalyst precursors in the methoxycarbonylation of norbornene. The catalytic systems bearing ligands 1, 3 and 4 afforded excellent conversions (>99%) and selectivity of the ester (>99%). NMR investigations showed that using complex 1a as the precursor resulted in the protonated phosphine, 1-H+, being formed under catalytic conditions and thus the addition of acid is not required for the activation of this system since the reaction involving the precursor with methanol under CO pressure produces 2 equivalents of HCl and leads to the formation of the active species. The protonation of ligand 4 under methoxycarbonylation conditions was also observed and the diprotonated diphosphine was isolated and characterised. This compound was tested as a ligand and acid source in a catalysis and provided excellent conversion and high selectivity to the ester.
Ion-molecule complexes in 1,2 alkyl shifts
Gappa, Andrea,Herpers, Ekkehard,Herrmann, Roland,Hülsewede, Volker,Kappert, Wilhelm,Klar, Matthias,Kirmse, Wolfgang
, p. 12096 - 12106 (2007/10/03)
The internal return of neutral leaving groups was studied in rearrangements of polycyclic systems (2-norpinyl → 2-norbornyl, endo- → exo-tricyclo[5.2.1.02.6]dec-8-yl, bicyclo[3.2.0]hept-2-yl → 7-norbornyl, and 4-protoadamantyl → 2-adamantyl). Acid catalysis was applied to 18O-labeled alcohols in aqueous organic solvents, to alcohols in methanol, and to ethers R-O-R′ in alcohols R″-OH. The leaving group was found to attack the migration origin in competition with solvent molecules. Return:exchange ratios were obtained from product distributions, either directly or by kinetic simulation (in cases of partial exchange prior to rearrangement). If departure and return of the leaving group occur on the same side of the carbon framework, return:exchange ratios ranging from 1 to 11.5 were observed. Less internal return was found for bridged than for open carbocations. Migration of the departing molecule to the opposite face (exo ? endo) or to a β carbon is a minor process (return:exchange ～ 0.1), in accordance with previous reports on inverting displacements and allylic 1,3 shifts. These data are rationalized in terms of short-lived ion-molecule (ion-dipole) complexes whose collapse competes with ligand exchange.
Carbenes and the O-H bond: Bicycloalkylidenes
Kirmse, Wolfgang,Meinert, Thomas,Modarelli, David A.,Platz, Matthew S.
, p. 8918 - 8927 (2007/10/02)
Photolyses of spirobicyclic diazirines in alcohols have been investigated in order to elucidate the insertion reactions of bicycloalkylidenes with O-H bonds. The formation of ethers from norbornane-derived diazirines (16 and 30) was traced to the intervention of diazo compounds which react by way of diazonium ions. Scavenging of the diazo compounds with potent dipolarophiles led to almost exclusive formation of nortricyclenes from 2-norbornylidenes (17 and 32). In contrast, 2-bieyclo[2,1.1]hexylidene (45) was found to undergo intermolecular reactions, including addition to alkenes and C-H insertion with cycloalkanes. When alcoholic solutions of bicyclo[2.1.1]hexane-derived diazirines (41, 58, 73, and 76) were irradiated, diazo scavengers did not eliminate the formation of ethers. By means of deuterium labels or methyl groups, rearrangement and fragmentation reactions were detected that are characteristic of carbocations (ion pairs). Protonation of 2-bicyclo[2.1.1]hexylidenes by ROH is therefore implied. Laser flash photolysis studies confirmed the divergent lifetimes of 17 (0.1 ns) and 45 (50-600 ns). The reaction rate of 45 was found to increase with the acidity of the alcohols.
Photochemistry of alkyl halides. 12. Bromides vs Iodides
Kopp, Paul J.,Adkins, Rick L.
, p. 2709 - 2717 (2007/10/02)
Conditions have been developed for optimizing ionic photobehavior material balances from alkyl bromides. Hydroxide ion as an efficient for the byproduct HBr while giving minimal competing photoreduction via electron transfer to the alkyl bomide. The photobehavior of bromides 1, 11, 25, and 40 has examined and with that of the corresponding iodides 2, 12, 26, 41 under conditions. In each case, the bromide higher yields of products derived from out of cage radical intermidiates than the corresponding iodide. However, with the 2-norbornyl bromides 11 and iodides 12 showed that, of products not formed from the out of cage 2-norbornyl radical 13, the bromides 11 gave a higher percentage of products from the ionic intermediates 15 and 16 than did the iodides. Thus, electron transfer within the radical pair 14 is apparently more rapid for bromides than iodides, as expected on the of the relative electronegativities of bromine iodine. It is that the substantially higher yields of out of radical products from alkyl bromides may be due in to formation of the radical pair with greater excess energy, which results in more rapid escape from the cage. The epimeric 2-norbornyl bromides 11x and 11n underwent no detectable interconversion and afforded somewhat different product ratios. The more hindered epimer 11n underwent conversion to products at a slower than 11x. By contrast, 12x and 12n underwent substantial interconversion via out of transfer of an iodine atom from iodide 12 to radical 13. Epimerization was significantly attenuated in the more viscous solvent tert-butyl alcohol.
THE PHOTOCHEMICAL NUCLEOPHILE-OLEFIN COMBINATION, AROMATIC SUBSTITUTION REACTION (PART 2): METHANOL-CYCLIC OLEFINS, 1,4-DICYANOBENZENE
Arnold, Donald R.,Snow, Miles S.
, p. 3012 - 3026 (2007/10/02)
Direct irradiation of acetonitrile-methanol (3:1) solutions of 1,4-dicyanobenzene and the cyclic olefins, cyclohexene, 1-methylcyclohexene, norbornene, and 2-methylnorbornene, leads to formation of regio- and stereoisomers of the 1:1:1 (alcohol : olefin : aromatic) adducts.This reaction can be photosensitized by electron transfer; addition of electron donors, biphenyl or phenanthrene, to the irradiation mixture generally increases the efficiency and yield of adduct formation.The efficiency of the reaction and the ratio of isomeric adducts are also affected by the addition of salts, particularly magnesium perchlorate.All of the possible regio- and stereoisomers from cyclohexene and 1-methylcyclohexene have been identified, two from cyclohexene and four from 1-methylcyclohexene.Three of the four possible isomers from norbornene were characterized; the endo, endo isomer was not detected.There are eight possible isomers from 2-methylnorbornene; six were detected and five have been isolated and identified.The two sterically hindered isomers, those having both the 4-cyanophenyl and the methoxy groups in the endo position, and exo-3-(4-cyanophenyl)-endo-2-methoxy-exo-2-methylnorbornane, were not characterized.The structures of the products were established largely on the basis of the 1H and 13C nuclear magnetic resonance spectra.The mechanism of the reaction is discussed, with emphasis on those factors that may affect the product ratio.The most striking observation is that the reaction is regioselective when magnesium perchlorate is added to the irradiation mixture.
Solvomercuration-Demercuration. 11. Alkoxymercuration-Demercuration of Representative Alkenes in Alcohol Solvents with the Mercuric Salts Acetate, Trifluoroacetate, Nitrate, and Methanesulfonate
Brown, Herbert C.,Kurek, Joseph T.,Rei, Min-Hon,Thompson, Kerry L.
, p. 2551 - 2557 (2007/10/02)
The alkoxymercuration-demercuration of seven representative olefins with the mercuric salts acetate, trifluoroacetate, nitrate, and methanesulfonate, in methyl, ethyl, isopropyl, and tert-butyl alcohols was examined.Mercuric acetate was effective only in methanol and ethanol.On the other hand, mercuric trifluoroacetate was effective in all four solvents, giving in most cases high yields of the corresponding ethers.Both mercuric nitrate and mercuric methanesulfonate were effective in methanol, ethanol, and 2-propanol.However, in several cases poor selectivity for the ether was observed, as evidenced by the formation of significant amounts of side products.Both electronic and steric effects are important factors in the reaction.Moreover, the structure of the olefin has a pronounced effect, both on the types of oxymercurials formed and on their stability to the reaction conditions.
