29430-01-1Relevant academic research and scientific papers
Synthesis of trithiolanes and tetrathianes from thiiranes catalyzed by ruthenium salen nitrosyl complexes
Sauve, Anthony A.,Groves, John T.
, p. 4770 - 4778 (2007/10/03)
The compound [Ru(salen)(NO)(H2O)](SbF6) (1) (salen = N, N′-ethylene-bis-salicylidene aminate) reacts catalytically with thiiranes and converts them to olefins and 1,2,3,4-tetrathianes or 1,2,3-trithiolanes. The monosubstituted thiiranes styrene sulfide and propylene sulfide reacted to form the corresponding olefin and the 4-substituted 1,2,3-trithiolane in a 2:1 ratio in isolated yields in excess of 90%. The disubstituted thiirane cis-stilbene sulfide was converted to cis-stilbene and 5,6-trans-1,2,3,4-diphenyltetrathiane in a 3:1 ratio in the presence of a catalytic amount of 1 in CD3NO2. Coordination of cis-stilbene sulfide to the salen complex in a ligand substitution reaction was established by isolation of [Ru(salen)(NO)(cis-stilbene sulfide)]-(SbF6) (6). 1H NMR studies performed on 6 indicated that the salen macrocycle had rearranged upon thiirane coordination. A similar rearrangement was found to be stabilized by other ligands including tetramethylethylene sulfide, tetrahydrothiophene, and d3-acetonitrile. The α-deuterio-cis-stilbene sulfide catalyst adduct (d-6) reacted with unlabeled cis-stilbene sulfide to form deuterium-labeled trans-diphenyl-tetrathiane and unlabeled cis-stilbene as shown by GCMS and 1H NMR. Thus, the solution thiirane behaves as a sulfur donor and forms olefin, whereas the coordinated thiirane becomes the cyclic polysulfide. β-cis-Deuteriostyrene sulfide was used to show that ring closure to form cyclic polysulfide incorporated inversion of stereochemistry versus starting thiirane. A mechanism for catalysis consistent with experimental data is presented that requires coordination of thiirane to the metal complex followed by bimolecular attack of free thiirane on the coordinated thiirane.
Ruthenium meso-tetrakis(2,6-dichlorophenyl)porphyrin complex immobilized in mesoporous MCM-41 as a heterogeneous catalyst for selective alkene epoxidations
Liu, Chun-Jing,Yu, Wing-Yiu,Li, Shou-Gui,Che, Chi-Ming
, p. 7364 - 7369 (2007/10/03)
A ruthenium complex of meso-tetrakis(2,6-dichlorophenyl)porphyrin, [RuII(TDCPP)(CO)(EtOH)], is immobilized into mesoporous MCM-41 molecular sieves; the supported Ru catalyst can effect highly selective heterogeneous alkene epoxidations using 2,6-dichloropyridine TV-oxide as terminal oxidant. Aromatic and aliphatic alkenes can be efficiently converted to their epoxides in good yields and selectivities, and cis-alkenes such as czs-stilbene, cis-β-methylstyrene, and cis-β-deuteriostyrene are epoxidized stereospecifically. Oxidation of cycloalkenes, e.g., norbornene and cyclooctene, can be carried out effectively using the heterogeneous Ru-catalyzed reaction while these alkenes are unreactive in the zeolite-based titanium silicate (TS-l)-catalyzed conditions (Murugavel, R.; Roesky, H. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 477). On the other hand, the Ru/M-41(m) catalyst displays size selectivity in the (+)-limonene oxidation where the terminal C=C bond (vs internal trisubstituted C=C bond) becomes more readily oxidized. Bulky 3,4,6-tri-O-benzyl-D-glucal has failed to react under the heterogeneous Ru-catalyzed conditions, whereas the smaller acetyl derivative is converted to a 3:1 mixture of α- and β-glycal epoxides. The Ru/M-41(m) catalyst can be used repeatedly, and 67% of its initial activity is retained after 11 691 turnovers (three runs). The loss of activity is attributed to catalyst leaching and/or deactivation. On the basis of Hammett correlation (ρ+ = -0.72, R = 0.997) and product studies (cyclohexene and crs-alkenes as the substrates), a reactive dioxorutheniumCVI) porphyrin intermediate is not favored. An oxoruthenium(V) complex or oxoruthenium(IV) porphyrin cation radical could be the key intermediate for this highly selective epoxidation reaction.
Zinc(II)-catalysed transformation of epoxides to aziridines
Kuehnau, Dorte,Thomsen, Ib,Jorgensen, Karl Anker
, p. 1167 - 1170 (2007/10/03)
The Lewis acid-catalysed transformation of epoxides to aziridines with iminophosphoranes as the nitrogen-fragment donor has been investigated. Of the Lewis acids tested, zinc(II) complexes had the best catalytic properties. The method works best for terminal and cyclic epoxides, internal epoxides being less reactive. Of the various iminophosphoranes employed N-(triphenylphosphoranylidene)-aniline and -isopropylamine were the most successful. The zinc(II)-catalysed reaction has been studied for chiral styrene oxides for which the enantiomeric excess of the aziridine produced is dependent on the reaction time. The reaction of achiral and chiral styrene oxides and N-(triphenylphosphoranylidene)aniline in the presence of a zinc(II) complex having a chiral ligand has been investigated as has the reaction for cis-deuteriostyrene oxide in order to obtain information about the stereochemical outcome of the reaction. A mechanism for the title reaction is discussed on the basis of the experimental results.
DIASTEREOTOPIC SELECTION OF C2 HYDROGENS IN THE REARRANGEMENT OF C1-SUBSTITUTED EPOXIDES: AN EXAMINATION OF STYRENE OXIDE
Coxon, J. M.,McDonald, D. Q.
, p. 2575 - 2576 (2007/10/02)
Rearrangement of styrene oxide with (a) LiClO4 and (b) BF3 to give phenylethanal exhibits diastereotopic selection with migration of the hydrogen trans to the phenyl group being favoured 1.4 and 1.14 times respectively.The rate of rotation about the C1-C2
Oxygenation of Styrene by Cytochrome P-450 Model Systems: A Mechanistic Study
Collman, James P.,Kodadek, Thomas,Brauman, John I.
, p. 2588 - 2594 (2007/10/02)
The manganese and iron porphyrin catalyzed oxygenation of styrene results in the production of phenylacetaldehyde as well as the expected epoxide.It is demonstrated that aldehyde is a primary product and dose not result from isomerization of styrene oxide.Isotope labeling studies show that one of the β hydrogen atoms of styrene migrates to the benzylic carbon in the course of aldehyde formation.Experiments using cis and trans deuterated styrenes reveal that there is a stereoelectronic preference for migration of the hydrogen cis to the aromatic ring.Styrene, styrene-d8, and cis-β-deuteriostyrene yield similar ratios of epoxide to aldehyde, indicating that β hydrogen migration occurs after the rate-determining step for formation of phenylacetaldehyde.The mechanism of this rearrangement is discussed.Some new information concerning the mechanism of olefin epoxidation by these catalysts is also presented.These results may have relevance to the mechanism of alkene oxygenation by the cytochrome P-450 monooxygenase enzymes.
Interproton Coupling Constant Variations in 3-Membered Ring Heterocycles. Separation of Lone Pair and Inductive Effects
Crist, DeLanson R.,Borsetti, Arnold P.,Jordan, Guy J.,Hammer, Charles F.
, p. 45 - 51 (2007/10/02)
In order to separate inductive and lone pair effects on geminal vicinal coupling constants in a stereochemically well-defined system, the 1H NMR spectra of phenylcyclopropane (1), N-methyl-2-phenylaziridine (2), styrene oxide (3) and 1,1-dimethyl-2-phenyl
