59588-12-4Relevant articles and documents
Formation of Cyclopropanes via Activation of (γ-Methoxy)alkyl Gold(I) Complexes with Lewis Acids
Kim, Nana,Widenhoefer, Ross A.
, p. 3160 - 3167 (2020/09/12)
Treatment of the gold 3-methoxy-3-phenylpropyl complex (P)AuCH2CH2CH(OMe)Ph [P = P(t-Bu)2o-biphenyl] with AlCl3 at -78 °C led to the immediate (≤5 min) formation of a 4:1 mixture of phenylcyclopropane and (1-methoxypropyl)benzene in 86 ± 5% combined yield. Lewis acid activation of the stereochemically pure isotopomer erythro-(P)AuCH2CHDCH(OMe)Ph led to the formation of cis-2-deuterio-1-phenylcyclopropane in 84 ± 5% yield as a single stereoisomer, which established that cyclopropanation occurred with inversion of the γ-stereocenter. Similarly, ionization of the stereochemically pure cyclohexyl gold complex cis-(P)AuCHCH2CH(OMe)CH2CH2CH2 at -78 °C formed bicyclo[3.1.0]hexane in 82% ± 5% yield, which validated a low energy pathway for cyclopropanation involving inversion of the α-stereocenter. Taken together, these observations are consistent with a mechanism for cyclopropane formation involving backside displacement of both the Cγleaving group and the Cα (L)Au+ fragment via a W-shaped transition state.
Peroxometalates immobilized on magnetically recoverable catalysts for epoxidation
Qiao, Yunxiang,Li, Huan,Hua, Li,Orzechowski, Lars,Yan, Kai,Feng, Bo,Pan, Zhenyan,Theyssen, Nils,Leitner, Walter,Hou, Zhenshan
, p. 1128 - 1138 (2013/03/13)
Magnetically separable catalysts were prepared and employed for the epoxidation of olefins with hydrogen peroxide. In all cases the magnetic core was firstly covered with a silica layer to prevent iron ion-initiated decomposition of hydrogen peroxide. The catalytic active species, an ionic liquid-type peroxotungstate, was then immobilized either by hydrogen bonding (catalyst 1) or by covalent SiO linkage (catalyst 2). In addition to a thorough characterization by FT-IR, XRD, NMR, DRIFT, XPS, and TEM, the catalytic potential was evaluated in the epoxidation of a variety of olefins as well as allylic alcohols. Both catalysts showed essentially a constant activity after at least ten consecutive cycles. On the basis of the research above, a new type of magnetically separable catalyst was constructed by immobilization of lacunary-type phosphotungstate by hydrogen bonding between the sulfonate anion and silanol group on the surface of the core-shell magnetic nanoparticles. After the detailed characterization, the catalyst was used in the epoxidation of a variety of olefins and allylic alcohols and was found to possess high activity, selectivity towards epoxides, and a constant activity after at least ten catalytic recycles without solvent.
Wagner-Meerwein rearrangements in the gas phase: Anchimeric assistance to acid-induced dissociation of optically active phenylpropanols
Speranza, Maurizio,Filippi, Antonello
, p. 834 - 844 (2007/10/03)
The kinetics and the stereochemistry of Wagner-Meerwein rearrangements of O-protonated and O-methylated (S)-1-phenyl-2-propanol (1s(A)+; A=H or Me) and (S)-2-phenyl-1-propanol (2S(A)+; A=H or Me) have been investigated in the gas phase at 750 Torr and in the 25-140°C temperature range. The 1S(A) and 2S(A)+ intermediates were generated in the gas phase by reaction of the C(n)H5+(n=1, 2; A= H) and (CH3)2F+ ions (A - Me), formed by stationary γ radiolysis of bulk CH4 and CH3F, respectively, with the corresponding optically active alcohols. The results are consistent with unimolecular H2O loss from both 1s(H)+ and 2s(H); this is anchimerically assisted by all the groups adjacent to the leaving moiety. Anchimeric assistance appears much less efficient in both 1S(Me)+ and 2S(Me)+. Analysis of the activation parameters indicates that competing neighboring-group participation in C-O bond fission in 1s(H)+ and 2s(H) respond essentially to entropic rather than enthalpic factors. The stereochemical distribution of the reaction products allowed us to discern between backside and frontside phenyl-group participation in 1s(H+). The counterintuitive observation of a frontside Ph participation, with an activation energy 1.3±0.5 kcal mol-1 lower than that of the accompanying backside assistance, is attributed to conformational factors and to the stabilizing electrostatic interactions between the phenonium ion and the leaving H2O complex that is spatially allowed only in the frontside participation and forbidden in the backside one.
