16914-16-2Relevant academic research and scientific papers
Solid-state deuterium nuclear magnetic resonance of the methyl dynamics of poly(α-methylstyrene) and polymethylphenylsilane
O'Connor, Robert D.,Ginsburg, Eric J.,Blum, Frank D.
, p. 7247 - 7259 (2000)
The methyl-d3 dynamics of two relatively similar polymers, poly(α-methylstyrene) (PAMS-d3) and polymethylphenylsilane (PMPS-d3), are investigated via deuterium NMR relaxation experiments. Our analysis of the relaxation data uses the entire solid-echo spectra to maximize the precision of the experiments with regard to the information available on the methyl dynamics. The analysis is novel in that it does not use Mx or M0 to fit the relaxation data. Additionally, the three-site symmetric jump model is shown to not have an observable azimuthal angular dependence for T1 relaxation. The methyl dynamics are quantified with τm, σ, and f which are the log-average correlation time, half-height full-width (base 10) of a log-normal distribution of reorientation rates, and the anisotropy of the relaxation, respectively. The anisotropy parameter, f, is based on a serial combination of the rotational diffusion and symmetric three-site jump reorientation of a methyl deuteron. This serial model coupled with a distribution of τc's has a minimal number of parameters that have physical meaning and quantify the observations of our relaxation data. Generally, at similar temperatures the methyl reorientation in PAMS-d3 is at least 100 times slower than that of PMPS-d3. For both polymers, both τm and a decrease with increasing temperature, resulting in activation energies of 12 and 5 kJ/mol for PAMS-d3 and PMPS-d3, respectively. Also, with increasing temperature a mechanistic change from three-site jump to rotational diffusion is observed and quantified. This information, along with that of other studies, suggests that the PAMS-d3 methyls have highly restrictive environments that may be closely coupled to phenyl-ring reorientation.
Cyclometalated Iridium-PhanePhos Complexes Are Active Catalysts in Enantioselective Allene-Fluoral Reductive Coupling and Related Alcohol-Mediated Carbonyl Additions That Form Acyclic Quaternary Carbon Stereocenters
Schwartz, Leyah A.,Holmes, Michael,Brito, Gilmar A.,Gon?alves, Théo P.,Richardson, Jeffery,Ruble, J. Craig,Huang, Kuo-Wei,Krische, Michael J.
supporting information, p. 2087 - 2096 (2019/02/05)
Iridium complexes modified by the chiral phosphine ligand PhanePhos catalyze the 2-propanol-mediated reductive coupling of diverse 1,1-disubstituted allenes 1a-1u with fluoral hydrate 2a to form CF3-substituted secondary alcohols 3a-3u that incorporate acyclic quaternary carbon-containing stereodiads. By exploiting concentration-dependent stereoselectivity effects related to the interconversion of kinetic (Z)- and thermodynamic (E)-σ-allyliridium isomers, adducts 3a-3u are formed with complete levels of branched regioselectivity and high levels of anti-diastereo- and enantioselectivity. The utility of this method for construction of CF3-oxetanes and CF3-azetidines is illustrated by the formation of 4a and 6a, respectively. Studies of the reaction mechanism aimed at illuminating the singular effectiveness of PhanePhos as a supporting ligand in this and related transformations have led to the identification of a chromatographically stable cyclometalated iridium-(R)-PhanePhos complex, Ir-PP-I, that is catalytically competent for allene-fluoral reductive coupling and previously reported transfer hydrogenative C-C couplings of dienes or CF3-allenes with methanol. Deuterium labeling studies, reaction progress kinetic analysis (RPKA) and computational studies corroborate a catalytic mechanism involving rapid allene hydrometalation followed by turnover-limiting carbonyl addition. A computationally determined stereochemical model shows that the ortho-CH2 group of the cyclometalated iridium-PhanePhos complex plays a key role in directing diastereo- and enantioselectivity. The collective data provide key insights into the structural-interactional features of allyliridium complexes required to enforce nucleophilic character, which should inform the design of related cyclometalated catalysts for umpoled allylation.
Chelation versus Non-Chelation Control in the Stereoselective Alkenyl sp2 C?H Bond Functionalization Reaction
Liang, Qiu-Ju,Yang, Chao,Meng, Fei-Fan,Jiang, Bing,Xu, Yun-He,Loh, Teck-Peng
supporting information, p. 5091 - 5095 (2017/04/24)
A hydroxy group chelation-assisted stereospecific oxidative cross-coupling reaction between alkenes was developed under mild reaction conditions. In the presence of palladium catalyst, the alkenes tethered with hydroxy functionality can couple efficiently with electron-deficient alkenes to form the corresponding multi-substituted olefin products. The hydroxy group on the substrate could play dual roles in reaction, acting as the directing group for alkenyl C?H bond activation and controlling the stereoselectivity of the products.
Iron-catalyzed olefin hydrogenation at 1 bar H2 with a FeCl3-LiAlH4 catalyst
Gieshoff, Tim N.,Villa, Matteo,Welther, Alice,Plois, Markus,Chakraborty, Uttam,Wolf, Robert,Jacobi Von Wangelin, Axel
supporting information, p. 1408 - 1413 (2015/03/18)
The scope and mechanism of a practical protocol for the iron-catalyzed hydrogenation of alkenes and alkynes at 1 bar H2 pressure were studied. The catalyst is formed from cheap chemicals (5 mol% FeCl3-LiAlH4, THF). A homogeneous mechanism operates at early stages of the reaction while active nanoparticles form upon ageing of the catalyst solution. This journal is
Diastereo- and enantioselective Aza-MBH-type reaction of nitroalkenes to N-tosylimines catalyzed by bifunctional organocatalysts
Wang, Xiao,Chen, Yong-Fei,Niu, Liang-Feng,Xu, Peng-Fei
supporting information; body text, p. 3310 - 3313 (2009/12/05)
The first example of diastereo- and enantioselective aza-MBH-type reaction was accomplished by the asymmetric synthesis of β-nitro-γenamines via a (1R,2R)-diaminocyclohexane thiourea derivative mediated tandem Michael addition and aza-Henry reaction in good yields (up to 95%) and high enantioselectivities (up to 91% ee) and diastereoselectivities (up to 1:99 dr).
Ruthenium-assisted synthesis of gem-deuterated alkenes from monosubstituted propargyl alcohols and D2O
Bianchini, Claudio,De los Rios, Isaac,Lopez, Carlos,Peruzzini, Maurizio,Romerosa, Antonio
, p. 485 - 488 (2007/10/03)
The cyclohexenylvinylidene complex fac,cis-[(PNP)RuCl2{C=CH(C=CHCH2CH2CH2CH2)}] (2) is synthesized by reaction of mer,trans-[(PNP)RuCl2(PPh3)] (1) with 1-ethynylcyclohexanol [PNP
Organic Reactions of Sulfur Dioxide. Reactions with Nucleophilic Duoble Bonds Leading to the Isomerization, Aromatization, Selective Hydrogen-Deuterium Exchange, and Electron-Transfer Processes
Masilamani, Divakar,Manahan, Edward H.,Vitrone, John,Rogic, Milorad M.
, p. 4918 - 4931 (2007/10/02)
Sulfur dioxide reacts readily with 1-alkoxycyclohexenes to give unstable 1,2,3,4,5a,6,7,8,9,9b-decahydro-4a,9a-dialkoxydibenzothiophene 5,5-dioxides, which, after elimination of alcohol, afford crystalline 1,2,3,4,5a,6,7,8,9-nonahydro-4a-alkoxydibenzothiophene 5,5-dioxides.These tricyclic sulfones undergo sulfur dioxide extrusion to give a 1:1 mixture of 2- and 6-cyclohex-1-enyl-1-alkoxy-1-cyclohexenes.This mixture of the 1,3- and 1,4-dienes reacts quantitatively with sulfur dioxide to give back the starting tricyclic sulfones.The apparent isomerization of the 1,4-diene to 1,3-isomer is an example of a quite general isomerization of a wide variety of olefins in sulfur dioxide.It appears that these reactions involve the allylic sulfinic acids as transient intermediates, which are capable of a very facile 1,3-thiaallylic rearrangement.When the reactions of those olefins that do undergo isomerization in liquid sulfur dioxide are carried out in the presence of deuterium oxide, a highly stereospecific hydrogen-deuterium exchange is observed.For example, optically active 1-methyl-4-isopropyl-cyclohexene affords 6,6-dideuterio-1-(trideuteroimethyl)-4-isopropylcyclohexene without appreciable racemization. 1,4-Cyclohexadienes react with liquid sulfur dioxide at room temperature to give quantitatively the aromatic hydrocarbon, elemental sulfur, and water. 1,4-Disubstituted 1,3-cyclohexadienes, on the other hand, under similar conditions provide only a small amount of the aromatic hydrocarbon, the main product being a polymeric hydrocarbon(s).Surprisingly, 1-methyl-4-isopropyl-1,3-cyclohexadiene in the presence of oxygen provided 1-methyl-4-isopropylbenzene exclusively.This reaction involves ascaridole as the intermediate, which then reacts with sulfur dioxide to give the aromatic hydrocarbon and sulfuric acid.When the reaction with oxygen is conducted at a low temperature, the ascaridole can be obtained in a quantitative yield.The mechanisms of olefin isomerization, hydrogen-deuterium exchange, and aromatization of cyclohexadienes are discussed.
Photochemistry of Some Deoxybenzoins in Micellar Solutions. Cage Effects, Isotope Effects, and Magnetic Field Effects
Turro, Nicholas J.,Mattay, Jochen
, p. 4200 - 4204 (2007/10/02)
The photolyses of 1,2-diphenyl-2-methyl-1-propanone (1) and its D-, 13C-, and alkyl-substituted derivatives 2-5 in various micellar solutions have been investigated.It was found that the extent of cage disproportionation to yield benzaldehydes 6 and α-methylstyrenes 7 is enhanced by a factor of about 10 compared to the photolyses in homogeneous organic solvents.The advantage of using micelles rather than homogeneous solutions to enhance the magnitude of magnetic isotope and magnetic field effects on cage disproportionation is demonstrated.The results are interpreted in terms of a mechanism involving the competition between hyperfine-induced intersystem crossing of a triplet radical pair (3RP) to form a singlet radical pair (1RP) and escape of 3RP from the micelle.
