112246-67-0Relevant academic research and scientific papers
E-Selective Semi-Hydrogenation of Alkynes by Heterobimetallic Catalysis
Karunananda, Malkanthi K.,Mankad, Neal P.
, p. 14598 - 14601 (2015)
A unique cooperative H2 activation reaction by heterobimetallic (NHC)M′-MCp(CO)2 complexes (NHC = N-heterocyclic carbene, M′ = Cu or Ag, M = Fe or Ru) has been leveraged to develop a catalytic alkyne semi-hydrogenation transformation. The optimal Ag-Ru catalyst gives high selectivity for converting alkynes to E-alkenes, a rare selectivity mode for reduction reactions with H2. The transformation is tolerant of many reducible functional groups. Computational analysis of H2 activation thermodynamics guided rational catalyst development. Bimetallic alkyne hydrogenation and alkene isomerization mechanisms are proposed.
Aqueous Wittig reactions of aldehydes with in situ formed semistabilized phosphorus ylides
Wu, Jinlong,Zhang, Da
, p. 2543 - 2551 (2005)
The Wittig reactions of three semistabilized phosphorus ylides generated in situ from the corresponding phosphonium salts with aldehydes in water without any organic cosolvent were investigated. Most of the olefination reactions completed within between 5 min and 4.5 h in refluxing water containing 1.5 equiv of LiOH and 1.4M LiCl to afford the products in 65-100% yields. The E:Z selectivity depended not only on the substituent attached to the benzene ring of the ylides but also on the substituent bound to the aromatic aldehydes. LiCl promotes the aqueous Wittig reactions and suppresses decomposition of the ylide or the corresponding phosphonium salt. Copyright Taylor & Francis, Inc.
Novel phenylpropanoids and lignans from Illicium verum
Sy, Lai-King,Brown, Geoffrey D.
, p. 987 - 992 (1998)
Nine new phenylpropanoids (2-7, 10, 12, and 14) and two compounds representing novel structural classes of 7-O-8' and 7-O-8'.8-O-7' lignans (8 and 9, respectively) have been isolated from Illicium verum and their structures established by two-dimensional NMR. Most of these compounds appear to be biogenetically derived from threo-anethole glycol: relative stereochemistries for some members of this series were established by NOESY; absolute stereochemistries of others were determined by formation of Mosher esters.
Evidence for Dynamical Solvent Effects on the Photoisomerization of 4,4'-Dimethoxystilbene
Zeglinski, D. M.,Waldeck, D. H.
, p. 692 - 701 (1988)
The photoisomerization dynamics of 4,4'-dimethoxystilbene have been studied in n-alkanes and n-alkyl alcohols as a function of temperature at ambient pressure.By comparison with unsubstituted stilbene results the influence of the methoxy group, both intramolecular and intermolecular, on the isomerization process has been evaluated.The studies in n-alkane solvents reveal larger barrier heights and a weaker viscosity dependence for dimethoxystilbene compared to those of stilbene.This observation is in agreement with earlier ideas concerning frequency-dependent solvent effects but contrary to free volume models of solute-solvent friction.The studies in n-alkyl alcohol solvents demonstrate the inability of separating intramolecular from intermolecular effects.The potential energy surface associated with the reaction is strongly coupled with solvent dynamics, hence time dependent.These results demonstrate the importance of understanding microscopic friction and dielectric interactions on ultrashort time scales.
A simple access to biologically important trans-stilbenes via Ru-catalyzed cross metathesis
Velder, Janna,Ritter, Stefanie,Lex, Johann,Schmalz, Hans-Guenther
, p. 273 - 278 (2006)
The cross metathesis of methoxy- or acetoxy-substituted styrenes using the Grubbs II catalyst affords unsymmetrical (mixed) E-stilbenes with astonishingly high selectivity (up to 79% yield). This approach offers a short and flexible synthesis of variously substituted stilbenes, which are derivatives or precursors of biologically important compounds such as resveratrol, piceatannol, and pinostilbene. Georg Thieme Verlag Stuttgart.
TRANSFORMATIONS OF 4,4'-DIMETHOXYSTILBENE IN EARLY STAGES OF OXIDATION
Todres, Z. V.,Ionina, E. A.
, p. 962 - 964 (1992)
4,4'-Dimethoxystilbene forms a dimer as a result of one-electron anodic oxidation and undergoes cis/trans-isomerization when bound in a charge-transfer complex (chloranil as acceptor). Keywords: 4,4'-dimethoxystilbene, chloranil, charge-transfer complex, cis/trans-isomerization.
The modulation of face-face π-π Interactions in Lewis acid catalysis
Harris, Lisa D.,Jenkins, Robert L.,Tomkinson, Nicholas C.O.
, p. 1627 - 1629 (2005)
The enantiomeric excess observed for the exo-adduct from the Lewis acid catalysed Diels-Alder reaction between cyclopentadiene and methacrolein can be increased up to 21% by simple modification of the electronics of the aromatic ring in a series of stilbene-derived diol ligands, suggesting that the proposed face-face π-π interaction between the catalyst and the dienophile can be modulated by altering the electron density on the aromatic ring.
Synthesis of mono- and disubstituted sulfines via β-elimination of chloroform from trichloromethyl sulfoxides
Braverman, Samuel,Grinstein, Dan,Gottlieb, Hugo E.
, p. 13933 - 13944 (1997)
A new method for the synthesis of thioaldehyde and thioketone S-oxides by an unusual base-induced β-elimination of chloroform from readily available allylic and benzylic trichloromethyl sulfoxides is described. The reaction proceeds smoothly under mild conditions. The facile preparation of α,β-unsaturated sulfines by the new method is of special interest. A possible mechanism for this remarkable sulfine synthesis and apparently unprecedented β-elimination of chloroform is presented.
Photoisomerization and fluorescence properties of para-substituted benzyl ether-type stilbene dendrimers
Watanabe, Shinko,Ikegami, Masashi,Nagahata, Ritsuko,Arai, Tatsuo
, p. 586 - 588 (2007)
Stilbene dendrimers were prepared by coupling 4,4′-dihydroxystilbene with first, second, third, or fouth generation benzyl ether-type dendrons. Despite a short lifetime of the core structure (1 ns), all the generations of stilbene dendrimers underwent photoisomerization with the same efficiency as that of 4,4′-dimethoxystilbene.
Overcoming Catalyst Decomposition in Acrylate Metathesis: Polyphenol Resins as Enabling Agents for PCy3-Stabilized Metathesis Catalysts
Santos, Alexandra G.,Bailey, Gwendolyn A.,Dos Santos, Eduardo N.,Fogg, Deryn E.
, p. 3181 - 3189 (2017)
Phosphine-stabilized metathesis catalysts are among the most popular and widely used catalysts in organic synthesis. The second-generation Grubbs catalyst GII, in particular, dominates synthetic applications of olefin metathesis. This is commonly true even for reactions that are fundamentally incompatible with free PCy3, which is released upon entry of GII into the catalytic cycle. A leading example is cross-metathesis with electron-deficient olefins such as acrylates, for which yields are seriously degraded by a deleterious side reaction involving attack of free PCy3 on the acrylate olefin, and production of an enolate anion that decomposes the active catalyst. Here we describe a simple, powerful means of upgrading the performance of GII and its indenylidene analogue M2 to levels matching or exceeding that of the important, but more costly, phosphine-free Hoveyda catalyst HII. Key to this improvement is carrying out the reaction in the presence of a phenol-functionalized polymer resin. We demonstrate that, at standard catalyst loadings (which correspond to low concentrations of PCy3), the beneficial effect of phenol arises not from protonation of PCy3 itself, but from protonation of the enolate, thereby converting this aggressive base into an innocuous phosphonium salt. The methodology is showcased in the demanding cross-metathesis of the renewable phenylpropanoid trans-anethole with 2-ethylhexyl acrylate (an efficient route to the high-value antioxidant octylmethoxycinnamate, an active ingredient in sunscreen formulations with the tradename Octinoxate), as well as methyl acrylate, a ubiquitous and more sterically accessible coupling partner. Experiments with water-saturated toluene indicate that water cannot be substituted for the resin as a sacrificial proton donor, such treatment resulting in drastically reduced productivity. Control experiments involving macrocyclization indicate that the resin has an additional protective function beyond enolate quenching, potentially due to hydrogen bonding of polar contaminants present as impurities in the reagents or reaction medium.
