20474-50-4Relevant academic research and scientific papers
Experimental and theoretical approaches to the influence of the addition of pyrene to a series of Pd and Ni NHC-based complexes: Catalytic consequences
Valds, Hugo,Poyatos, Macarena,Ujaque, Gregori,Peris, Eduardo
, p. 1578 - 1588 (2015/01/30)
A series of Ni and Pd complexes with three different N-heterocyclic carbene (NHC)-based ligands (imidazolylidene, benzimidazolylidene and pyrene-imidazolylidene) has been prepared and fully characterized. The influence of the addition of pyrene to solutions containing these complexes is studied by means of NMR and UV/Vis spectroscopies and by cyclic voltammetry. The addition of pyrene to the pyrene-NHC-containing Pd and Ni complexes gives rise to the formation of adducts by π-π stacking interactions between pyrene and the pyrene group of the NHC ligand. This interaction causes a modification of the electronic properties of the metal, as demonstrated by cyclic voltammetric studies of the Ni-NHC complexes. Theoretical calculations support this type of π-interactions, and justify the higher interactions observed with the pyrene-NHC containing complexes. The catalytic activities of the complexes were tested in the Suzuki-Miyaura C-C coupling and in the α-arylation of ketones. The addition of pyrene as an external π-stacking additive does not affect the activities of the complexes in the Suzuki-Miyaura coupling, but this observation may be justified due to the fact that the process is heterogeneously catalyzed, as indicated by the mercury-drop test. The addition of pyrene to the catalytic α-arylation of ketones results in a decrease in the activity of the reactions catalyzed by the pyrene-imidazolylidene palladium complex, whereas the other two catalysts do not modify their activity in the presence of this π-stacking additive.
Chiral bronsted acid from a cationic gold(I) complex: Catalytic enantioselective protonation of silyl enol ethers of ketones
Cheon, Cheol Hong,Kanno, Osamu,Toste, F. Dean
supporting information; experimental part, p. 13248 - 13251 (2011/10/10)
A chiral Bronsted acid has been developed from a cationic gold(I) disphosphine complex in the presence of alcoholic solvent and applied to the enantioselective protonation reaction of silyl enol ethers of ketones. Various optically active cyclic ketones were obtained in excellent yields and high enantioselectivities, including cyclic ketones bearing aliphatic substrates at the α-position. Furthermore, the application of this Bronsted acid was extended to the first Bronsted acid-catalyzed enantioselective protonation reaction of silyl enol ethers of acyclic substrates, regardless of their E/Z ratio.
New preparation of benzylic zinc reagents via a fragmentation reaction
Piazza, Claudia,Millot, Nicolas,Knochel, Paul
, p. 88 - 95 (2007/10/03)
The fragmentation of sterically hindered homobenzylic zinc alcoholates proceeds readily leading to benzylic zinc reagents free from any Wurtz-coupling product. Reaction of these organometallic intermediates with various aldehydes produces new homobenzylic
Felkin-Anh stereoselectivity in cycloadditions of acetylketene: Evidence for a concerted, pseudopericyclic pathway
Shumway,Ham,Moer,Whittlesey,Birney
, p. 7731 - 7739 (2007/10/03)
The cycloadditions of acetylketene with α-chiral aldehydes and ketones are shown to be diastereoselective, forming a tertiary or quaternary chiral center at an acetal or ketal carbon with good stereocontrol. X-ray crystallography of a minor product (5b) shows that the major products (e.g., 4b) are those predicted by the Felkin-Anh model. Transition states are reported at the MP2/6-31G* level for the addition of ethanal to formylketene and at the B3LYP/6-31G* level for the addition of 2-phenylpropanal. The ground-state conformations of the reactants and products are used to rationalize the relative energies and geometries of the transition states without the need to invoke the Cieplak hypothesis. However, chiral substituents on the α-oxoketene show no diastereoselectivity. These experimental and computational results are only consistent with the nearly planar, pseudopericyclic transition state previously proposed.
On the Reduction of Enol Acetates and Enolates derived from α-Chiral Ketones with Lithium Tetrahydridoaluminate
Orellana, Guillermo,Perez-Ossorio, Rafael,Quiroga, Maria L.,Sanchez-Asiain, Maria P.
, p. 679 - 682 (2007/10/02)
The Z- and E-isomers of 1-acetaoxy-1,2-diphenylprop-1-ene (1) and (2), and of 3-acetoxy-4,4-dimethyl-2-phenylpent-2-ene (3) and (4), have been converted into their respective alcohols (1RR,2SS)- and (1RS,2RS)-1,2-diphenylpropan-1-ol (5) and (6), and (1RR,
Synthese de tertiobutylcetones α-azotees de type =N-C(R1)(R2)-CO-C(CH3)3
Montignoul, Claude,Richard, Marie-Josee,Vigne, Christian,Giral, Louis
, p. 1509 - 1519 (2007/10/02)
The α-nitrogen-ketones 2, 3 and 4 were prepared from α-bromoketones.These were synthesized by the bromination of the ketones which had been obtained by the pinacolone or benzyltertiobutylketone alkylation from the corresponding halo-derivatives.We have observed that the bromination of the ketones depends to some extent upon the nature of these compounds.
Stereoselectivity in the Condensation Reactions of 1-Phenylethyl Alkyl and Phenyl Ketones with Organometallic Reagents
Alvarez-Ibarra, Carlos,Arjona, Odon,Perez-Ossorio, Rafael,Perez-Rubalcaba, Alfredo,Quiroga, Maria L.,Santesmases, Maria J.
, p. 1645 - 1648 (2007/10/02)
Stereochemical results of the condensation reactions of a series of ketones, PhCHMeCOR (R= Me, Et, Pri, But, Ph), with various organomagnesium and organolithium derivatives in ethers as solvents are reported.Results are accounted for on the basis of competition between two transition states which may adopt either Karabatsos- or Felkin-type conformations according to the nature of R, the reagent nucleophilicity, and the polarity of solvent.Polar and steric analysis of this reaction allows highly stereoselective syntheses of diastereoisomeric α-phenylalkanols to be devised.
