620987-93-1Relevant academic research and scientific papers
An examination of VANOL, VAPOL, and VAPOL derivatives as ligands for asymmetric catalytic Diels-Alder reactions
Heller, Douglas P.,Goldberg, Daniel R.,Wu, Hongqiao,Wulff, William D.
, p. 1487 - 1503 (2007/10/03)
Several derivatives of the vaulted biaryl ligand VAPOL were prepared and evaluated as chiral ligands for aluminum Lewis acids in the catalytic asymmetric Diels-Alder reactions of methyl acrylate and methacrolein with cyclopentadiene. The substituents on VAPOL were introduced into the 6- and 6′-positions in an effort to further extend the chiral pocket of the major groove, which contains the phenol functions at the 4- and 4′-positions. The set of four new ligands that have been prepared have the following groups introduced into the 6- and 6′-positions of VAPOL: bromide, methyl, phenyl and 3,5-di-t-butylphenyl. All of these ligands give lower asymmetric inductions than the unsubstituted VAPOL for the Diels-Alder reactions of both methyl acrylate and methacrolein. The positive cooperativity of added carbonyl compounds on the autoinduction in the Diels-Alder reaction of methyl acrylate and cyclopentadiene were also investigated with the VANOL and VAPOL ligands as well as the 6,6′-dibromo and 6,6′-diphenyl derivatives of VAPOL. Only the reaction with VAPOL showed any significant positive cooperativity. The reaction with VANOL was sluggish at -78°C, but at higher temperatures, the reaction did exhibit positive cooperativity that was similar to that of VAPOL. Finally, no positive cooperativity was observed with the VAPOL ligand for the reaction of methacrolein and cyclopentadiene.
Bridged bi-aromatic ligands, catalysts, processes for polymerizing and polymers therefrom
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Page 40, (2010/02/05)
New ligands and compositions with bridged bis-aromatic ligands are disclosed that catalyze the polymerization of monomers into polymers. These catalysts with metal centers have high performance characteristics, including higher comonomer incorporation int
From mutagenic to non-mutagenic nitroarenes: Effect of bulky alkyl substituents on the mutagenic activity of nitroaromatics in Salmonella typhimurium. Part II. Substituents far away from the nitro group
Klein, Markus,Erdinger, Lothar,Boche, Gernot
, p. 69 - 82 (2007/10/03)
Derivatives of 4-nitrobiphenyl, 4-nitrosobiphenyl, 2-phenyl-5-nitropyridine (2-aza-4-nitrobiphenyl) and 2-nitrofluorene, bearing various alkyl substituents far away from the nitro group (4'-position in nitrobiphenyls, 7-position in 2-nitrofluorenes) were synthesised and tested for mutagenic potency in strains TA98 and TA100 of Salmonella typhimurium. In the absence of S9 in both strains, mutagenicity of all compounds decreased with increasing steric demand of the attached alkyl groups as, e.g., for the 4-nitrobiphenyl series in the order 4'-H>4'-Me>4'-Et>4'-nBu>4'-iPr>4'-tBu>4'-Ad (Ad=adamantyl). Changes of the molecular shape from 'planar' to non-planar caused by the bulk of the introduced substituents (without influencing the twisting of the nitro substituent or the phenyl rings in the biphenyl compounds) may be responsible for this effect by interfering with an efficient intercalation into DNA.A comparison between experimental and theoretical values as calculated from recently developed equations (QSAR) confirmed our previous results (see the preceding paper) that mutagenicity of alkyl-substituted nitroaromatics cannot be predicted by hydrophobicity and LUMO-energies alone without including steric parameters. Copyright (C) 2000 Elsevier Science B.V.
