Showing items related by title, author, creator and subject.

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  1,4‐Addition of TMSCCl3 to nitroalkenes: efficient reaction conditions and mechanistic understanding

  Wu, Na (Anna); Wahl, B.; Woodward, S.; Lewis, W. (2014-06)

  Improved synthetic conditions allow preparation of TMSCCl3 in good yield (70 %) and excellent purity. Compounds of the type NBu4X [X=Ph3SiF2 (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4‐additions to a range of cyclic and acyclic nitroalkenes, in THF at 0–25 °C, typically in moderate to excellent yields (37–95 %). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies (1H, 19F, 13C and 29Si) under anaerobic conditions indicate that addition of TMSCCl3 to TBAT (both 0.13 M ) at −20 °C, in the absence of nitroalkene, leads immediately to mixtures of Me3SiF, Ph3SiF and NBu4CCl3. The latter is stable to at least 0 °C and does not add nitroalkene from −20 to 0 °C, even after extended periods. Nitroalkene, in the presence of TMSCCl3 (both 0.13 M at −20 °C), when treated with TBAT, leads to immediate formation of the 1,4‐addition product, suggesting the reaction proceeds via a transient [Me3Si(alkene)CCl3] species, in which (alkene) indicates an Si⋅⋅⋅O coordinated nitroalkene. The anaerobic catalytic chain is propagated through the kinetic nitronate anion resulting from 1,4 CCl3− addition to the nitroalkene. This is demonstrated by the fact that isolated NBu4[CH2=NO2] is an efficient promoter. Use of H2C=CH(CH2)2CH=CHNO2 in air affords radical‐derived bicyclic products arising from aerobic oxidation.
• Structural studies of titanium(IV) picolinamide alkoxide and oxide derivatives

  Lord, Rianne M.; Lord, S.M.; Pask, C.M.; McGowan, P.C. (2016)

  Reactions have been carried out using the titanium(IV) precursors TiCl4 and Ti(OiPr)4, with addition of two equivalents of a functionalized picolinamide ligand. The reactions with TiCl4 led to the formation of either a mononuclear titanium species, [Ti(N,O)Cl2X2] or a dinuclear titanium species [Ti(N,O)X3]2[l- O] (X = OMe or Cl), with incorporation of one picolinamide ligand. The ligand is bound to the titanium centre as the protonated amide. The reactions with Ti(OiPr)4 resulted in the formation of mononuclear titanium bis-picolinamide species [Ti(N,O)2(OiPr)2], and also dinuclear and trinuclear products, [(N,O)Ti (OiPr)2][l-OiPr]2 and [(N,O)Ti(OiPr)2]2[l-OiPr]2[(OiPr)2Ti][l3-O] respectively. In these cases the picolinamide ligand was found to be deprotonated and bound to the titanium as the iminolate. These molecules have been characterized by X-ray crystallographic analysis and structural characteristics are discussed.
• Biocatalytic Amide Condensation and Gelation Controlled by Light

  Sahoo, J.K.; Nalluri, S.K.M.; Javid, Nadeem; Webb, H.; Ulijn, R.V. (2014-03-25)

  We report on a supramolecular self-assembly system that displays coupled light switching, biocatalytic condensation/hydrolysis and gelation. The equilibrium state of this system can be regulated by light, favouring in situ formation, by protease catalysed peptide synthesis, of self-assembling trans-Azo-YF-NH2 in ambient light; however, irradiation with UV light gives rise to the cis-isomer, which readily hydrolyzes to its amino acid derivatives (cis-Azo-Y + F-NH2) with consequent gel dissolution.