77213-08-2Relevant academic research and scientific papers
Pentadienyl type lithium and potassium species: The regioselectivity of their reactions with electrophiles
Schlosser,Zellner,Leroux
, p. 1830 - 1836 (2007/10/03)
Seven structurally distinct pentadienyl type lithium and potassium compounds were screened against a variety of electrophiles in order to assess the regioselectivity of the trapping reactions. Organoborates and analogs thereof (fluorodimethoxyborane) proved to be perfectly regioreliable attacking only unsubstituted terminal positions and thus providing, after oxidation, exclusively primary allylic alcohols. 2,4-Pentadienyllithiums or -potassiums, that carry a methyl group at the 1- or 3-position, exhibit the same extreme regioselectivity towards halotrialkylsilanes or carbon dioxide. Although the unsubstituted parent compounds combine with such electrophiles still preferentially at the terminal position, considerable proportions of branched products are concomitantly formed as well (1/3-attack ratios ranging from 2:1 to >20:1). Hydroxyalkylating and alkylating reagents such as formaldehyde, oxirane or butyl iodide invariably afford regioisomeric mixtures generally varying in composition between 3:1 and 1:3. The condensation reaction with halotrialkylsilanes appears to follow a concerted (SN2-like) rather than an addition/elimination (ate complex-mediated) mechanism.
Chemistry of Dienyl Anions. IV. Geometry of Pentadienyl Anions in Solution and in the Solid State Determined by Regioselective Trimethylsilylation and NMR
Yasuda, Hajime,Yamauchi, Michihide,Ohnuma, Yasuo,Nakamura, Akira
, p. 1481 - 1491 (2007/10/02)
The configurational analysis of a series of alkyl substituted pentadienyl anions in THF was examined by trimethylsilylation and from the variable temperature 1H- and 13C-NMR spectra.Potassium pentadienide, -2-methylpentadienide or -2,4-dimethylpentadienide produced preferentially (Z)-2,4-pentadienyltrimethylsilane or its methyl substituted analogues to indicate that these compounds have the "U"-shaped structure in solution.By contrast, trimethylsilylation of potassium pentadienide and -2-methylpentadienide in the crystalline state produced the (E)- and the (E),(Z)-isomers, respectively, suggesting that the geometry is drastically changed to the "W"- or "S"-shaped by the medium effect.The W-shaped structure of potassium 3-methylpentadienide in THF and in the solid state is exceptional.Geometry of trapped products of potassium cycloheptadienide and -cyclooctadienide is also (Z) but the silylation occurred on the central carbon in contrast to the terminal silylation seen for the open-chain pentadienides.Geometry of these dienyl anions determined by NMR below -30 deg C was consistent with the result obtained from trimethylsilylation.Superficial conflict between MINDO/3 prediction and the experimental evidence was reasonably reconciled by considering contact ion pair for potassium pentadienide in THF and more strongly-solvated ion pair for the lithium analogues.
