19980-46-2Relevant academic research and scientific papers
Thermal and photochemical solvolysis of (E)- and (Z)-2-phenyl-1-propenyl(phenyl)iodonium tetrafluoroborate: Benzenium and primary vinylic cation intermediates
Gronheid,Lodder,Ochiai,Sueda,Okuyama
, p. 8760 - 8765 (2007/10/03)
The thermal and photochemical solvolysis of the two stereoisomeric 2-phenyl-1-propenyl(phenyl)-iodonium tetrafluoroborates has been investigated in alcoholic solvents of varying nucleophilicity. The product profiles and rates of product formation in the thermal reaction are all compatible with a mechanism involving cleavage of the vinylic C - I bond assisted by the group in the trans position (methyl or phenyl), always leading to rearranged products. Depending on the nucleophilicity of the solvent, the primarily formed cations may or may not further rearrange to more stable isomers. The less reactive Z compound also yields some unrearranged vinyl ether product in the more nucleophilic solvents via an in-plane SN2 mechanism. The mechanism of the photolysis involves direct, unassisted cleavage of the vinylic, and aromatic, C - I bond in an SN1 mechanism. This produces a primary vinyl cation, which is partially trapped prior to rearrangement in methanol. The unrearranged vinyl ethers are mainly formed with retention of configuration via a λ3-iodonium/solvent complex in an SNi mechanism. Thermal and photochemical solvolyses of iodonium salts are complementary techniques for the generation of different cation intermediates from the same substrate.
Tris(dialkylamino)sulfonium Enolates. Synthesis, Structure, and Reactions
Noyori, R.,Nishida, I.,Sakata, J.
, p. 1598 - 1608 (2007/10/02)
A mixture of an enol trimethylsilyl ether and a fluoride salt exists in a dynamic equilibrium with an enolate species and fluorotrimethylsilane.Evacuation of an equimolar mixture of an enol trimethylsilyl ether of benzyl methyl ketone and tris(diethylamino)sulfonium (TAS) difluorotrimethylsiliconate produces fluorotrimethylsilane as the volatile fraction and the corresponding TAS enolate as air-sensitive crystals.The conductivity measurement and the 1H and 13C NMR analysis have substantiated the ionic nature of the TAS enolate in THF.The NMR chemical shifts are interpreted in terms of the electron distribution.The isolated TAS enolate undergoes O-acetylation with acetic anhydride and C-alkylation with methyl iodide exclusively.TAS enolate intermediates generated in situ from a series of enol silyl ethers and TAS difluorotrimethylsiliconate react with various active organic halides under mild conditions to give the regiospecific C-alkylation products.The in situ formed enolates react with aldehyde substrates to afford the β-trimethylsiloxy ketone adducts.In most cases, the reaction is kinetically controlled and the major products have erythro stereochemistry regardless of enolate configuration.This aldol reaction is postulated to proceed via an acyclic, extended transition state, in contrast to ordinary aldol reactions of Lewis acid coordinated enolates, which take place by way of six-membered chelate transition states.
Regio- and Stereo-selectivity of Acetoxymercuration of Acetylenes
Uemura, Sakae,Miyoshi, Haruo,Okano, Masaya
, p. 1098 - 1103 (2007/10/02)
Acetoxymercuration of alkylphenylacetylenes (PhCCR; R = Me, Et, Prn, or Bun) (1) in acetic acid at 20 - 60 deg C proceeds completely in a trans-fashion to afford a regioisomeric mixture of two vinylmercury(II) compounds, Ph(OAc)C=C(HgCl)R (2) and Ph(HgCl)C=C(OAc)R (3), the extent of attack of Hg at the carbon α to alkyl group to form (2) being increased upon increasing the carbonyl chain length of the alkyl group .A bridged mercurinium ion intermediate in which phenyl and alkyl groups are bent toward the attacking side of acetate anion is proposed for explaining a marked dependence of the isomer ratio (2):(3) on the kind of alkyl groups.Similar treatment of diphenylacetylene at 20 - 95 deg C gives only the cis-adduct as reported previously, while that of diethyl-acetylene affords the trans-adduct and a mixture of trans- and cis-adduct at 20 deg C and at 65 deg C, respectively.The NaBH4 reduction of (2, R = Me) in neutral condition produces a mixture of (Z)- and (E)-1-acetoxy-1-phenylpropene (ca. 3-5:1) in contrast to the reduction of thallium analogue of (2) which gives only the Z-isomer.
