Dearomatization of Furan: Structure of an .eta.2-Furan Complex and a Survey of Its Reactivity

Nitrilium ions – synthesis and applications

“…52 A similar β-addition to nitrilium ions was shown for the analogue η 2 -furan complexes. 53 C-Phenyl nitrilium salts 1-BF 4 reportedly react in high yield with imino-imidazoles 34 to bis-imino-imidazolium salt 35 (Scheme 4e) that are precursors for bis-imino N-heterocyclic carbenes, but the parent imidoyl chloride shows no reactivity. 54 (N-Methyl)(methyl)-1-BF 4 has been shown to react in THF with a lithiated C-methyl imine to generate the BF 2 -adduct of asymmetrically substituted β-diimine 36 in poor yield (Scheme 4f ).…”

The Activation of Aromatic Molecules with Pentaammineosmium(II)

“…Alternatively, Zn°/Hg° amalgam may be used as the reducing agent if the reaction is carried out in methanol. Using this simple procedure, pentaammineosmium(II) complexes have been prepared with a diverse array of η 2 -bound aromatic ligands (Figure ) including benzenes, − anisoles, , anilines, − phenols, ,− naphthalenes, and other polyaromatic hydrocarbons, pyridines, , pyrroles, − furans, ,, and thiophenes, , with yields typically >90%. Where convenient, the ligand is used in approximately a 10-fold excess to minimize the formation of binuclear impurities.…”

“…Given that the rate of 4,5-η 2 to 2,3-η 2 isomerization for the 2,5-dimethylpyrrole complex is similar to that for the benzene complex and that this rate is substantially faster than the corresponding process for the parent pyrrole complex, the 3,4-η 2 isomer is likely only 3−5 kcal/mol higher in energy than its 4,5-η 2 isomer . In contrast to pyrrole, the thiophene and furan complexes of pentaammineosmium(II) appear completely static in 1 H NMR (300 MHz) spectra at 20 °C, which suggests that the 3,4-η 2 isomer is much less accessible for the chalcogen heterocycles. , …”

“…The corresponding intra-ring isomerization rate for naphthalene is also slower than that for benzene, an observation that again reflects the energy difference between inequivalent isomers (i.e., the 3,4-η 2 and 2,3-η 2 isomers for the naphthalene complex). For the heterocycles pyrrole, furan, and thiophene, the pyrrole complex is at least 10 3 times more fluxional at 20 °C than its congeners. ,,

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6 A survey of linkage isomerizations and associated specific rates (20 °C), illustrating the kinetic barrier to metal migration outside aromatic ring.

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Effects of the absorbent types on changes in benzo[a]pyrene and volatile compounds in sesame oil

“…Some furans, such as 5-methylene-2(5H)-furanone, 5-methyl-3(2H)-furanone, 2,5-dimethyl-3-(2H)-furanone, 5-methyl-2-furancarboxaldehyde, and dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone, were significantly reduced after filtration with acid clay combined with PW. This could be due to the relatively polar structure of furan compounds, especially furanones, which have more than one oxygen molecule, and the relatively polar structure of acid clay [11,25].…”