- Facile and Stereospecific Synthesis of Various Dienones Using Task-specific Ionic Liquid/Borohydride as Stable and Promoted Hydrogen Release Reagent
-
In this work, for the first time, task-specific ionic liquid, 1-n-butyl-3-methylimidazolium borohydride ([bmim]BH4), was used as the medium as well as reagent for the regiospecific reduction of triarylpyrylium perchlorates to provide aromatic d
- Mouradzadegun, Arash,Ganjali, Mohammad Reza,Sabbagh, Elham,Abadast, Fatemeh
-
p. 3574 - 3577
(2017/11/21)
-
- Substituent effects in reductions of heteroaromatic cations
-
A set of 11 each of 2,4,6-triphenylpyrylium, -thiopyrylium and -N-methylpyridinium tetrafluoroborates carrying a range of substituents in the phenyl rings were prepared. First and second wave reduction potentials were determined. For the thiopyrylium seri
- Heyes, David,Menon, Ramesh S.,Watt,Wiseman, Jake,Kubinski, Przemyslaw
-
p. 689 - 700
(2007/10/03)
-
- Substituent effects in cyanoborohydride reductions of heterocyclic aromatic cations
-
First and second wave E1/2redn potentials have been measured by cyclic voltammetry for a set of fifteen 2,6-diphenyl-4-(X-phenyl)-pyrylium, -thiopyrylium and -N-methylpyridinium tetrafluoroborates, with X = p-CH3, -H, m-Cl, p-CF3 and m,m-(CF3)2.There are linear correlations between Hammett substituent constants and scaled potentials (E/0.05915) giving slopes of ρ = 2.59+/-0.06 (r2 = 0.9984), 2.38+/-0.07 (r2 = 0.9973) and 3.10+/-0.16 (r2 = 0.9918), respectively, for the first wave potentials.Products, rates and kinetic hydrogen isotope effects for reductions of the cations with sodium and tetrabutylammonium cyanoborohydride in acetonitrile solution have been determined.Reaction of the thiopyrylium 2 (X = H) yields kinetically controlled 54:46 mixture of the 4H- and 2H-thiopyrans.With the pyrylium ion 1 (X = H) the 4H- to 2H-ratio is 24:76 with the 2H-pyran suffering electrocyclic ring opening to 1,3,5-triphenylpentadienal.Product ratios are weakly sensitive to substituents on the 4-phenyl, with electron withdrawing groups increasing the amount of 2H-product for both thiopyryliums and pyrylium cations.Reductions are first order in cation and cyanoborohydride.For sodium cyanoborohydride and 2,4,6-triphenylpyrylium, k(25 deg C) = 65.6 dm3 mol-1 s-1 and for 2,4,6-triphenylthiopyrylium. k(25 deg C) = 16.7 dm3 mol-1 s-1, with kinetic isotope effects kBH3CN/kBD3CN) of 1.17 and 1.68, respectively.Logarithms of rate constants correlate with Hammett constants giving ρ = 1.46+/-0.06 (r2 = 0.9951) for the pyrylium series and ρ = 1.12+/-0.08 (r2 = 0.9831) for the thiopyryliums.The N-methylpyridinium ions do not react with cyanoborohydride.The X-ray crystal structure of 2,4,6-triphenyl-N-methylpyridinium tetrafluoroborate has been determined.Dihedral angles about bonds from the pyridinium ring to the 2- and 6-phenyls are larger than corresponding angles in 2,4,6-triphenylpyrylium and 2,4,6-triphenylthiopyryliums and are ascribed to relief of non-bonded interactions between the 2- and 6-phenyls and the N-methyl group.
- Beddoes, Roy,Heyes, David,Menon, Ramesh S.,Watt, C. Ian. F.
-
p. 307 - 320
(2007/10/03)
-
- SYNTHESIS OF 4H-PYRANS BY O-CYCLIZATION OF 1,5-DIKETONES
-
Substituted 4H-pyrans were obtained in high preparative yields by the reaction of 1,5-diketones with acetic anhydride and boron trifluoride etherate in diethyl ether.It is assumed that the heterocyclization of 1,5-diketones includes a step involving the f
- Blinokhvatov, A. F.,Markovtseva, O. V.,Nikolaeva, M. N.
-
p. 266 - 268
(2007/10/02)
-
- Δ3-DIHYDROPYRANS AND TETRAHYDROPYRANS BY REDUCTION OF PYRYLIUM SALTS WITH SODIUM BOROHYDRIDE IN ACETIC ACID
-
The major reduction products with triacetoxyborohydride (NaBH4 in AcOH) of 2,4,6-trisubstituted pyrylium salts bearing alkyl substituents in the 2- and/or 6-position are the Δ3-dihydropyrans with cis 2- and 6-substituents and all-cis-2,4,6-trisubstituted tetrahydropyrans. Δ3-dihydropyrans are shown to be formed via 2H-pyrans by a 1,4 reduction while tetrahydropyrans result from 4H-pyrans by reduction of both enol-ether double bonds.
- Balaban, Teodor-Silviu,Balaban, Alexandru, T.
-
p. 1341 - 1344
(2007/10/02)
-