71457-44-8Relevant articles and documents
SELENOPYRYLIUM SALTS IN REACTIONS WITH SODIUM METHOXIDE
Drevko, B. I.,Petrakov, S. N.,Fomenko, L. A.,Zhukov, O. I.,Smushkin, M. I.,et al.
, p. 124 - 126 (2007/10/02)
It was shown by PMR spectroscopy that the reaction of selenopyrylium salts with sodium methoxide gives various reaction products, depending on the number and nature of the substituents at the heteroaromatic cation: 4H-Selenopyrans, a mixture of 4H- and 2H
1H Nuclear Magnetic Resonance Study of Methoxide Addition to Pyrylium and Thiopyrylium Cations; Heteroatom and Substituent Effects
Doddi, Giancarlo,Ercolani, Gianfranco
, p. 271 - 276 (2007/10/02)
Methoxide addition to pyrylium and thiopyrylium salts with various α-substituents (Ph or tBu) and γ-substituents (H, Me, tBu, Et3C, Ph or MeO) in methanol at -40 and 25 deg C has been studied by 1H n.m.r.The composition of the product mixtures, kinetically controlled at -40 deg C and thermodynamically controlled at 25 deg C, gives information on the factors affecting positional selectivity and the relative thermodynamic stability of the addition products (the 2H- and 4H-adduct).The methyl-substituted substrates also undergo deprotonation, to yield the corresponding anhydro-bases.Analysis of heteroatom and substituent effects on the rean course emphasizes the role of polar and steric interactions, and sheds light on the structures of the transition states.
Proton Nuclear Magnetic Resonance Study of the Addition of Methoxide Ion to 2,4,6-Triphenylpyrylium, 2,4,6-Triphenylthiopyrylium, 1,2,4,6-Tetraphenylpyridinium, and 1-(p-Nitrophenyl)-2,4,6-triphenylpyridinium Cations
Aveta, Raffaele,Doddi, Giancarlo,Insam, Normanno,Stegel, Franco
, p. 5160 - 5163 (2007/10/02)
The reactions of 2,4,6-triphenylpyrylium (1a) and 2,4,6-triphenylthiopyrylium (1b) with methoxide ion are shifted toward the formation of adducts, as shown by 1H NMR.The former yields practically only a 2H-pyran adduct in MeCN, Me2SO, or MeOH.In MeOH, 1b yields an adduct with a 2H-thiopyran structure, whereas in MeCN this adduct is obtained together with the isomeric 4H-thiopyran adduct.In Me2SO or MeCN, the 1,2,4,6-tetraphenylpyridinium cation yields a 1,2-dihydropyridine.In contrast, in MeOH this equilibrium is shifted toward the reagents.The lower degree of delocalization of the positive charge in the pyridinium cation seems to be the main cause of its lower tendency to undergo nucleophilic addition.
