The relative electron donating ability of substituents, determined in 2,6-disubstituted pyrylium cations
摘要:
The carbon-13 NMR spectra of a series of 2,6-disubstituted pyrylium compounds have been investigated. The chemical shift of C(4) is a measure of the charge density in that position of the ring. The variation of the chemical shift with the change of substituent is determined by the ability of substituents to delocalize the positive charge from C(4), an effect which for substituents at C(2) and C(6) is free from any other shielding or deshielding effects. The electron-donating ability of substituents vary in the order: H < i-Pr < Me < p-ClC6H4 < p-FC6H4 less-than-or-equal-to Ph << 2-thienyl less-than-or-equal-to c-Pr less-than-or-equal-to p-MeOC6H4. The ordering of alkyl groups indicates that C-H hyperconjugation is stronger than C-C hyperconjugation. For the aryl substituents the chemical shifts are correlated linearly with the partial rate factor (log (P(f)) for the protiodesilylation of the parent arenes. The ability of cyclopropyl to delocalize the positive charge is similar to that of 2-thienyl and p-anisyl.
Pharmacological properties of pyridinium salts, pyrazolines, and pyrazoles
作者:É. A. Zvezdina、M. P. Zhdanova、I. I. Nechayuk、I. A. Barchan、Yu. N. Simkina、T. A. Buchnaya
DOI:10.1007/bf00763700
日期:1986.11
6]; drugs have also been found among pyrazoline and pyrazolederivatives [8]. This work presents information on the investigation of the antimicrobial, neurotropic, and fungicidal action of pyridinium salts (III), bis-pyridinium salts (IV), pyrazolines (V), and pyrazolo[l,5-c]pyrimidine (VI), produced in the recyclization of 2,6-diarylpyrilium perchlorates (I) under the action of amines, semi-, and
One-Pot Synthesis of 2,6-Di-<i>t</i>-butyl- and 2,6-Diarylthiopyrylium Perchlorates
作者:Giancarlo Doddi、Gianfranco Ercolani
DOI:10.1055/s-1985-31351
日期:——
The title compounds were prepared by reaction of the corresponding methyl ketone with an excess of triethyl orthoformate in an acidic medium (acetic anhydride/perchloric acid) under a hydrogen sulfide stream.