Zh. A. Krasnaya, E. O. Tret’yakova, V. Kachala
Oct 1, 2011
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Journal
Russian Chemical Bulletin
Abstract
Reactions of N-acetyl- and N-benzyl-4-piperidones with aminal of β-dimethylaminoac-rolein yielded ketocyanines bearing piperidine cycle. Reaction of 3-dimethylamino-1,1,3-trimethoxypropane with 1-acetylpiperidin-4-ylidenemalononitrile in the presence of ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4), resulted in cross-conjugated ω,ω’-dimethylamino dinitrile. Protonation of ketocyanines bearing N-acetyl- and N-benzyl-piperidine cycles with Et2O·HBF4 (1 equiv.) furnished piperidinium salts, while protonation of the latter with Et2O·HBF4 (2 equiv.) afforded doubly charged 4-hydroxypolymethine salts. Unlike protonation, reaction of 3,5-bis(3-dimethylaminoprop-2-enylidene)-1-acetylpiperidin-4-one with Me2SO4 involved only the oxygen atom and led to a singly charged 4-methoxypolymethine salt. Methylation of 3,5-bis(3-dimethylaminoprop-2-enylidene)-1-benzylpiperidin-4-one with Me2SO4 (1 equiv.) involved cyclic nitrogen atom and resulted in piperidinium salt; heating of the latter with the excess of Me2SO4 afforded doubly charged bis-methoxysulfonate. Starting from 4-methoxytetrahydropyridinium salts, meso-methoxythiapentacarbocyanine dyes were synthesized.