Synthesis and properties of cross-conjugated ω,ω′-bis- dimethylamino ketones and dinitriles with N-acetyl- and N-benzylpiperidine cycles

Article abstract of DOI:10.1007/s11172-011-0306-5

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-tri-methoxypropane 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 Et ₂O · 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-methoxypoly-methine salt. Methylation of 3,5-bis(3- dimethylaminoprop-2-enylidene)-1-benzylpiperidin-4-one with Me ₂SO₄ (1 equiv.) involved cyclic nitrogen atom and resulted in piperidinium salt; heating of the latter with the excess of Me ₂SO₄ afforded doubly charged bis-methoxysulfonate. Starting from 4-methoxytetrahydropyridinium salts, meso- methoxythiapentacarbocyanine dyes were synthesized.