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Zincke Aldehyde
Zincke aldehydes, or 5-aminopenta-2,4-dienals, are the product of the reaction of a pyridinium salt with two equivalents of any secondary amine, followed by basic hydrolysis. Using secondary amines (as opposed to primary amines) the Zincke reaction takes on a different shape forming Zincke aldehydes in which the pyridine ring is ring-opened with the terminal iminium group hydrolyzed to an aldehyde. The use of the dinitrophenyl group for pyridine activation was first reported by Theodor Zincke. The use of cyanogen bromide for pyridine activation was independently reported by W. König: The synthesis and utility of Zincke aldehydes has been reviewed. A variation of the Zincke reaction has been applied in the synthesis of novel indoles: with cyanogen bromide mediated pyridine activation (König method). More recently, an interesting rearrangement of Zincke aldehydes to ''Z''-unsaturated amides was discovered serendipitously while trying to do an Intramolecular Diels-Alder Cycloa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zincke Reaction
The Zincke reaction is an organic reaction, named after Theodor Zincke, in which a pyridine is transformed into a pyridinium salt by reaction with 2,4-dinitro-chlorobenzene and a primary amine. The Zincke reaction should not be confused with the Zincke-Suhl reaction or the Zincke nitration. Furthermore, the Zincke reaction has nothing to do with the chemical element zinc. Reaction mechanism The first reaction is the formation of the ''N''-2,4-dinitrophenyl-pyridinium salt (2). This salt is typically isolated and purified by recrystallization. Upon heating a primary amine with the ''N''-2,4-dinitrophenyl-pyridinium salt (2), the addition of the amine leads to the opening of the pyridinium ring. A second addition of amine leads to the displacement of 2,4-dinitroaniline (5) and formation of the König salt (6a and 6b). The trans-cis-trans isomer of the König salt (6a) can react by either sigmatropic rearrangement or nucleophilic addition of a zwitterionic intermediate to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |