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The Kröhnke method in this synthesis was crucial due to the failure of other cyclization techniques such as the Glaser coupling or Ullmann coupling. Figure 13. Another use of the Kröhnke pyridine synthesis was the generation of a number of 2,4,6-trisubstituted pyridines that were investigated as potential topoisomerase 1 inhibitors.
Methylpyridinium is prepared by treating pyridine with dimethylsulfate: [2]. C 5 H 5 N + (CH 3 O) 2 SO 2 → [C 5 H 5 NCH 3] + CH 3 OSO − 3. It is found in some coffee products. [3] It is not present in unroasted coffee beans, but is formed during roasting from its precursor chemical, trigonelline. [3]
Preparation [ edit ] 3-Aminopyridine is prepared by heating nicotinamide with sodium hypobromite ( Hofmann rearrangement ), which is in turn prepared in situ by the reaction of sodium hydroxide and bromine at 70 °C.
The Chichibabin pyridine synthesis (/ ˈ tʃ iː tʃ iː ˌ b eɪ b iː n /) is a method for synthesizing pyridine rings. The reaction involves the condensation reaction of aldehydes, ketones, α,β-Unsaturated carbonyl compounds, or any combination of the above, with ammonia. [1] It was reported by Aleksei Chichibabin in 1924.
The Kröhnke pyridine synthesis provides a fairly general method for generating substituted pyridines using pyridine itself as a reagent which does not become incorporated into the final product. The reaction of pyridine with bromomethyl ketones gives the related pyridinium salt, wherein the methylene group is highly acidic.
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.
In organic synthesis, PPTS is used as a weakly acidic catalyst, providing an organic soluble source of pyridinium (C 5 H 5 NH +) ions.For example, PPTS is used to deprotect silyl ethers or tetrahydropyranyl ethers when a substrate is unstable to stronger acid catalysts.
Upon metabolism, 1,4-DHP based antihypertensive drugs undergo oxidation by way of cytochrome P-450 in the liver and are thus converted to their pyridine derivatives. [11] As a result, particular attention has been paid to the aromatization of 1,4-DHPs as a means to understand biological systems and so as to develop new methods of accessing ...