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Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoquinoline is used to make reference to isoquinoline derivatives. 1-Benzylisoquinoline is the structural backbone in many naturally occurring alkaloids such as papaverine.
The reaction below shows the acid-promoted synthesis of isoquinoline from benzaldehyde and a 2,2-dialkoxyethylamine. [5]Pomeranz-Fritsch-Reaktion-Übersichtsreaktion. Various alkyl groups, e.g. methyl and ethyl groups, can be used as substituent R.
Replacing an indole with a 3,4-dimethoxyphenyl group give the reaction named the Pictet–Spengler tetrahydroisoquinoline synthesis. Reaction conditions are generally harsher than the indole variant, and require refluxing conditions with strong acids like hydrochloric acid, trifluoroacetic acid or superacids.
It involves an additional dehydration under the same conditions as the cyclization, giving an isoquinoline. [1] [2] As with the Bischler–Napieralski reaction, the Pictet–Gams reaction requires a strongly dehydrating Lewis acid, such as phosphoryl chloride or phosphorus pentoxide.
Therefore, studies in which either the product or an intermediate is an isoquinoline, the Gabriel–Colman rearrangement can be utilized. This reaction has been utilized in the production of intermediates for the synthesis of potential anti-inflammatory agents. [ 7 ]
Skraup synthesis using ferrous sulfate, glycerol, aniline, nitrobenzene, and sulfuric acid. A number of other processes exist, which require specifically substituted anilines or related compounds: Camps quinoline synthesis using an o-acylaminoacetophenone and hydroxide; Friedländer synthesis using 2-aminobenzaldehyde and acetaldehyde
The reaction allows the synthesis of 1-, 4-, and N-substituted 1,2,3,4-tetrahydroisoquinolines and also 1-, and 4-substituted isoquinolines. General Reaction Scheme
The mechanism of the Pfitzinger reaction. The reaction of isatin with a base such as potassium hydroxide hydrolyses the amide bond to give the keto-acid 2.This intermediate can be isolated, but is typically not.