The Gould–Jacobs reaction is an organic synthesis for the preparation of quinolines and 4‐hydroxyquinoline derivatives. The Gould-Jacobs reaction is a series of reactions. The series of reactions begins with the condensation/substitution of an aniline with alkoxy methylenemalonic ester or acyl malonic ester, producing anilidomethylenemalonic ester. Then through a 6 electron cyclization process, 4-hydroxy-3-carboalkoxyquinoline is formed, which exist mostly in the 4-oxo form. Saponification results in the formation of an acid. This step is followed by decarboxylation to give 4-hydroxyquinoline. The Gould-Jacobs reaction is effective for anilines with electron‐donating groups at the meta‐position. Specifically, 4-quinolinol can be synthesized. In this reaction aniline or an aniline derivative first reacts with malonic acid derivative ethyl ethoxymethylenemalonate with substitution of the ethoxy group by nitrogen. A benzannulation takes place by application of heat to a quinoline. The ester group is hydrolysed by sodium hydroxide to the carboxylic acid and decarboxylation again by application of heat to 4-hydroxyquinoline. Extension of the Gould-Jacobs approach can prepare unsubstituted parent heterocycles with fused pyridine ring of Skraup type. Further reading:
Mechanism
The mechanism for the Gould–Jacobs reaction begins with a nucleophilic attack from the amine nitrogen follows by the loss of ethanol to form the condensation product. A 6 electron cyclization reaction with the loss of another ethanol molecule forms a quinoline. The enol form can be represented from the keto form through keto-enol tautomerism. Protonation of the nitrogen forms ethyl 4-oxo-1,4-dihydroquinoline-3-carboxylate.
Examples and applications
An example is the synthesis of 4,7-dichloroquinoline.
Floctafenine and glafenine are a pair of fenamate NSAIDs whose syntheses rely on the Gould–Jacobs reaction.
Another example is in the synthesis of antimalarials as aminoalkylamino derivatives of 2,3-dihydrofuroquinolines The Gould reaction is also used to convert 5-aminoindole to quinolines for the purpose of synthesizing pyrazolopyrroloquinolin-3-one derivatives as modified pyrazoloquinolinone analogs. These compounds have the potential to act as antagonists at central benzodiazepine receptors in Xenopuslaevis oocytes. File:Gould-Jacobs_reaction_on_5-aminoindole.png|center|500px|Conversion of 5-aminoindole to quinolines by the Gould-Jacobs reaction for the purpose of synthesizing pyrazolopyrroloquinolin-3-one derivatives The Gould‐Jacobs reaction has also been used both conventionally with condensation steps and acyclic intermediated and with single step microwave irradiation to synthesize ethyl 4‐oxo‐8,10‐substituted‐4,8‐dihydropyrimidopyrrolopyrimidine‐3‐carboxylates. File:Synthesis_of_ethyl_4‐oxo‐8,10‐substituted‐4,8‐dihydropyrimidopyrrolopyrimidine‐3‐carboxylates_by_the_Gould-Jacobs_reaction.png|center|500px|Conventional and microwave radiation approach to synthesize ethyl 4‐oxo‐8,10‐substituted‐4,8‐dihydropyrimidopyrrolopyrimidine‐3‐carboxylates by the Gould-Jacobs reaction
