Decarboxylation methylenemalonic ester

The Gould-Jacobs reaction is a sequence of the following reactions (1) condensation of an arylamine 1 with either alkoxy methylenemalonic ester or acyl malonic ester 2 providing the anilidomethylenemalonic ester 3 (2) cyclization of 3 to the 4-hydroxy-3-carboalkoxyquinoline 4 (3) saponification to form acid 5, and (4) decarboxylation to give the 4-hydroxyquinoline 6. All steps of this process will be described herein with emphasis on the formation of intermediates like 3 and 4. 

The tert-butyl esters of 2-pyrrolylaminomethylenemalonates (1438, R2 = COO/Bu) were selectively hydrolyzed with methanesulfonic acid or concentrated sulfuric acid at 0°C or at ambient temperature to afford the corresponding carboxylic acids (1438, R2 = COOH) in 26-98% yields. The carboxylic acid (1438, R = Me, R1 = H, R2 = COOH) underwent facile decarboxylation upon heating at 190-200°C to give 2-pyrrolylamino-methylenemalonate (1438, R = Me, R1 = R2 = H) in 73% yield (85JHC1429). 

Olefinic esters may be obtained directly by the Knoevenagel reaction. Alkyl hydrogen malonates are used in place of malonic acid. Decarboxylation then gives the ester directly as in the preparation of ethyl 2-heptenoate (78%) and methyl m-nitrocinnamate (87%). Alkyl hydrogen malonates are readily available by partial hydrolysis of dialkyl malonates. The use of malonic ester in the condensation leads to olefinic diesters, namely, alkylidenemalonates such as ethyl heptylidenemalonate (68%). A small amount of organic acid is added to the amine catalyst since the salts rather than the free amines have been shown to be the catalysts in condensations of this type. Various catalysts have been studied in the preparation of diethyl methylenemalonate. Increased yields are obtained in the presence of copper salts. Trimethylacetalde-hyde and malonic ester are condensed by acetic anhydride and zinc chloride. Acetic anhydride is also used for the condensation of furfural and malonic ester to furfurylidenemalonic ester (82%). ... 

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