1,1-Dicarboxylic acids, decarboxylation esterification

Synthetic and degradative use has been made in several instances of the easy decarboxylation of phenanthridine-6-carboxylio acids.30, 80, 324 The corresponding iV-oxide is decarboxylated by heating in aqueous sulfuric acid.77 Phenanthridine-3,8-dicarboxylic acids are more resistant to decarboxylation, which can be achieved (in poor yield) by heating with copper powder in quinoline.194 The usual carboxyl derivative inter con versions (esterification, amide formation, ester and amide hydrolyses, etc.) proceed normally with both phenanthridine-6-carboxylic acid and its A-oxide,77, 232, 352 although an unsuccessful attempt to prepare 6-acetylphenanthridine from the acid with methyllithium has been reported.232... 

The total synthesis of (+ )-dehydroheliotridine (4), a toxic metabolite of the pyrrolizidine alkaloids (e.g. lasiocarpine and heliotrine), has also been described.2 The pyrrole ring was obtained by reaction of l,6-dihydroxy-2,5-dicyanohexa-l,3,5-triene-l,6-dicarboxylic ester (5) with j3-alanine, which afforded the N-substituted pyrrole ester (6), together with the appropriate amide of oxalic acid. Careful hydrolysis of (6) with dilute alkali afforded the related tricarboxylic acid, which was converted, by Dieckmann cyclization, hydrolysis and decarboxylation, into the keto-acid (7). Esterification of (7) with diazomethane, followed by reduction with lithium aluminium hydride, finally afforded ( )-dehydroheliotridine (4), identical, except in optical rotation, with dehydroheliotridine obtained earlier by Culvenor et al.3... 

Pyridazine-3,6-dicarboxylic acid undergoes facile decarboxylation in acid but esterification is successfully accomplished by adding thionyl chloride to alcoholic solutions of the diacid at — 30°C... 

Pyrrole-2-carboxylic acid esters have been prepared from ethyl chloroformate and pyrrolylmagnesium bromide1 2 or pyrrolyllithium,3 by hydrolysis and decarboxylation of dimethyl pyrrole-1,2-dicarboxylate followed by re-esterification of the 2-acid4 and by oxidation of pyrrole-2-carboxaldehyde followed by esterification with diazomethane.4... 

A mixture of lupinine and epilupinine is obtainable by the following series of reactions. The betaine XXVI on cyclic hydrogenation and subsequent decarboxylation with 20 % hydrochloric acid gives a mixture of epimeric lupininic acids (XXIX). The dicarboxylic ester XXVIII is also obtained by the mercuric acetate dehydrogenation of the piperidine derivative XXX and by the alkylation of monomeric piperideine with a y-bromopropylmalonic ester. The last route is presumably a first Mannich condensation followed by an alkylation. Hydrolysis of the malonic esters, decarboxylation (XXIV), esterification, and reduction with lithium aluminum hydride complete the synthesis of a mixture which consists of 80% dZ-epilupinine and 20% dMupinine. Thermal... 

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