Carboxylic acids decarboxylative

Practically all pyridazine-carboxylic and -polycarboxylic acids undergo decarboxylation when heated above 200 °C. As the corresponding products are usually isolated in high yields, decarboxylation is frequently used as the best synthetic route for many pyridazine and pyridazinone derivatives. For example, pyridazine-3-carboxylic acid eliminates carbon dioxide when heated at reduced pressure to give pyridazine in almost quantitative yield, but pyridazine is obtained in poor yield from pyridazine-4-carboxylic acid. Decarboxylation is usually carried out in acid solution, or by heating dry silver salts, while organic bases such as aniline, dimethylaniline and quinoline are used as catalysts for monodecarboxylation of pyridazine-4,5-dicarboxylic acids. 

Benzimidazole-2-carboxylic acid decarboxylation, 5, 435 Benzimidazole-3-carboxylic acid, 1-hydroxy-ethyl ester synthesis, 6, 407 Benzimidazoles acidity, 5, 50, 385, 386 acylation, 5, 71, 391, 402, 417 2V-alkyl-... 

Benzisoxazole-3-carboxylic acid decarboxylated ring opening, 6, 31 reactions, 6, 52... 

Claisen condensation, 6, 156 reactions, S, 92 IsothiazoIe-3-carboxyIic acids decarboxylation, 6, 156 Isothiazole-4-carboxylic acids decarboxylation, 6, 156 Isothiazole-5-carboxylic acids decarboxylation, S, 92 6, 156 IR spectroscopy, 6, 142 Isothiazole-3-diazonium borofluoride decomposition, 6, 158 IsothiazoIe-4-diazonium chloride, 3-methyl-reactions with thiourea, 6, 158 Isothiazole-5-diazonium chloride, 4-bromo-3-methyl-halogen exchange, 6, 163 Isothiazole-5-diazonium chloride, 3-methyl-reactions... 

Naphthothiazole-2-carboxylic acid decarboxylation, 6, 279 Naphthothiene nomenclature, 1, 21 Naphthothiete, S-methyl-reactions... 

Claisen ester condensation, 6, 279 Thiazolecarboxylic acid chlorides reactions, 6, 279-280 Thiazolecarboxylic acid hydrazides synthesis, 6, 280 Thiazolecarboxylic acids acidity, 6, 279 decarboxylation, 6, 279 reactions, S, 92 6, 274 Thiazole-2-carboxylic acids decarboxylation, S, 92 Thiazole-4-carboxylic acids stability, S, 92 Thiazole-5-carboxylic acids decarboxylation, S, 92 Thiazole-4,5-dicarboxylic acid, 2-amino-diethyl ester reduction, 6, 279 Thiazole-4,5-dicarboxylic acids diethyl ester saponification, 6, 279 Thiazolediones diazo coupling, 5, 59 Thiazoles, 6, 235-331 ab initio calculations, 6, 236 acidity, S, 49 acylation, 6, 256 alkylation, S, 58, 73 6, 253, 256 analytical uses, 6, 328 antifogging agents... 

As expected for A-heterocyclic a-carboxylic acids, j8-carboline-l-carboxylic acids decarboxylate readily on heating and... 

In the electrolysis of quinuchdine-2-carboxylic acid decarboxylation occurs without rearrangement (Table 12, No. 5). Stereospecifically substituted cyclopentanes, that... 

A. Joll, T. Huynh and A. Heitz, Off line tetramethylammonium hydroxide thermochemolysis of model compound aliphatic and aromatic carboxylic acids decarboxylation of some ortho and/ or para substituted aromatic carboxylic acids, J. Anal. Appl. Pyrol., 70, 151 167 (2003). 

Similarly, acetylation of thieno[3,2-6]thiophene (2) afforded 2-acetyl-thieno[3,2-6]thiophene, which was converted into methyl n-hexyl ketone by desulfurization with Raney nickel. Oxidation of 2-acetylthieno-[3,2-i]thiophene followed by nitration gave 5-nitrothieno[3,2-6]-thiophene-2-carboxylic acid. Decarboxylation of the latter furnished 2-nitrothieno[3,2-ft]thiophene identical with the compound obtained by direct nitration of thienothiophene 2 [Eq. (60)]. 

It has been shown that thiophene-2,3-dicarboxyIic acid is preferentially esterified in the 2-position also, selective hydrolysis of the 2,3-diester results in the formation of the 2-carboxylic acid. Decarboxylation during electrophilic substitution is a well-recognized... 

Aminobenzo[6]thiophene-2-carhoxylic acids are conveniently obtained by reduction of the corresponding nitro compound.152,185,333, 334,33c, 338,497 Djazotization of these, followed by the usual replacement reactions of the diazonium group, provides many substituted benzo[6]thiophene-2-carboxylic acids, decarboxylation of which leads to some otherwise rather inaccessible benzo[6]thiophenes. 5-Hydroxy-benzo[6]thiophene-2-carboxylic acid is most conveniently prepared from the corresponding amino compound by means of the Bucherer reaction,338,497 in which the dicarboxylic acid (303) is formed as a by-product.152... 

H- Benzimidazole, 2,2-pentamethylene-reduction, 5, 423 Benzimidazole-2-carbaldehyde oximes, 5, 436 Benzimidazolecarbaldehydes oxidation, 5, 437 Benzimidazole-2-carbamates 5-substituted as anthelmintics, I, 202 Benzimidazole-l-carboxylic acid, 2-amino-methyl ester reactions, 5, 453 Benzimidazole-2-carboxylic acid decarboxylation, 5, 435 Benzimidazole-3-carboxylic acid, 1-hydroxy-ethyl ester synthesis, 6, 407 Benzimidazoles acidity, 5, 50, 385, 386 acylation, 5, 71, 391, 402, 417 N-alkyl-... 

We have presented evidence that pyrrole-2-carboxylic acid decarboxylates in acid via the addition of water to the carboxyl group, rather than by direct formation of C02.73 This leads to the formation of the conjugate acid of carbonic acid, C(OH)3+, which rapidly dissociates into protonated water and carbon dioxide (Scheme 9). The pKA for protonation of the a-carbon acid of pyrrole is —3.8.74 Although this mechanism of decarboxylation is more complex than the typical dissociative mechanism generating carbon dioxide, the weak carbanion formed will be a poor nucleophile and will not be subject to internal return. However, this leads to a point of interest, in that an enzyme catalyzes the decarboxylation and carboxylation of pyrrole-2-carboxylic acid and pyrrole respectively.75 In the decarboxylation reaction, unlike the case of 2-ketoacids, the enzyme cannot access the potential catalysis available from preventing the internal return from a highly basic carbanion, which could be the reason that the rates of decarboxylation are more comparable to those in solution. Therefore, the enzyme cannot achieve further acceleration of decarboxylation. In the carboxylation of pyrrole, the absence of a reactive carbanion will also make the reaction more difficult however, in this case it occurs more readily than with other aromatic acid decarboxylases. 

In ergosterol biosynthesis, side chain alkylation of lanosterol normally takes place to build 24-methylenedihydrolanosterol, which itself is then the substrate for demethylation reactions at and C. The C -demethylation has been studied in detail. It is an oxidative demethylation catalyzed by a cytochrome P -system. The first step involved in this reaction is the hydroxylation of the Cj -methy1-group to form the C -hydroxymethyl derivative. A second hydroxylation and loss of water lead to the C -formyl intermediate, which is hydroxylized a third time to form the corresponding carboxylic acid. Decarboxylation does not directly take place, but proceeds instead by abstraction of a proton from C, followed by elimination and formation of a A 4-double bond. The NADPH-dependent reduction of the A14 -double bond finishes the demethylation reaction. Subsequently, demethylation at has to take place twice, followed by a dehydrogenation reaction in A" -position and isomerization from A8 to A7 and A24(28) to A22. respectively. 

Except for some activated acids, for example aryl carboxylic acids, decarboxylation of free carboxylic acids is often difficult [17]. Under the reaction conditions used for of the deuteration in Scheme 6 (i.e. Pd/C catalyst, in deuterium oxide at 250 C/4-5 MPa), decarboxylation was observed - a carboxyl group is exchanged with a D atom, accompanied by H-D exchange reaction on all carbons [18]. 

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