In decarboxylation

The Gabriel-Colman reaction has been used to prepare 3-alkyl isoquinoline 1,4-diols. Phthalimides 8 and 9 rearrange as expected when treated with alkoxides. Further treatment with sodium ethoxide results in decarboxylation and the expected isoquinolinone 1,4-diols 12 and 13. 

Electrolysis of carboxylate ions, which results in decarboxylation and combination of the resulting radicals, is called the Kolbe reaction or the Kolbe electrosynthesis. 

NAD and NADP and FMN and FAD, respectively. Pantothenic acid is a component of the acyl group carrier coenzyme A. As its pyrophosphate, thiamin participates in decarboxylation of a-keto acids and folic acid and cobamide coenzymes function in one-carbon metabolism. 

Attempts to isolate pure C-AIR (107) were unsuccessful due to its instability in acid solution and toward heat resulting in decarboxylation giving AIR (106) (57JA1511). Using UV spectrometry, transformation of C-AIR... 

Dauben, W. G., and P. Coad Oxydation in Decarboxylation of Acids with... 

These enzymes invariably involve a cofactor, pyridoxal phosphate (vitamin B6). In addition, pyridoxal phosphate is also required for most decarboxylations, racemizations, or elimination reactions in which an amino acid is a substrate. Pyridoxal phosphate is not involved in decarboxylations in which the substrate is not an amino acid. So if a question... 

The fact that 27 is produced by dehydration both of uronic acids and of pentoses has led to the suggestion112 that pentoses may be intermediates in decarboxylation reactions of uronic acids, and that treatment of such glycuronans as pectin with strong acids results in the production of pentosans.113 Little evidence supports this theory, be-... 

Thiamine pyrophosphate is a coenzyme and the active form of vitamin B. It functions as coenzyme in decarboxylation of a-keto acid and in hexose monophosphate shunt. 

Reaction with cold nitric acid results primarily in the formation of 5-nitrosalicylic acid [96-97-9]. However, reaction with fuming nitric acid results in decarboxylation as well as the formation of 2,4,6-trinitrophenol [88-89-1] (picric acid). Sulfonation with chlorosulfonic acid at 160°C yields 5-sulfosalicylic acid [56507-30-3]. At higher temperatures (180°C) and with an excess of chlorosulfonic acid, 3,5-disulfosalicylic acid forms. Sulfonation with liquid sulfur trioxide in tetrachloroethylene leads to a nearly quantitative yield of 5-sulfosalicylc acid (1). 

A clever application of this reaction has recently been carried out to achieve a high yield synthesis of arene oxides and other dihydroaromatic, as well as aromatic, compounds. Fused-ring /3-lactones, such as 1-substituted 5-bromo-7-oxabicyclo[4.2.0]oct-2-en-8-ones (32) can be readily prepared by bromolactonization of 1,4-dihydrobenzoic acids (obtainable by Birch reduction of benzoic acids) (75JOC2843). After suitable transformation of substituents, mild heating of the lactone results in decarboxylation and formation of aromatic derivatives which would often be difficult to make otherwise. An example is the synthesis of the arene oxide (33) shown (78JA352, 78JA353). 

Nevertheless, the full-blown mechanism that showed the role of the coenzyme was only written out in detail by Braunstein and M. M. Shemyakin in 1953 (Braunstein and Shemyakin, 1952, 1953). Their formulae (2), complete with the curved arrow notation of physical organic chemistry, clearly pointed out the role of the coenzyme as an electron sink in a ketimine mechanism. They showed how the coenzyme can function in transamination, racemization and, with some help from Hanke and his collaborators (Mandeles et al 1954), in decarboxylation. The mechanisms they advanced were exactly what we would postulate today, and constituted an early and successful application of theory to mechanistic enzymology. But it must be admitted that the theory appealed because it was reasonable the authors had little or no evidence, in terms of physical organic chemistry, to support their formulation, which is shown in part below. 

Decarboxylation temperatures much lower than those used above have been reported. For example, treatment of diisopropyl 3,3-dimethoxycyclobutane-l, 1-dicarboxylate with 20% hydrochloric acid resulted in decarboxylation of the in situ formed diacid 2 at 100°C (reflux) to give 3-oxocyclobutanecarboxylic acid (3) in 97% yield.2... 

Heating dimethyl l-cyanocyclobutane-l,2-dicarboxylate to 150°C in an aqueous environment resulted in decarboxylation to give a mixture of methyl cis- and fra s-2-cyanocyclobutanecar-boxylate (4).6,7... 

The preferred reagent for Hunsdiecker-type reactions is lead(IV) acetate in the presence of an inorganic halide.18,19 The yields are usually good to excellent. Reaction of cyclobutanecar-boxylic acid with lead(IV) acetate in the presence of lithium chloride gave chlorocyclobutane (1) in good yield.18 Other carboxylic acids reacted under similar conditions.18 However, care should always be taken when lead(IV) acetate is used, as the use of this reagent in the absence of the halide results in decarboxylative elimination to give an alkene, which is found as a byproduct.19... 

Electrolysis of carboxylate ions, which results in decarboxylation and combination of the resulting radicals, is called the Kolbe reaction. 30 It is used to prepare symmetrical RR, where R is straight- or branched-chained, except that little or no yield is obtained when there is a branching. The reaction is not successful for R = aryl. Many functional groups... 

Many addition and elimination reactions, e.g., the hydration of aldehydes and ketones, and reactions catalyzed by lyases such as fumarate hydratase are strictly reversible. However, biosynthetic sequences are often nearly irreversible because of the elimination of inorganic phosphate or pyrophosphate ions. Both of these ions occur in low concentrations within cells so that the reverse reaction does not tend to take place. In decarboxylative eliminations, carbon dioxide is produced and reversal becomes unlikely because of the high stability of C02. Further irreversibility is introduced when the major product is an aromatic ring, as in the formation of phenylpyruvate. 

Below the structures of the adducts in Eq. 14-20 are those of a 2-oxo acid and a (3-ketol with arrows indicating the electron flow in decarboxylation and in the aldol cleavage. The similarities to the thiamin-dependent cleavage reaction are especially striking if one remembers that in some aldolases and decarboxylases the substrate carbonyl group is first converted to an N-proto-nated Schiff base before the bond cleavage. 

Special azapeptides are those with C-terminal azaamino acid residues that can only be obtained as esters or amides the corresponding free acids are not available because of their lability that results in decarboxylation to hydrazides. 

Further irradiation results in decarboxylation and the formation of cyclobutadiene... 

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