Persulfate decarboxylation

Silver-catalyzed persulfate decarboxylation of carboxylic acids in chloroform provides the noralkane in modest to good yields. Only a limited number of examples with simple aliphatic carboxylic acids are known. 

The decarboxylation reactions of fluonnated carboxylic acids are similar to those of their nonfluonnated counterparts, but predictably many exceptions exist The oxidation of the potassium salts of perfluoro acids with potassium persulfate leads to decarboxylation and coupling [93] (equation 59)... 

The reaction fails if the decarboxylation produces a radical that is easily oxidized, such as an a-hydroxyalkyl radical.2 In intermediate cases, such as tert-alkyl or a-alkoxyalkyl radicals,2 the yield based on the parent quinono is usually improved by using an excess of persulfate and carboxylic acid to compensate for the loss of radicals due to oxidation (footnote b, Table I). 

Minisci-type substitution is one of the most useful reactions for the synthesis of alkyl- and acyl-substituted heteroaromatics. The acyl radicals are formed by the redox decomposition from aldehyde and /-butyl hydroperoxide or by silver-catalyzed decarboxylation of a a-keto acid with persulfate. Synthesis of acylpyrazines 70 as ant pheromones are achieved by this methodology using trialkyl-substituted pyrazines 69 with the acyl radicals generated from aldehydes or a-keto acids (Equation 10) <1996J(P1)2345>. The latter radicals are highly effective for the acylation. Homolytic alkylation of 6-chloro-2-cyanopyrazine 71 is performed by silver-catalyzed decarboxylation of alkanoic acids to provide 5-alkyl-substituted pyrazines 72 (Scheme 18) <1996CCC1109>. 

The persulfate ion S2OI-, with or without various transition metal ions, is a particularly effective oxidant, especially for the decarboxylation of carboxylic acids.535 In the presence of silver(I), persulfate oxidation to silver(II) readily occurs and for aliphatic carboxylic acids the decarboxylation mechanism given in Scheme 4 has been established. The aliphatic radicals produced may then disproportionate, abstract hydrogen or be further oxidized to an alcohol. In... 

Another example is represented by the oxidative decarboxylation of oc-ketoacids in the presence of the S2082 /Ag+ redox system, which leads to the formation of acyl radicals by means of the intermediate Ag2+ (Equations 14.5 and 14.6) [10]. In this case, the re-aromatization of the ring can occur according to two parallel paths oxidation by persulfate (Scheme 14.1a) and by Ag(II) (Scheme 14.1b). Thus, this system needs more than the stoichiometric quantity of persulfate, as it both reacts... 

Generally, potassium persulfate in the presence of Ag+ is used for the Hunsdiecker type radical decarboxylation of carboxylic acids in water. (Bu4N+)2S208 (P) is soluble in THF, and a sulfate anion radical [i] is formed under refluxing conditions. Thus, refluxing treatment of / (tetrabutylammonium) persulfate (P) in the presence of alcohol in THF provides tetrahydrofuryl-protected alcohol (4), through the abstraction of a-H from THF by sulfate anion radical [I], followed by oxidation to a tetrahydrofuryl cation, as shown in eq.12.3 [28]. 

In an approach to direct C-functionalization of triazolo[4,5-c]pyridines, shown in Scheme 3, 1-methyl (or phenyl)[l,2,3]triazolo[4,5-c]pyridines (26,33) are alkylated exclusively at C-4 by radicals generated by decarboxylation of carboxylic acids (ammonium persulfate-sulfuric acid-silver nitrate) <90ZOB683>. However, with /-butanol various products are obtained depending on the catalyst employed. For example, with ammonium persulfate-sulfuric acid-silver nitrate, exclusive C(4)-methylation (34) was observed, while ammonium persulfate-sulfuric acid gave exclusively C(4)-/ -hydroxy-/ ,/ -dimethylethylation (cf. (36)). The /-butyl analogue (35) was obtained by decarboxylation of pivalic acid. 

The oxidative decarboxylation of aliphatic carboxylic acids is best achieved by treatment of the acid with LTA in benzene, in the presence of a catalytic amount of copper(II) acetate. The latter serves to trap the radical intermediate and so bring about elimination, possibly through a six-membered transition state. Primary carboxylic acids lead to terminal alkenes, indicating that carbocations are probably not involved. The reaction has been reviewed. The synthesis of an optically pure derivative of L-vinylglycine from L-aspartic acid (equation 14) is illustrative. The same transformation has also been effected with sodium persulfate and catalytic quantities of silver nitrate and copper(II) sulfate, and with the combination of iodosylbenzene diacetate and copper(II) acetate. ... 

A key step in the synthesis of the simple aromatic bisphenol tetrangulol (3) by Brown and Thomson [18] was a Michael-type cyclization of a phenol to the chloronaphthoquinone moiety (Scheme 3). The starting material 8, connecting the naphthoquinone and the protected phenol, was prepared by an interesting radical alkylation of the chloronaphthoquinone 6 with a carboxylic acid 7 in the presence of silver ions and persulfate with concomitant decarboxylation (Torsell reaction [19]) to yield the dihydrobenzo[a]anthraquinone 9. The synthesis of tetrangulol (3) was concluded by dehydrogenation in boiling nitrobenzene. 

In another nonelectrolytic process, aryl acetic acids are converted to vic-diaryl com-ponnds 2ArCR2COOH ArCRaCRaAr by treatment with sodinm persulfate Na2S20g and a catalytic amormt of AgN03-" Photolysis of carboxylic acids in the presence of Hg2p2 leads to the dimeric alkane via decarboxylation. Both of these reactions involve dimerization of free radicals. In still another process, electron-deficient aromatic acyl chlorides are dimerized to biaryls (2 ArCOCl Ar—Ar) by treatment with a disUane R3SiSiR3 and a palladium catalyst. ... 

Oxidative decarboxylation. Fichter et al.1 some time ago studied the decarboxylation of salts of carboxylic acids by persulfate ion. Kochi2 now finds that... 

OXIDATIVE DECARBOXYLATION Lead tetraacetate. Potassium persulfate. 

Potassium persulfate sodium hydroxide Decarboxylative ring closure... 

Generation of tert-Butyl Radicals via Oxidative Decarboxylation. Silver-catalyzed decarboxylation of carboxylic acids by persulfate generates alkyl radicals, which have been used for ho-molytic alkylation of aromatic bases. Pivalic acid is a source of f-butyl radicals in this process. 2-f-Butylquinoline is formed re-gioselectively by this method (eq 3) 6-r-butylnicotine has been prepared in a similar way. ... 

Synthesis of compound 68 by oxidative decarboxylation of adamantane carboxylic acid is described in [25], Initially, for the synthesis of 2-(l-adamantyl)benzimidazole (68), adamantan radical was obtained in sulphuric acid diluted by silver nitrate in the presence of ammonia persulfate. Then, the synthesized radical was inserted directly into the heterocycle. After N-methylation, 2-(l-adamantyl)benzimidazole (68) was transferred in l-methyl-2-(l-adamantyl)-benzimidazole (79). The experiments carried out on chicken embryo revealed high antiviral activity of both obtained compounds [25] ... 

In 1984, Tsupak and co.[64] synthesized 2-(l-adamantyl)benzimidazole (68) with 45% yield by substitution of sulpho group in benzimidazole-2-sulfonic acid with adamantly radical. The reaction was carried out in aqua acetonitrile solution. The adamantyl radical was obtained by oxidativ decarboxylation of adamantanecarboxylic acid with ammonia persulfate in silver nitrate aqua solution. 

The majority of examples of metal-assisted hydrolysis of peptides which have been reported recently involve the use of cobalt(II) centers. However, use of copper(II) for the specific hydrolysis of the C-terminal residue of polypeptides has been reported. The polypeptides coordinate to the copper with concomitant deprotonation of the amido group of the C-terminal residue. Treatment with persulfate results in an oxidative decarboxylation to yield an iV-acylimine, which undergoes subsequent hydrolysis to generate a carbonyl compound and carboxamide. This results in an overall process, Eq. (3). In contrast, treatment with [IrCl ] results in the alternative reaction (4), although this process is dependent upon the redox potential of the copp r(II)/copper(III) couple. 

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