Nitro acids, decarboxylation

Here too there is an enol that tautomerizes to the product. The mechanism is illustrated for the case of P-keto acids, ° but it is likely that malonic acids, a-cyano acids, a-nitro acids, and P,y-unsaturated acids behave similarly, since similar six-membered transition states can be written for them. Some a,P-unsaturated acids are also decarboxylated by this mechanism by isomerizing to the p,y-isomers before... 

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... 

An earlier series of experiments established useful synthetic transformations involving carboxylation of ketones and nitroalkanes to yield P-keto acids and a-nitro acids respectively (Scheme 94).362 363 The reagent is methylmagnesium carbonate and the intermediate (130) can be alkylated with concomitant decarboxylation to provide greater versatility. These reactions can also be extended to ketone functions in imidazoline- and oxazolidine-diones (Scheme 95).364,365... 

Other decarboxylations are noteworthy. Thermal decomposition of 2,4,6-trinitrobenzoic acid furnishes 1,3,5-trinitrobenzene in 46% yield. In an adaptation of a procedure for the decarboxylation of halogenated furoic acids with boiling quinoline and powdered copper, 2- and 3-nitro-benzofuran are prepared from nitro acids and 5-nitrothionaphthene is formed from the corresponding 2-carboxylic acid. ... 

The data for this solvent were not used to calculate the parameters in Table 54. Similarly the data for decarboxylation of oxanilic acid in anisole were not used for the AH -AS correlation. With the reported AH value of 32.6 kcal.mole , the entropy of activation is calculated to be 3.59 0.03 eu compared to the reported value of 11.1 eu. In the decarboxylation of malonic acid, the data obtained with pyridine and ) -mercaptopropionic acid solvents deviated considerably from the plots and were not included in the correlation. The data for malonic acid decarboxylation appeared to be best correlated by two lines. One line was described by the following solvents acids, phenols, nitro-aromatics, benzaldehyde, and the melt the other line involved amines, alcohols, dimethylsulfoxide and triethyl phosphate. The latter line was not as well defined as the former. However, it was our intention to correlate as many solvents as possible with a minimum number of lines. The data for decarboxylation of malonic acid in water and in benzyl alcohol fell between these two lines and were not included in either correlation. The data for decarboxylation of benzylmalonic acid also appeared to be best correlated with two lines. One line was defined by the cresols, acids and the melt, while the other line was defined by the amines. Decarboxylation of cinnamalmalonic acid was correlated by two lines as indicated in Table 54. Similarly j8-resorcylic acid was correlated by two lines. The separation of data into parallel lines is presumably due to multiple solvation mechanisms . In support of this interpretation it is seen that when two lines are observed, acids fall into one line and amines into the other. It is not unexpected that the solvation mechanisms for these two classes of solvents would differ. It is interesting to note that all of the nitrogen containing acids are correlated reasonably well with one line for both basic and acidic solvents. Also the AHq values fall in a rather narrow range for all of the acids. From the values of p in Table 54, there appears to be little correlation between this parameter and the melting point of the acids, contrary to prior reports " ... 

Falconer JL, Madix RJ (1974) The kinetics and mechanism of the autocatalytic decomposition of HCOOH on clean Ni(llO). Surface Sci 46 473-504 Finkbeiner HL, Stiles M (1963) Chelation as a driving force in organic reactions. a-Nitro acids by control of the carboxylation-decarboxylation equilibrium. J Am Chem Soc 85 616-622... 

Cydopentane reagents used in synthesis are usually derived from cyclopentanone (R.A. Ellison, 1973). Classically they are made by base-catalyzed intramolecular aldol or ester condensations (see also p. 55). An important example is 2-methylcydopentane-l,3-dione. It is synthesized by intramolecular acylation of diethyl propionylsucdnate dianion followed by saponification and decarboxylation. This cyclization only worked with potassium t-butoxide in boiling xylene (R. Bucourt, 1965). Faster routes to this diketone start with succinic acid or its anhydride. A Friedel-Crafts acylation with 2-acetoxy-2-butene in nitrobenzene or with pro-pionyl chloride in nitromethane leads to acylated adducts, which are deacylated in aqueous acids (V.J. Grenda, 1967 L.E. Schick, 1969). A new promising route to substituted cyclopent-2-enones makes use of intermediate 5-nitro-l,3-diones (D. Seebach, 1977). 

The intermediacy of an aci-nitro compound has been proposed for the sulfuric acid cyclization of o-nitrophenylacetic acid to yield a mixture of 2,1-benzisoxazole and 2,1-benzisoxazole-3-carboxylic acid. The acid does not decarboxylate under the reaction conditions. The proposed aci-nitro intermediate cyclized to an A/ -hydroxy compound which decomposed to the products (Scheme 179) (70JCS(C)2660). 

Selenophene-2-carboxylic acid, 4-nitro-decarboxylation, 4, 947, 952 Selenophene-2-carboxylic acid, 5-nitro-decarboxylation, 4, 947, 952 Selenophenecarboxylic acids, acidity, 4, 71... 

Finally, certain 3-substituted compounds can be prepared by utilizing the - meta) directing powet (cf. Section IV,B) of some groups in the 2-position which afterward can be removed. 3-Nitrothiophene is prepared by nitration of 2-thiophenesulfonyl chloride and by removal of the sulfonic acid group of the 4-nitro-2-sulfonyl chloride formed with superheated steam. Another approach to 3-nitrothio-phene is to nitrate 2-cyanothiophene, separate the 4-nitro-2-cyano-thiophene from the 5-isomer, hydrolyze, and decarboxylate. A final method of preparation of 3-nitrothiophene is by simultaneous de-bromination and decarboxylation of 5-bromo-4-nitro-2-thiophene-carboxylic acid obtained through the nitration of methyl 5-bromo-2-thiophenecarboxylate. 

The quindoline 224 may be prepared by the condensation of indoxyl-2-carboxylic acid with 6-aminopiperonaldehyde in the presence of hydrochloric acid, when decarboxylation and cyclization take place. Nitric acid oxidation of 224 gave an unstable nitrodicarboxylic acid which decarboxylated readily to a nitromonocarboxylic acid formulated as 8-nitro-8-carboline-3-carboxylic acid (225). ... 

ETHYL BENZOATE VIA THE NITRO-SOAMIDE DECOMPOSITION, 47, 44 Decachlorobi-2,4-cyclopentadienyl, dechlorination by triisopropyl phosphite, 46, 93 a-Decalones, 46, 82 Decanoyl fluoride, 46, 6 Decarboxylation, in formation of couma-rone from o-formylphenoxyacetic acid, 46, 28... 

Diazotization of the amines 1, obtained by catalytic hydrogenation of the corresponding nitro compounds, gives the esters 2 directly. Alkaline hydrolysis of the latter yields the acids 3, which can be decarboxylated to l//-l,2,5-benzotriazepin-4(5/7)-ones 4. Yields were not reported.372... 

Amino-5-imidazole carboxylic acid (38) has been synthesized from 4-nitro-5-imidazole carboxylic acid by catalytic hydrogenation and shown [56JBC(218)175] to spontaneously decarboxylate at low pH to give 4-aminoimidazole (39). 

Nitro-2-methylpyridine was obtained in 87% yield when diethyl malo-nate was reacted with 5-nitro-2-chloropyridine in DMF in the presence of sodium hydroxide at room temperature, and the diethyl (5-nitro-2-pyridyl)malonate was then hydrolyzed and decarboxylated by heating in dilute hydrochloric acid at reflux temperature (88GEP3707361, 88GEP3708093). 

N-(4-nitrophenyl)-amino acids N-(2,4-dinitrophenyl)-amino acids 8) and 3-nitro-2-pyridyl amino acids have been of considerable interest. A generally applicable mechanistic scheme does not exist so far, and except for 3-nitrophenyl acetate in ortho and/or -para position of the phenyl (pyridyl) ring seems to be a prerequisite for efficient decarboxylation. 

Photodecarboxylation of similar but nitro group free substrates have also been verified, however. N-2-chlorophenylglycine and (although less efficient) a-phenylthio-acetic acid have been decarboxylated by irradiation in acetonitrile solution in the presence of 1-nitronaphthalene, 4-nitro-biphenyl, 1,4-dinitrobenzene, 4-nitrotoluene and nitrobenzene... 

It is assumed that an excited state charge transfer complex is formed between the nitroaromatic in its first triplet state and the respective substrate. Internal proton transfer is immediately followed by hberation of carbon dioxide. Finally hydrolysis of the hemiacetal Ar —X—CH2OH (X = NH or S) leads to 2-chloro-aniline or thiophenol, respectively. In the decarboxylation of a-phenylthio-acetic acid, some methyl-phenylsulfide is also formed. (7t,7r )-nitroaromatics are more reactive than nitro compounds with lowest (n,7t )-triplets iso). 

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