Pyrrole-2,3-dicarboxylic acid

Oxidation of sepiomelanin with potassium permanganate gave four pyrrolic acids, pyrrole-2,3,5- and 2,3,4-tricarboxylic acid, pyrrole-2,3-dicarboxylic acid (PDCA), and 2,3,4,5-pyrroletetracarboxylic acid (184, 204). On the other hand, the yield and number of PDCA increased when decarboxylated sepiomelanin was oxidized with permanganate. The origin of these pyrrolic acids was interpreted as resulting from the oxidative breakdown of various types of DHI units in the pigment backbone (184). 

Thermally Stable Polyimides from Pyrrole Dicarboxylic Acid Anhydride Monomers... 

Arylene-bis-(pyrrole dicarboxylic acid anhydrides) were prepared by the condensation of two moles of diethyl diacetyl succinate with one mole of aromatic diamine, followed by hydrolysis and dehydration. Condensation of these novel dianhydrides with various aromatic diamines resulted in the formation of poly (amic acids) which were further condensed to polyimides. If the diethyl diacetyl succinate and aromatic diamine were reacted in equimolar quantities an N-(amino aryl) pyrrole diester was formed which can be further condensed to give polyimide directly. 

Figure 5 Proposed mass spectral fragmentations of pyrrole dicarboxylic acids.

To 5a] In view of the behaviour of esters of pyrrole-dicarboxylic acids, already reported, it is interesting to notice that methyl pyrrole-2-carboxy-late undergoes alkaline hydrolysis considerably faster than the 3-isomer [10 A 2 (1. mole i sec ) (25°), 231, 4 1 and 0 59, for ethyl pyrrole-1-, and methyl pyrrole-2- and -3-carboxylate, respectively, in 56 per cent aqueous acetone]. The effect is attributed to intramolecular hydrogen bonding in the transition state (109)374 (cf. to c above). 

Pyrrole-2,3-dialdehyde, 1-methyl-pyrrolopyridazine synthesis from, 4, 517 Pyrrole-2,5-dicarboxylic acid, 3,4-dihydroxy-l-phenyl-diethyl ester... 

Pyrrole-3,5-dicarboxylic acid, 1-aryl-2-hydroxy-diethyl ester synthesis, 4, 123... 

Bis(3,4-diethyl-2-pyrrolylmethyl)-3,4-dietliyl-l//-pyrrole (2), prepared in situ from the di-t-butylester of the 5,5 -dicarboxylic acid (/), reacts with 4//-1,2,4-triazole-3,5-dialdehyde (3) in di-chloromethane in the presence of trifluoroacetic acid and 2,3-dichloro-5,6-dicyano-/)-benzoquino-ne as an oxidation reagent. Dark blue crystals are obtained after chromatographic purification. The dark violet chloroform solution fluoresces purple at 360 nm and gives the NMR experiments 39. Which compound and which tautomer of it has been formed ... 

Pyrrole is one of the most prominent heterocycles, having been known for more than 150 years, and it is the structural skeleton of several natural products, synthetic pharmaceuticals, and electrically conducting materials. A simple access to the pyrrole ring system involves the conversion of cyclic anhydrides into five-membered imides. Mortoni and coworkers have described the conversion of 2-methylquinoline-3,4-dicarboxylic acid anhydride to a quinoline-3,4-dicarboximide library by treatment of the anhydride with a diverse set of primary amines under microwave conditions (Scheme 6.180) [341]. The authors studied a range of different conditions, including dry media protocols (see Section 4.1) whereby the starting materials were adsorbed onto an inorganic support and then irradiated with microwaves. For the transforma-... 

By 2D TOCSY NMR spectroscopy (TOCSY - total correlated spectroscopy), the structure of a biosynthetic intermediate of PQQ was shown to be 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid 15, not its constitutional isomer 16 <2004JA3452>. This result shows that the last enzyme on the biosynthetic pathway of PQQ facilitates a pyrrole ring closure and an unprecedented eight-electron oxidation of 15. 

This synthetic route is based on ring closure by Dieckmann condensation of 1,2-bis-carbalkoxyalkylpyrrolidines. It has gained special importance during the last few years, after application to several total syntheses of naturally occurring pyrrol izidine bases. The usual starting compounds employed in this route are esters of a-pyrrolidineacetic acid, proline, and their homologues, which are converted into N-substituted dialkyl dicarboxylates. The esters of the dicarboxylic acids are subjected to Dieckmann condensation and subsequent ketonic hydrolysis the resultant ketones are used in further reactions. 

Pyrroles are obtained by reduction of 1,2-diazines (80JMC481). This reaction has been used in conjunction with inverse electron demand Diels-Alder reactions to prepare 3,4-disubstituted pyrrole-2, 5-dicarboxylic acid derivatives(Scheme 67). Silyl enol ethers or enamines can also serve as the electron-rich dienophiles thus, silyl ethers of ester enolates give 3-methoxypyrroles (84JOC4405). 

While dicarboxylic acid-functional pyrroles have received only cursory attention in condensation polymerizations, other derivatives have been studied extensively. Pyrrole itself has been electrooxidatively polymerized (81CS145) to give a flexible conductive film, presumably containing poly(2,5-pyrrolediyl) units (23) as the main structural feature. The blue-black polymer obviously contains other functionality, as evidenced by elemental analysis and by the fact that it carries a partial positive charge, and it exhibits p-type conductivities approaching the metallic range (e.g. 100 fi-1 cm-1). The main utility of poly(pyrrole) (23) has been for the modification of electrode surfaces, although numerous other applications can be envisioned. 

Pyrrole- and indole-carboxylic acid chlorides react with dialkyl- and diaryl-cadmium to yield the ketones and it is noteworthy that the reaction of the anhydride of indole-2,3-dicarboxylic acid with diphenylcadmium produces 3-benzoylindole-2-carboxylic acid and not its isomer (53JCS1889). The ability of l-methylindole-2-carboxylic acid to react with nucleophiles is enhanced by conversion into the mixed anhydride with methanesulfonic acid. The mixed anhydride reacts with carbanions derived from diethyl malonate and from methyl acetate to yield the indolyl (3- keto esters (80TL1957). 

Permanganate oxidation of porphyrins yields pyrrole-2,5-dicarboxylic acids (Scheme 5), which can be readily identified by paper chromatography. This method for structure... 

Decarboxylation of this dicarboxylic acid gave almost quantitavily the disered 3-chloro-4-(2 -nitro-3 -chlorophenyl)pyrrole MP 125°C. (recrystallized from benzene). 

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