Acidity continued pyrrole

Lanthanide based Lewis acids continue to play pivotal roles in expediting electrophilic substitution reactions of both pyrroles and indoles vide infra). To the point, pyrroles (e.g., 63) have been found to undergo efficient conjugate addition with electron deficient olefins 66 in the presence of a catalytic amount of indium trichloride to afford the Michael adducts 67 <01TL8063>. 

Reviews dealing with a specific reaction or property from the heterocyclic point of view have been rarer—tautomerism (continued from Volume 1), free radical substitution, metal catalysts and pyri-dines, acid-catalyzed polymerization of pyrroles, and diazomethane reactions have been covered in this volume. 

Due to the biological significance of some azoles (pyrrole, indole, imidazole, benzimidazole) and the consequences of acid-base equilibria in their functions, a continuous interest in the behavior in water is to be expected. To quote a significant approach, imidazole is being used to determine the intra- and extracellular acidity by H-NMR (82MI4 86UP13). 

Here, the parallels with benzenoid counterparts continue, for these compounds have no special properties - their reactivities are those typical of benzenoid aldehydes, ketones, acids and esters. For example, in contrast to the easy decarboxylation of a-acids observed for pyrrole and furan, thiophene-2-acids do not easily lose carbon dioxide nevertheless, high-temperatme decarboxylations are of preparative value (see also 17.12.1.2). "... 

A microemulsion polymerization method [62,63] was also reported to produce magnetic polypyrrole nanocomposites filled with 7-Fc203. The nanoparticles were dispersed in the oil phase. FeCla was used as an oxidizing agent. Sodium dodecylbenzenesulfonic acid (SDBA) and butanol were used as the surfactant and cosurfactant, respectively. FeCl3 (0.97 g) was dissolved in a mixture of 15 mol deionized water, SDBA (6 g), and butanol (1.6 ml). A specific amount of 7-Fc203 suspended nanoparticle solution was added to the above solution for dispersion. Pyrrole was added for nanocomposite polymer fabrication in the microemulsion system. The polymerization was continued for 24 hours and quenched by acetone. 

N-(3,5-Diethoxycarbonyl -4-methylpyrrol -2-ylmethyl)-N-methanesulfonyl -o-phen-ylenediamine dissolved in acetic acid, coned. HCl added, cooled to 0-5°, aq. NaNOg added dropwise, stirring continued 0.5 hr. in the ice-bath, cuprous oxide added, the ice-bath removed, and stirred 15 min. spiro[l-methanesulfonyl-3H-indoline-3,2 -(3, 5 -diethoxycarbonyl-4 -methyl-2 H-pyrrole] (Y 90%)... 

An equimolar mixture of dibenzyl ketone, methylhydrazine, and anhydrous xylene stirred 3-4 hrs. at room temp, in the presence of a trace of p-toluene-sulfonic acid, then refluxed ca. 0.5 hr. with azeotropic removal of the resulting water, an additional mole of dibenzyl ketone added, and refluxed 1 week with continued removal of the resulting water 2,5-dibenzyl-l-methyl-3,4-diphenyl-pyrrole. Y 15%. F. e., also unsym. pyrroles with 2 different ketones, s. J.-P. Chapelle et al., Bl. 1971, 280. 

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