Pyrrole-2-carboxylic acid esters, from ketone

Pyrrole-2-carboxylic acid esters, from pyrrol-2-yl trichloromethyl ketone, 51, 102 PYRROLE—2-CARBOXYLIC ACID,... 

Nearly 1000 compounds have so far been identified in the volatile constituents of meat from beef, chicken, mutton and pork (6). The largest number of volatiles has been determined in beef and these were representative of most classes of organic compounds. Hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, esters, lactones, ethers, sulfur and halogenated compounds as well as different classes of heterocyclic substances (Figure 1) namely furans, pyrldlnes, pyrazines, pyrroles, oxazol(in)es, thiazol(in)es, thiophenes were present in cooked meat flavor volatiles as shown in Table I. Many of these compounds are unimportant to the flavor of meat and some may have been artifacts (16). 

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). 

Pyrrole aldehydes and ketones are important sources of alkylpyrroles, formed from them by WolfF-Kishner reduction 232 -3, 33i, More recently, lithium aluminium hydride has been used for this purpose32 233, 332 -5 Direct addition of the carbonyl compound to the reagent gives the alkyl-pyrrole, whilst inverse addition allows preparation of the carbinol. Carboxylic acids and their esters are also reduced by lithium aluminium hydride to alkylpyrroles. In contrast to pyrrole aldehydes unsubstituted at nitrogen, 2-and 3-formyl-1-methylpyrroles are reduced by lithium aluminium hydride only to the carbinol stage sa. The difference is explained by the mechanism... 

Substituted pyrrole-2-carboxylic esters 19 are synthesized from A-tolylsulfonyl glycine ester 17 and vinyl ketones Kenner synthesis) [42]. By Michael addition and intramolecular aldol addition, they first yield pyrrolidine-2-carboxylic esters 18. These are converted into pyrroles by succesive H2O and sulfmic acid eliminations. 

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