Pyrrole-2-carboxylate esters

Other Methods. Newer methods for forming pyrrole and related heterocyctic rings iaclude the formatioa of substituted pyrrole 2-carboxylate esters by coadeasatioa of P-dicarboayl compouads with glyciaate esters (25). 

Predictably, nitrosation of 2-acetylpyrrole and pyrrole-2-carboxylic esters with alkyl nitrites or nitrous acid preferentially yields the relatively stable 4-nitroso derivatives, whilst 2,4-dialkyl- or -diaryl-pyrroles are nitrosated at the 5-position. Further reaction of the dialkyl and diaryl nitrosopyrroles with an excess of alkyl nitrite in the absence of a base can result in the formation of the nitropyrroles, whereas the reaction with nitrous acid converts the nitrosopyrroles into diazopyrroles (B-77MI30502). 

Several new examples of the Barton-Zard pyrrole synthesis from nitroalkenes and isocyanoacetate esters demonstrate the broad utility of this procedure. An excellent yield of ethyl 3-(9-anthryl)-4-ethylpyrrole-2-carboxylate was obtained starting with the nitroalkene from anthracene-9-carboxaldehyde and 1-nitropropane. <95TL8457> Bums et.al. reported an improved synthesis of benzyl isocyanoacetate which facilitates the synthesis of benzyl pyrrole-2-carboxylate esters by this method. <95SC379> 3-(l-Arylpyrrol-2-yl)pyrrole-2-carboxylates were prepared from l-aryl-2-(nitrovinyl)pyrroles. <95JHC 1703>... 

The total synthesis of manzacidin, a pyrrole-2-carboxylate ester with a dihydropyrimidine side chain, was achieved <04TL7197>. As mentioned previously, the total syntheses of the pyrrole-2-carbinol natural products, funebrine 11 and funebral, were disclosed <04JOC1475>. 

A practical synthesis of polysubstituted pyrrole-2-carboxylic esters is via the corresponding benzyl esters, the other functional groups are not affected under hydrogenolysis conditions. ... 

DBU is capable of inducing the elimination of /3-acetoxy nitroalkanes and deprotonation of benzyl isocyanoacetate. A tandem Michael-Henry reaction of the resulting species ensues, leading to 3,4-disubstituted pyrrole-2-carboxylic esters. 

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. 

Substituted pyrrole-2-carboxylic esters 53 are synthesized from N-tolylsulfonyl glycine ester 51 and vinyl ketones (Kenner synthesis) [117]. 

Scheme 66 Pyrrolo[l,2-a]quinoxaline formation via CuI/L-proline catalyzed coupling of 2-halotrifluoroacetanilides and pyrrole-2-carboxylate esters...

CuI/L-proline-catalyzed coupling of 2-halotrifluoroacetanilides 187 with pyrrole-2-carboxylate esters 188 in dimethyl sulfoxide (DMSO) at 80-90°C followed by in situ hydrolysis and condensative cyclization at60°C affordedpyrrolo[l,2-a]quinoxalines 189 with good yields (Scheme 66) [111]. Indole-2-carboxylate esters underwent the same process smoothly to provide the corresponding tetracychc products. 

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