Reductive C -alkylation

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When porphyrins or related pigments are reduced by HI-AcOH, their meso-substituents (R = H or alkyl) appear as a-CH2R groups in the resulting pyrroles. The identification of the pyrroles, as by g.l.p.c., defines and orders the meso-substituents flanking each pair of peripheral substituents in the porphyrin. If one meso-substituent differs from the others, all the substituents about the two adjacent pyrrole nuclei are then ordered.The pyrroles can be reductively alkylated in situ, and symmetry then reduces their number when the aldehyde used (R.CH0) corresponds to a bridge and its meso-substituent. This may simplify the pyrrole mixtures, identify meso-substituents, or make pyrroles distinguishable by g.1.p.c.The critical pyrrole -propionic acids are separable as methyl esters by g.1.p.c. Desoxophylloerythrin and pyrophaeophorbides (the latter first reduced with potassium borohydride) are reduced to cyclopenteno-pyrroles which reveal the isocyclic rings and the 5-substituents. The r.r.t.3 of relevant pyrroles are reported.La reduction des porphyrines et des pigments du mCme genre par HI-AcOH fait que les substituants mtso (R = H OLI alkyle) apparaissent sous forme de groupements CH2R en cc des pyrroles resultants. L'identification des pyrroles par c.p.l.g., par exemple, definit et classe les substituants meso qui se trouvent a cBte de chaque paire de substituants peripheriques dans la porphyrine. Si un des substituants meso differe des autres, tous les substituants autour des deux noyaux pyrroles adjacents sont alors clasds.L'alkylation reductive irz situ des pyrroles peut riduire par symitrie le nombre de pyrroles lorsque l'aldehyde utilise (R.CH0) correspond au pont et au substituant meso de la porphyrine initiale. Ceci peut simplifier le melange des pyrroles, identifier les substituant meso et differentier les pyrroles par c.p.1.g.Les acides critiques pyrrole -propioniques sont separables de leurs esters methyliques par c.p.1.g. La dCsoxophylloerythrine et les pyrophaephorbides (ces dernieres d'abord reduites par le borohydrure de potassium) sont reduites en cyclopenteno-pyrroles, ce qui revele les noyaux isocycliques et les substituants en 5. Les donnees t.r.r, des pyrroles correspondants sont rapportkes.

mentioning

confidence: 99%

The Analytical Reduction of Porphyrins to Pyrroles

Chapman¹,

Roomi²,

Morton³

et al. 1971

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“…Tetramethylpyrrole (2.1) had been obtained from 2,4-dimethylpyrrole (1) and from some of its derivatives with paraformaldehyde and hydriodic acid at 100" (1). It has now been obtained in the same way from 2,3-dimethylpyrrole (2) from 2,5-dimethylpyrrole (3), from 10, and from 13.…”

Section: Introductionmentioning

confidence: 97%

“…Hydriodic acid was ineffective there and, in one case at least, gave the 3-(1-iodo-alkyl) derivative (1). There is no evidence that the zinc method is preferable in any other circumstances.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Reductive C-alkylation. II

Roomi¹,

MacDonald²

1970

Self Cite

102

Methylpyrrole carboxylic esters generally are reductively methylated at 25-45', Some are also reductively alkylated by aliphatic aldehydes generally to give, for example, 2,3(or 2,4)-dimethyl-4(or 3)-alkyl-5-carbethoxypyrroles, using hydriodic acid or HCl/AcOH-Zn/Hg respectively. An analogous alkylation by glyoxylic acid gave 5-carbethoxyhemopyrrole-dicarboxylic ester. Using HI, paraldehyde at 100" gave diethyl derivatives of dimethylpyrroles, and an~inoacetal at 35' converted 2,4-dimethyl-3-acetylpyrrole into its 5-(2-amino-ethyl)-derivative. Reductive alkylations have been most useful with pyrroles but HI converted 2-biphenylcarbaldehyde into Auorene.

“…Results and Discussion During the course of work on the Hantzsch synthesiswand the alkylation of pyrroles, a large number of alkyl pyrroles and their carboxylic esters have been prepared (1,2). Very little work has been reported-on the nuclear magnetic resonance (n.m.r.)…”

Section: Introductionmentioning

confidence: 99%

Nuclear magnetic resonance study of carbethoxypyrroles

Roomi¹,

Dugas²

1970

The chemical shifts and the ring proton coupling constants of various substituted carbethoxypyrroles are reported.The electron-withdrawing effect of the carbethoxy groups shifts the resonances of the ring substituents to low field while the inductive and mesomeric effects of the methyl groups shift the resonances to higher field. The deshielding effect is more pronounced with 2-carbethoxypyrroles than for 3-carbethoxypyrroles. The ring proton spin-spin coupling constants depend on the nature of substituents and increase with the electronegativity of the substituents. In some cases long-range coupling between the methyl side-chain protons and ring protons could be observed.Canadian Journal of Chemistry, 48, 2303 (1970) IntroductionResults and Discussion During the course of work on the Hantzsch synthesiswand the alkylation of pyrroles, a large number of alkyl pyrroles and their carboxylic esters have been prepared (1,2). Very little work has been reported-on the nuclear magnetic resonance (n.m.r.) analysis of substituted pyrroles (4)(5)(6)(7)(8)(9) and only few carbethoxypyrroles have been analyzed (7). It is the purpose of this paper to present a systematic analysis of the n.m.r. spectra of some substituted carbethoxypyrroles and also to investigate the effect of substitution on the chemical shifts and the magnitude of the spinspin coupling constants between the ring protons in these molecules.