The 2H- and 3H-Pyrroles

Sammes, M. P.; Katritzky, Alan R.

doi:10.1016/s0065-2725(08)60655-8

Cited by 32 publications

(10 citation statements)

References 128 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1,2 and 1,4 H-atom migrations in pyrrolenine lead to different isomerization products. Whereas the existence of pyrrolenine was never established experimentally (only substituted of pyrrolenines are known − ), quantum chemical calculations can shed light on its function as an intermediate species in the thermal isomerizations of pyrrole. Both Lifshitz et al and Mackie et al suggested that only two isomerization products, cis -crotonitrile and vinylacetonitrile, are formed in the isomerization of pyrrole and that trans -crotonitrile is formed by the cis → trans isomerization of the cis isomer.…”

Section: Introductionmentioning

confidence: 99%

Isomerization of Pyrrole. Quantum Chemical Calculations and Kinetic Modeling

Dubnikova

Lifshitz

1998

J. Phys. Chem. A

View full text Add to dashboard Cite

Density functional theory (DFT) calculations including configuration interaction (CI) were carried out to investigate the pathways of the unimolecular isomerizations of pyrrole. Vibrational frequencies calculated with the DFT method were used to estimate transition-state theory frequency factors. The potentional energy surface of the overall isomerization of pyrrole is composed of pyrrolenine, two biradical intermediates, and five transition states, in addition to pyrrole and its stable isomers. The first step of the isomerization is a fast transition from pyrrole to pyrrolenine. These two species reach a state of equilibrium that is maintained during the entire process. There is no direct path that leads from pyrrole to its stable isomers, which are produced only from pyrrolenine. Two biradical intermediates that are very similar in their structure and energetics and that isomerize to one another by a low-barrier rotation are involved in the process of pyrrole isomerization. One intermediate forms only cis-crotonitrile, and the other intermediate forms only vinylacetonitrile. These two biradical intermediates and several transition states have resonance structures. There is no direct route that leads from pyrrolenine to trans-crotonitrile. The latter is formed from the cis isomer by cis → trans isomerization. RRKM calculations were carried out to transfer values of A ∞ and E ∞ of the rate constants of two high-barrier steps in the isomerizations to A and E corresponding to the experimental conditions. Kinetic modeling, which uses the calculated rate constants, gives a very good agreement between the calculated and the experimental yields of the isomerization products.

show abstract

Section: Introductionmentioning

confidence: 99%

Isomerization of Pyrrole. Quantum Chemical Calculations and Kinetic Modeling

Dubnikova

Lifshitz

1998

J. Phys. Chem. A

View full text Add to dashboard Cite

show abstract

“…From our previous results,' a limited order of relative migratory aptitudes (MeS or PhS > C02Et, CHO, or COMe) had already been established, but clearly it was necessary to investigate a wider range of substituents. Therefore the starting materials chosen were the azides (8) and (9 Two series of compounds were studied; the thiophenes (8) which give thieno [3,[2][3][4][5][6]pyrroles on irradiation, and the corresponding benzo compounds (9) which lead to indoles, although most of the work was done in the thiophene series.…”

Section: Resultsmentioning

confidence: 99%

“…Since the non-aromatic fused 2H-pyrrole intermediate (3) proposed in the rearrangement of the thiazine (1) (Scheme 1) is isoelectronic with the 2H-indene intermediate (6) in the rearrangement of 1H-indenes (Scheme 2), we have now investigated a wider range of substituents in the thiazine series in order to establish the relative order of migratory aptitudes and, in particular, where sulphur substituents fall in this order.…”

mentioning

confidence: 99%

Photochemical conversion of 3-azido-2-vinylthiophenes into thienopyrroles and of 2-azidostyrenes into indoles. High migratory aptitude of sulphur substituents

Gairns¹,

Moody²,

Rees³

1986

J. Chem. Soc., Perkin Trans. 1

View full text Add to dashboard Cite

“…Treatment of compounds (1) overnight in liquid ammonia gave essentially quantitative yields of the hydroxypyrrolines (6), which on heating in acetic acid, or to their melting points without solvent, were converted in very high yields into the pyrroles (3). Compounds (6) thus appear to be intermediates in the reaction shown in Scheme 2.…”

mentioning

confidence: 99%

“…Compounds (6) thus appear to be intermediates in the reaction shown in Scheme 2. Their conversion into the 1H-pyrroles (3) may be either by dehydration to the 3Hpyrroles (2) followed by two successive acyl [ 1,5]-shifts [disfavoured by the observed transformation (4) --.) ( 5 ) which would require a highly strained intermediate by this route], or as shown in Scheme 3.…”

mentioning

confidence: 99%