<i>N</i>,<i>N</i>′-Bipyrroyl

Flitsch, Wilhelm; Schulten, W.

doi:10.1055/s-1977-24421

Cited by 12 publications

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“…The cold finger was cooled to −30 °C, and the sublimator was connected to a high vacuum pump and the bipyrrole crystals were collected shortly on the cold finger. The cold finger was removed carefully, and the solid was scraped off and collected to give 295 mg (37% yield) of product 1 [mp 52 °C (sealed tube)] (lit . mp 57 °C).…”

Section: Methodsmentioning

confidence: 99%

“…15 Given the differences between the predicted conformation of 2,2′-bipyrrole and that found in its crystal, and the general prediction that bipyrroles are twisted, we were attracted to determine the crystal structure conformation of 1,1′-bipyrrole, which is a solid with a reported mp 57°C. 9 1,1′-Bipyrroles were apparently first synthesized in 1904, 16 the first bipyrroles (2,2′,5,5′-dimethyl-1,1′-bipyrrole-3,3′-dicarboxylic acid) to have been synthesized, by condensing 1,4-dione (ethyl 3-acetyl-5-oxohexanoate) with hydrazine in a reaction that proceeded stepwise through 1-aminopyrrole. Our syntheses of the parent 1,1′-bipyrrole (1) follows a similar path, as outlined in Scheme 1.…”

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“…All but one, 1,1‘-bipyrrole, have C−C or N−C bonds linking the two pyrrole rings. Four of the six parent, unsubstituted bipyrroles (1,1‘, 2,2‘, 3,3‘, and 2,3‘) have been synthesized in 1976 and 1977, and subsequent spectroscopic and theoretical analyses , were reported in only a few publications. Unlike biphenyls and other biaryls, rotational stereochemistry (atropisomerism) about the interconnecting bond of the six possible bipyrrole isomers is not well understood. , …”

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confidence: 99%

“…And although crystallographic structures of octa-substituted 1,1‘-bipyrroles may not reflect that of the parent, octamethyl- and octa(trifluoromethylthio)-1,1‘-bipyrrole were found to have orthogonal rings (92.4 and 92.8°, respectively) . Given the differences between the predicted conformation of 2,2‘-bipyrrole and that found in its crystal, and the general prediction that bipyrroles are twisted, we were attracted to determine the crystal structure conformation of 1,1‘-bipyrrole, which is a solid with a reported mp 57 °C …”

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1,1‘-Bipyrroles: Synthesis and Stereochemistry

Dey

Lightner

2007

J. Org. Chem.

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Abstract1,1′-Bipyrrole is synthesized in four steps from hydrazine. A colorless solid, mp 52°C, it sublimes readily at room temperature and forms X-ray quality crystals in which the rings are not coplanar but are nearly orthogonal.Bipyrroles 1 are N-heterocyclic analogs of biphenyl, although far less well studied. Bipyrrole articles entered the literature only about a dozen times during the first half of the last century; yet, in the past 25 years there has been a relative explosion of interest in bipyrroles and bipyrrole-based more complex structures with more than 400 citations. Bipyrroles are found in nature as components of clinically interesting and important natural products for the treatment of cancer, viral and bacterial infection 2 ; (in reduced form) in vitamin-B 12 3 ; in marine natural products 4 ; in macrocyclic oligopyrroles for use as ionophores 5 and in medicine 6 ; and in synthetic linear oligopyrrole conductive polymers. 7There are six different bond connections that can be drawn between two pyrrole molecules, leading to six constitutionally isomeric bipyrroles: 3 symmetric (1,1′; 2,2′; and 3,3′) and 3 nonsymmetric (1,2′; 1,3′; and 2,3′). All but one, 1,1′-bipyrrole, have C-C or N-C bonds linking the two pyrrole rings. Four of the six parent, unsubstituted bipyrroles (1,1′, 2,2′, 3,3′, and 2,3′) have been synthesized in 1976 8 and 1977, 9 and subsequent spectroscopic 10 and theoretical analyses 11,12 were reported in only a few publications. Unlike biphenyls and other biaryls, rotational stereochemistry (atropisomerism) about the interconnecting bond of the six possible bipyrrole isomers is not well understood. 1,12In contrast to the well-studied atropisomeric stereochemistry of biaryls, 13 there are only two known optically active bipyrroles: a 1,1′-bipyrrole (2,2′,5,5′-tetramethyl-1,1′-bipyrrole-3,3′-dicarboxylic acid) 14a and a 2,2′-bipyrrole (1,1′,2,2′,5,5′-hexamethyl-2,2′-bipyrrole-3,3′-dicarboxylic acid). 14b Molecular orbital calculations and photoelectron spectroscopy have indicated a preference for orthogonal rings in 1,1′-bipyrrole. 10 Ab initio calculations on 2,2′-bipyrrole show it adopting preferentially an anti-clinal (ac) conformation at the global minimum with an N-2-2′-N' torsion angle ∼148° and a 3-4 kcal/mole greater stability than the sc local minimum conformation, where the N-2-2′-N' torsion angle is ∼46°. 11,12b Theory also predicts the ac conformations of 3,3′-and 2,3′-bipyrrole to be the most stable. 11a,c NIH Public Access Such theoretical predictions do not necessarily relate to the solid phase: an X-ray structure of 2,2′-bipyrrole shows it to adopt an ap planar conformation in the crystal. 12 There are no crystal structures available of any of the other parent constitutional isomers of bipyrrole. And although crystallographic structures of octa-substituted 1,1′-bipyrroles may not reflect that of the parent, octamethyl-and octa(trifluoromethylthio)-1,1′-bipyrrole were found to have orthogonal rings (92.4° and 92.8°, respectively). 15 Given the differences between the p...

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Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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1,1‘-Bipyrroles: Synthesis and Stereochemistry

Dey

Lightner

2007

J. Org. Chem.

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TheVilsmeier Reaction of Fully Conjugated Carbocycles and Heterocycles

Jones

Stanforth

1996

Organic Reactions

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In 1925 Fischer, Müller, and Vilsmeier published a paper describing the reaction between phosphoryl chloride and N ‐methylacetanilide, giving a number of products, including the quinolinium salt and another salt. The probable course of the reaction was given in a paper by Vilsmeier and Haack in 1927, and they made the important discovery that the reagent obtained from N ‐methylformanilide and phosphoryl chloride, represented as a salt, would react with N,N ‐dimethylaniline, giving 4‐ N,N ‐dimethylaminobenzaldehyde. No 2‐substituted products were observed in this reaction. Other N,N ‐dialkylaniline derivatives, including 3, N,N ‐trimethylaniline and 1‐ N,N ‐dimethylaminonaphthalene were also successfully used as substrates to prepare aromatic aldehyde derivatives. The gradual development of the reagent for synthesis was accompanied by interest in the nature of the reagent. It was discovered that other acid chlorides (e.g., thionyl chloride, carbonyl chloride, and oxalyl chloride) could be used in the reaction and that substituted amides other than formamides gave ketones, although in generally poorer yields. Thionyl chloride frequently gives sulfur‐containing products. The most commonly used amide is dimethylformamide (DMF) and there is now a consensus that the reagent formed from DMF and most acid chlorides, other than phosphoryl chloride, can be represented by the structure given in the chapter, and this is illustrated for the reaction between DMF and carbonyl chloride. The salt is a stable compound and is often isolated before being reacted with a substrate. It seems likely that the most commonly used reagent, that made from DMF and phosphoryl chloride, is an equilibrium mixture of iminium salts. Recent unpublished spectroscopic studies have indicated that in DMF solution there is an equilibrium mixture of iminium compounds. One of the electrophilic chloroiminium salts then reacts with a substrate in an electrophilic substitution process yielding an iminium salt, which is usually hydrolyzed to the aromatic aldehyde. Vinylogous chloroiminium salts can be prepared from the corresponding vinylogous formamide derivatives and these yield, after hydrolysis, α,β‐unsaturated products. This particular reaction is generally limited to more reactive substrates. The formation of carbon–carbon bonds to fully conjugated carbocycles and heterocycles is the subject of this chapter; a subsequent chapter considers carbon–carbon bond‐formation reactions in alkenes (including heterosubstituted alkenes such as enamines and enol ethers), alkynes, and activated methyl and methylene compounds (aldehydes, ketones, carboxylic acid derivatives, and nitriles). It is not surprising that the Vilsmeier reaction has been the subject of many review articles of varying scope and length. With so many excellent reviews dealing with the Vilsmeier reaction, its mechanism, and the structure of the various electrophilic reagents, coverage is restricted to important concepts rather than reiterate all the literature material. A brief description of the mechanism and regiochemistry of the Vilsmeier reaction is presented and this is elaborated with appropriate cases that deal with specific compound types.

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The Synthesis of 1H‐Pyrroles

Bean

1990

Chemistry of Heterocyclic Compounds: A Series of Monographs

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N,N′-Bipyrroyl

Cited by 12 publications

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1,1‘-Bipyrroles: Synthesis and Stereochemistry

1,1‘-Bipyrroles: Synthesis and Stereochemistry

TheVilsmeier Reaction of Fully Conjugated Carbocycles and Heterocycles

The Synthesis of 1H‐Pyrroles

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