2199-54-4Relevant academic research and scientific papers
Ring-contraction of hantzsch esters and their derivatives to pyrrolesviaelectrochemical extrusion of ethyl acetate out of aromatic rings
Liu, Xu,Liu, Chang,Cheng, Xu
, p. 3468 - 3473 (2021/05/21)
Electrochemical ring-contraction of HEs and theirs pyridine derivatives is developed to obtain polysubstituted pyrroles. This process provides an orthogonal utilization of Hantzsch esters for the well-documented application as side chain or hydrogen donors. The formal transformation shows an extrusion of ethyl acetate out of the pyridine ring in a single step. In addition to the novel transformation, we also discovered the Lewis acid's intermolecular control of regioselectivity during an intramolecular electrochemical process. The reaction provides a number of polysubstituted pyrroles that have never been accessed, including pharmaceutical intermediates and photoswitches. An unusual 4-electron continuous reduction drives the unprecedented anionic dearomatization/ring-contraction/rearomatization pathway.
Tuning azoheteroarene photoswitch performance through heteroaryl design
Calbo, Joaquín,Weston, Claire E.,White, Andrew J. P.,Rzepa, Henry S.,Contreras-García, Julia,Fuchter, Matthew J.
supporting information, p. 1261 - 1274 (2017/05/15)
Photoswitchable compounds, which can be reversibly switched between two isomers by light, continue to attract significant attention for a wide array of applications. Azoheteroarenes represent a relatively new but understudied type of photoswitch, where one of the aryl rings from the conventional azobenzene class has been replaced with a fivemembered heteroaromatic ring. Initial studies have suggested the azoheteroarenes-the arylazopyrazoles in particular- to have excellent photoswitching properties (quantitative switching and long Z isomer half-life). Here we present a systematic computational and experimental study to elucidate the origin of the long thermal half-lives and excellent addressability of the arylazopyrazoles, and apply this understanding to determine important structure-property relationships for a wide array of comparable azoheteroaryl photoswitches. We identify compounds with Z isomer half-lives ranging from seconds to hours, to days and to years, and variable absorption characteristics, all through tuning of the heteraromatic ring. Conformation perhaps plays the largest role in determining such properties: the compounds with the longest isomerization half-lives adopt a T-shaped ground state Z isomer conformation and proceed through a T-shaped isomerization pathway, whereas the most complete photoswitching is achieved for compounds that have a twisted (rather than T-shaped) Z isomer conformation. By balancing these factors, we report a new azopyrazole 3pzH, which can be quantitatively switched to its Z isomer (1/2 = 74 d at 25 °C). Given the large tunability of their properties, the predictive nature of their performance, and the other functional opportunities afforded by usage of a heteroaromatic system, we believe the azoheteroaryl photoswitches to have huge potential in a wide range of optically addressable applications.
Versatility of Weinreb amides in the Knorr pyrrole synthesis
Alberola, Angel,Ortega, Alfonso Gonzalez,Sadaba, M. Luisa,Sanudo, Carmen
, p. 6555 - 6566 (2007/10/03)
N-Methoxy-N-methyl-α-enaminocarboxamides were prepared starting from enamines and Weinreb α-aminoamides. Their reaction with oganometallic compounds and subsequent cyclization constitute a versatile alternative in the Knorr pyrrole synthesis.
Synthesis and physicochemical properties of hydrobromides of alkyl-substituted dipyrrolylmethenes
Berezin,Semeikin,Antina,Pashanova,Lehedeva,Bukushina
, p. 1949 - 1955 (2007/10/03)
Hydrobromides of [(alkylpyrrol-2(1H)-ylidenio)methyl]pyrroles (α,α-dipyrrolylmethenes) and of their α,β and β,β isomers were prepared, and their resistance to oxidative thermal degradation was studied. The solvation properties of these compounds in various organic solvents were examined spectrophotometrically and calorimetrically.
THE SYNTHESIS AND CHEMISTRY OF AZOLENINES. PART 18. PREPARATION OF 3-ETHOXYCARBONYL-3H-PYRROLES VIA THE PAAL-KNORR REACTION, AND SIGMATROPIC REARRANGEMENTS INVOLVING COMPETITIVE ESTER MIGRATIONS TO C-2, C-4 AND N.
Chiu, Pak-Han,Sammes, Michael P.
, p. 3439 - 3456 (2007/10/02)
3H-Pyrrole-3-carboxylic esters (4) have been prepared, in some cases together with isomers (5) and (6) having exocyclic double bonds, by cyclization of suitably substituted 2-ethoxycarbonyl-1,4-diketones (1) with liquid ammonia, followed by dehydration of the isolable 2-hydroxy-3,4-dihydro-2H-pyrrole intermediates (2) and (3) with aluminia in boiling solvents.Prolonged heating in toluene or p-xylene converts the 3H-pyrroles (4) quantitatively into isomeric 4-esters (11) and N-esters (13) of 1H-pyrroles via competitive sigmatropic rearrangements.Isolable intermediate 2H-pyrrole-2-carboxylic esters (12) are converted similarly into the same products, under the same conditions.Detection of 3H-pyrroles (4) as intermediates in the latter reaction demonstrates for the first time the reversibility of the thermal 2H-pyrrole to 3H-pyrrole interconversion.
THERMAL REARRANGEMENT OF 3H-PYRROLES BY COMPETITIVE -SIGMATROPIC SHIFTS, AND THE REVERSIBILITY OF THE 3H- TO 2H-PYRROLE INTERCONVERSION
Chiu, Pak-Kan,Sammes, Michael P.
, p. 2775 - 2778 (2007/10/02)
3-Ethoxycarbonyl-3H-pyrroles are converted via thermal -ester shifts to the isomeric 1H-pyrrole-4- and N-esters.Isolable intermediate 2H-pyrroles are converted into the same products, and also into the 3H-pyroles, demonstrating conclusively the reversibility of the 3H- to 2H-pyrrole interconversion.
The Chemistry of Pyrrolic Compounds.LVIII meso-Substituted Porphyrins : Further Observations on the Oxidative Cyclization of Bilenes-b
Clezy, Peter S.,Duncan, Mark W.,Ravi, B.N.,Thuc, Le van
, p. 399 - 418 (2007/10/02)
The oxidative cyclization of series of bilenes-b carrying substituted methyl groups at a terminal site (1d-i) hes been investigated as an approach to the synthesis of meso-substituted porphyrins.Although in most cases the required porphyrin was formed the
Alkylation process
-
, (2008/06/13)
Substituted pyrrole compounds, such as 3-ethyl-4-methyl-5-carbethoxy pyrrole, 2,4-dimethyl-3-acetyl pyrrole and 2-methyl-5-carboxy pyrrole-4-propionic acid diethyl ester, are alkylated in a single step by reaction with an aldehyde or ketone in the presence of both an acid condensing agent such as hydriodic acid and a compatible reducing agent such as metallic zinc or stannous chloride. Suitable carbonyl reactants include formaldehyde, paraldehyde, isobutyraldehyde, acetone, cyclohexanone and methyl-isobutyl ketone. This application is a continuation application of U.S. application Ser. No. 281,624 filed Aug. 18, 1972, now abandoned, which is a continuation-in-part application of U.S. application Ser. No. 832,001, filed June 10, 1969, now abandoned.
