Categories: Synthesis of N-Heterocycles >
Synthesis of pyrroles
An operationally simple, practical, and economical Paal-Knorr pyrrole condensation of 2,5-dimethoxytetrahydrofuran with various amines and sulfonamines in water in the presence of a catalytic amount of iron(III) chloride allows the synthesis of N-substituted pyrroles under very mild reaction conditions in good to excellent yields.
N. Azizi, A. Khajeh-Amiri, H. Ghafuri, M. Bolourtchian, M. R. Saidi, Synlett, 2009, 2245-2248.
A general, selective, and atom economic metal-catalyzed conversion of primary diols and amines to highly valuable 2,5-unsubstituted pyrroles is catalyzed by a stable manganese complex in the absence of organic solvents. Water and molecular hydrogen are the only side products. The reaction shows unprecedented selectivity, avoiding the formation of pyrrolidines, cyclic imides, and lactones.
J. C. Borghs, Y. Lebedev, M. Rueping, O. El-Sepelgy, Org. Lett., 2019, 21, 70-74.
A Cu/ABNO-catalyzed aerobic oxidative coupling of diols and a broad range of primary amines provides N-substituted pyrroles. The reaction proceeds at room temperature with an O2 balloon as the oxidant using commercially available materials as the substrates and catalysts. The catalyst system offers a good tolerance to sensitive functional groups.
W. Fu, L. Zhu, S. Tan, Z. Zhao, X. Yu, L. Wang, J. Org. Chem., 2022, 87, 13389-13395.
In ionic liquids [Bmim][PF6] or [Bmim][BF4], a highly regioselective N-substitution of pyrrole with alkyl halides, sulfonyl chlorides, and benzoyl chloride gave substituted pyrroles in excellent yields. Michael addition of pyrrole with electrophilic olefins was completed in a highly regioselective manner to afford N-alkylpyrroles.
Z.-G. Lea, Z.-C. Chen, Y. Hu, Q.-G. Zheng Synthesis, 2004, 1951-1954.
A method for the preparation of N-acylpyrroles involves condensation of carboxylic acids with 2,4,4-trimethoxybutan-1-amine, followed by acid-mediated cyclization to form the pyrrole ring. The preparative procedure is highly tolerant of various functional groups.
T. Maehara, R. Kanno, S. Yokoshima, T. Fukuyama, Org. Lett., 2012, 14, 1946-1948.
N-Sulfonyl- and N-acylpyrroles were synthesized via olefin ring-closing metathesis of diallylamines followed by in situ oxidative aromatization in the presence of the ruthenium Grubbs catalyst and a suitable copper catalyst. Under an oxygen atmosphere, the reaction worked smoothly without the need of hydroperoxide oxidants.
W. Chen, Y.-L. Zhang, H.-J. Li, X. Nan, Y. Liu, Y.-C. Wu, Synthesis, 2019, 51, 3651-3666.
A general and efficient Cu-assisted cycloisomerization of alkynyl imines enables an efficient synthesis of pyrroles and various types of fused heteroaromatic compounds.
A. V. Kel'in, A. W. Sromek, V. Gevorgyan, J. Am. Chem. Soc., 2001, 123, 2074-2075.
The use of ruthenium-based pincer-type catalysts enables the synthesis of substituted pyrroles via dehydrogenative alcohol functionalization reactions. Various substituted pyrroles were prepared via dehydrogenative coupling of secondary alcohols and amino alcohols.
A. K. Guin, R. Mondal, G. Chakraborty, S. Pal, N. D. Paul, J. Org. Chem., 2022, 87, 7106-7123.
Pd, Ru, and Fe catalysis enable a general synthesis of 2-substituted pyrroles in overall good yields with only water and ethene as side-products. The route starts with two subsequent Pd-catalyzed monoallylations of amines with allylic alcohols. Ru-catalyzed ring-closing metathesis performed on the diallylated amines provides pyrrolines in excellent yields. By addition of ferric chloride, a selective aromatization was achieved.
A. Bunrit, S. Sawadjoon, S. Tšupova, P. J. R. Sjöberg, J. S. M. Samec, J. Org. Chem., 2016, 81, 1450-1460.
In the reaction of 1,3-dienylboronic esters with nitrosoarenes, a one-pot hetero-Diels-Alder/ring contraction cascade affords N-arylpyrroles with low to good yields depending on the electronic properties of the substituents on the borodiene, whereas an sp3 boron substituent led to the formation of stable boro-oxazines with high regioselectivity.
L. Eberlin, B. Carboni, A. Whiting, J. Org. Chem., 2015, 80, 6574-6583.
Gold-catalyzed cyclizations of diols and triols to the corresponding hetero- or spirocycles take place in an aqueous medium within nanomicelles, where the hydrophobic effect is operating, thereby driving the dehydrations, notwithstanding the surrounding water. By the addition of simple salts such as sodium chloride, reaction times and catalyst loadings can be significantly decreased.
S. R. K. Minkler, N. A. Isley, D. J. Lippincott, N. Krause, B. H. Lipshutz, Org. Lett., 2014, 16, 724-726.
A synthesis of substituted pyrroles by a gold(I)-catalyzed cascade reaction proceeds via an autotandem catalysis consisting of an initial addition of gold-acetylide to an acetal moiety followed by gold-catalyzed 5-endo-dig cyclization and aromatization. This formal (3 + 2) annulation of two components provides various substituted pyrroles in a modular fashion.
H. Ueda, M. Yamaguchi, H. Kameya, K. Sugimoto, H. Tokuyama, Org. Lett., 2014, 16, 4948-4951.
A transition metal-free one-pot reaction of secondary alcohols and 2-aminoalcohols provides various substituted NH-pyrroles via an Oppenauer oxidation in the presence of benzophenone as an inexpensive reagent. The oxidation of the secondary alcohols under mild condition to ketones is followed by an in situ condensation with aminoalcohol, and oxidative cyclization to the target pyrrole ring.
J.-A. Shin, J. Kim, H. Lee, S. Ha, H.-Y. Lee, J. Org. Chem., 2019, 84, 4558-4565.
A Pd(II)-catalyzed oxidative approach to construct polysubstituted pyrroles from N-homoallylicamines and arylboronic acids proceeds through cascade formation of C-C and C-N bonds via oxidative arylation of unactive alkenes, followed by intramolecular aza-Wacker cyclization.
J. Zheng, L. Huang, C. Huang, W. Wu, H. Jiang, J. Org. Chem., 2015, 80, 1235-1242.
A nano copper-catalyzed reaction of vinyl azides with terminal alkynes provides 2,5-disubstituted pyrroles in high yield with aryl alkynes and aliphatic alkynes, whereas 2,3,4-trisubstituted pyrroles were formed with silylated alkynes. The reactions offer high efficiency, excellent regioselectivity, and good functional group compatibility.
J. Cen, Y. Wu, J. Li, L. Huang, W. Wu, Z. Zhu, S. Yang, H. Jiang, Org. Lett., 2019, 21, 2090-2094.
Nitrogen-containing heterocycles, including 1H-indoles and electron-deficient 1H-pyrroles, undergo a smoth and mild palladium/norbornene-cocatalyzed regioselective alkylation with primary alkyl bromides at the C-H bond adjacent to the NH group to give 2-alkyl-1H-indoles and 2-substituted or 2,3-disubstituted 5-alkyl-1H-pyrroles in good yields.
L. Jiao, T. Bach, Synthesis, 2014, 46, 35-41.
Rhodium-catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with vinyl ethers enables the synthesis of mono-, di-, and trisubstituted pyrroles. Furthermore, the developed methodology was applied in the formal synthesis of neolamellarin A, an antitumor agent.
S. Rajasekar, P. Anbarasan, J. Org. Chem., 2014, 79, 8438-8434.
Gold(I) catalysis enables an efficient synthesis of N-protected pyrroles and 5,6-dihydropyridin-3(4H)-ones from N-protected and unprotected 5-aminopent-2-yn-1-ol, respectively. Atom-economic syntheses of hydroxyalkyl indoles and benzofurans are also described. The methods offer short reaction time, low catalyst loading, high yield, and simple open-flask reaction conditions.
N. Bera, B. S. Lenka, S. Bishi, S. Samanta, B. Sarkar, J. Org. Chem., 2022, 87, 9729-9754.
The reaction of 4-nitro-1,3-diarylbutan-1-ones and ammonium acetate in the presence of morpholine and sulfur provides the corresponding 2,4-diarylpyrroles in excellent yields.
M. Adib, N. Ayashi, F. Heidari, P. Mirzaei, Synlett, 2016, 27, 1738-1742.
An efficient copper hydride (CuH)-catalyzed enyne-nitrile coupling reaction provides polysubstituted N-H pyrroles bearing a broad range of functional groups in good yields with high regioselectivity. The Cu-based catalyst promotes both the initial reductive coupling and subsequent cyclization steps.
Y. Zhou, L. Zhou, L. T. Jesikiewicz, P. Liu, S. L. Buchwald, J. Am. Chem. Soc., 2020, 142, 9908-9914.
A Pd-catalyzed decarboxylative reaction of readily available cyclic carbonates and amines provides highly functionalized pyrroles and only generates CO2 and H2O as byproducts. The reaction works at room temperature and open to air, and is suitable for the derivatization of bioactive compounds.
L. Zuo, Y. Yang, W. Guo, Org. Lett., 2021, 23, 2013-2018.
A gold-catalyzed cascade hydroamination/cyclization reaction of α-amino ketones with alkynes gives substituted pyrroles. The method offers high regioselectivity, wide functional group tolerance, and easily accessible starting materials.
X. Li, M. Chen, X. Xie, N. Sun, S. Li, Y. Liu, Org. Lett., 2015, 17, 2984-2987.
An efficient and base-mediated intramolecular cyclization of N-propargylamines provides structurally diversified pyrroles in high yield. The method is broadly applicable and tolerates various functional groups.
P. K. Mishra, S. Verma, M. Kumar, A. K. Verma, Org. Lett., 2018, 20, 7182-7185.
A silver-catalyzed formal [3 + 2] cycloaddition reaction, with cyclopropanols as a C3 subunit and imines as a two-atom subunit, takes place under mild conditions and produces a broad array of polysubstituted pyrroles in good yields.
Y. Zhou, M. Wu, Y. Liu, C. Cheng, G. Zhu, Org. Lett., 2020, 22, 7542-7546.
An I2-mediated reaction of pyridinium salts provides diversely substituted 2-formylpyrroles in good yields under operationally simple conditions. The reaction proceeds via a H2O-triggered ring opening of the pyridinium salt and a subsequent intramolecularly nucleophilic addition sequence.
K. Xu, W. Li, R. Sun, L. Luo, X. Chen, C. Zhang, X. Zheng, M. Yuan, H. Fu, R. Li, H. Chen, Org. Lett., 2020, 22, 6107-6111.
Acid chlorides can be activated to transient acid iodide intermediates using a simple iodide source. This indermediates undergo nucleophilic attack from a variety of relatively weak nucleophiles - including Friedel-Crafts acylation of N-methylpyrroles, N-acylation of sulfonamides, and acylation reactions of hindered phenol derivatives.
R. J. Wakeham, J. E. Taylor, S. D. Bull, J. A. Morris, J. M. J. Williams, Org. Lett., 2013, 15, 702-705.
A regioselective Minisci monoacylation of electron-rich pyrroles under silver-free neutral conditions provides the desired products without polymerization of pyrroles.
J. K. Laha, M. K. Hunjan, S. Hegde, A. Gupta, Org. Lett., 2020, 22, 1442-1447.
A mechanochemical van Leusen pyrrole synthesis provides 3,4-disubstitued pyrroles in good yields. The developed protocol is compatible with a range of electron-withdrawing groups and was also applied to a van Leusen oxazole synthesis.
C. Schumacher, C. Molitor, S. Smid, K.-N. Truong, K. Rissanen, C. Bolm, J. Org. Chem., 2021, 86, 14213-14222.
In ruthenium-catalyzed three-component reactions, ketones, amines, and vicinal diols are converted into various substituted pyrroles in good isolated yields. Additionally, α-functionalized ketones gave synthetically interesting amido-, alkoxy-, aryloxy-, and phosphate-substituted pyrroles in a straightforward manner. The synthetic protocol proceeds with high atom-efficiency and shows a broad substrate scope and functional group tolerance.
M. Zahng, X. Fang, H. Neumann, M. Beller, J. Am. Chem. Soc., 2013, 135, 11384-11388.
The dual effects of a catalytic ruthenium complex and an alkali metal base enable a virtually salt-free and straightforward bimolecular assembly giving N-unsubstituted pyrroles through fully unmasked α-amino aldehydes. Either solvent-free or acceptorless dehydrogenation achieve high atom step and pot economy by avoiding multistep operations involving protection/deprotection.
K. Iida, T. Miura, J. Ando, S. Saito, Org. Lett., 2013, 15, 1436-1439.
An efficient Au(I)-catalyzed propargyl-claisen rearrangement and 5-exo-dig cyclization of tertiary enamides provided a variety of pentasubstituted pyrroles derivatives with excellent functional group tolerance in excellent yields.
W. Li, R. Shi, S. Chen, X. Zhang, W. Peng, S. Chen, J. Li, X.-M. Xu, Y.-P. Zhu, X. Wang, J. Org. Chem., 2022, 87, 3014-3024.
An iodoxybenzoic acid-mediated selected oxidative cyclization of N-hydroxyalkyl enamines provides a variety of 2,3-disubstituted pyrroles and pyridines in good selectivity. This metal-free method offers use of environmentally friendly reagents, broad substrate scope, mild reaction conditions, and high efficiency.
P. Gao, H.-J. Chen, Z.-J. Bai, M.-N. Zhao, D. Yang, J. Wang, N. Wang, L. Du, Z.-H. Guan, J. Org. Chem., 2020, 85, 7939-7951.
When treated with zinc chloride in refluxing chloroform, N-propargylic β-enaminones produced in situ 2-methylene-2,3-dihydro-1,4-oxazepines, which, upon further refluxing in methanol with zinc chloride, afforded 2-acetyl-1H-pyrroles in good yields. This one-pot two-step protocol was found to be general for a wide variety of substrates with good functional group tolerance.
N. Kanova, B. A. Dundar, Y. Kelgokmen, M. Zora, J. Org. Chem., 2021, 86, 6289-6304.
1-Sulfonyl-1,2,3-triazoles alkynes gave α-imino rhodium carbene complexes, which afforded substituted pyrroles when reacted with alkenyl alkyl ethers. The method can be efficiently applied to a one-pot sequential reaction starting from terminal alkynes.
C.-E. Kim, S. Park, D. Eom, B. Seo, P. H. Lee, Org. Lett., 2014, 16, 1900-1903.
Enyne cross metathesis of propargylamines with ethyl vinyl ether provides a series of substituted pyrroles, bearing alkyl, aryl, and heteroaryl substituents under microwave irradiation.
H. Chachignon, N. Scalacci, E. Petricci, D. Castagnolo J. Org. Chem., 2015, 80, 5287-5295.
A highly efficient Cu-catalyzed tandem C-N bond-forming reaction of 1,4-dihalo-1,3-dienes allows the synthesis of pyrroles and heteroarylpyrroles with a wide variety of functional groups and substitution patterns from readily available precursors.
R. Martín, C. H. Larsen, A. Cuenca, S. L. Buchwald, Org. Lett., 2007, 9, 3379-3382.
An efficient copper-catalyzed double alkenylation of amides with (1Z,3Z)-1,4-diiodo-1,3-dienes affords di- or trisubstituted N-acylpyrroles in good yields using CuI as the catalyst, Cs2CO3 as the base, and rac-trans-N,N'-dimethylcyclohexane-1,2-diamine as the ligand.
X. Yuan, X. Xu, X. Zhou, J. Yuan, L. Mai, Y. Li, J. Org. Chem., 2007, 72, 1510-1513.
A tandem reaction involving cross metathesis followed by concomitant cyclisation enables the synthesis of substituted pyrroles. Various protected electron-deficient N-allylamines reacted with α,β-unsaturated carbonyl compounds in the presence of Lewis acids under the cross metathesis conditions using a 2nd generation Hoveyda catalyst in order to form pyrroles.
S. Shafi, M. Kędziorek, K. Grela, Synlett, 2011, 124-128.
Titanium-catalyzed intermolecular hydroaminations enabled efficient, user-friendly one-pot reactions for the preparations of 2-substituted and fully substituted pyrroles from (E/Z)-chloroenynes and easily accessible α-haloalkynols, respectively.
L. Ackermann, R. Sandmann, L. T. Kaspar, Org. Lett., 2009, 11, 2031-2034.
Nucleophilic addition of sulfonamides to 1-bromo-1-alkynes provided (Z)-N-(1-bromo-1-alken-2-yl)-p-toluenesulfonamides in good yield and in a highly regio- and stereoselective manner. A subsequent reaction in the presence of a palladium catalyst under Heck conditions afforded substituted pyrroles in good yield.
M. Yamagishi, K. Nishigai, T. Hata, H. Urabe, Org. Lett., 2011, 13, 4873-4875.
A facile and efficient protocol enabled the synthesis of 1,2,4-substituted pyrrole derivatives from ready available starting materials. This type of reaction should have potential utility in organic synthesis.
D. Zhu, J. Zhao, Y. Wei, H. Zhou, Synlett, 2011, 2185-2186.
Intramolecular cyclizations of 3-alkyne-1,2-diols and 1-amino-3-alkyn-2-ols with very low catalyst loading of (Ph3P)AuCl-AgNTf2 or (Ph3P)AuCl-AgOTf proceeded at room temperature to provide various substituted furans and pyrroles in excellent yields. This method was also fully applicable to the conversion of 26 g of a substrate using only 0.05 mol % each of the Au and Ag catalysts.
M. Egi, K. Azechi, S. Akai, Org. Lett., 2009, 11, 5002-5005.
Copper or nickel catalyzed highly selective denitrogenative annulations of vinyl azides with aryl acetaldehydes afford 2,4- and 3,4-diaryl substituted pyrroles depending on the selection of the transition metal catalyst. Compared with the reported acidic or basic conditions for polysubstituted pyrrole synthesis, the reaction conditions are mild, neutral, and very simple without any additives.
F. Chen, T. Shen, Y. Cui, N. Jiao, Org. Lett., 2012, 14, 4926-4929.
A cyclization of α-amino carbonyl compounds and aldehydes catalyzed by I2 enables a synthesis of 1,3,4-triarylpyrroles. This reaction proceeds smoothly in good yields and tolerates various functional groups.
R. Yan, X. Kang, X. Zhou, X. Li, X. Liu, L. Xiang, Y. Li, G. Huang, J. Org. Chem., 2014, 79, 465-470.
An efficient Fe-catalyzed radical cycloaddition of enamides and 2H-azirines enables the synthesis of substituted pyrroles. The reaction works with readily available starting materials, tolerates various functional groups, and affords valuable triaryl-substituted pyrroles in very good yields under mild reaction conditions.
M.-N. Zhao, Z.-H. Ren, D.-S. Yang, Z.-H. Guan, Org. Lett., 2018, 20, 1287-1290.
Manganese(III)-catalyzed formal [3+2] annnulation of vinyl azides and β-keto acids enables the synthesis of substituted NH pyrroles with a wide range of substituents.
E. P. J. Ng, Y.-F. Wang, S. Chiba, Synlett, 2011, 783-786.
1-Sulfonyl-1,2,3-triazoles, readily prepared by copper-catalyzed azide-alkyne cycloaddition, react with allenes in the presence of a nickel(0) catalyst to produce isopyrroles. These intermediates are further converted to a wide range of polysubstituted pyrroles through double bond transposition and Alder-ene reactions.
T. Miura, K. Hiraga, T. Biyajima, T. Nakamuro, M. Murakami, Org. Lett., 2013, 15, 3298-3301.
Furans, pyrroles, and thiophenes are efficiently and conveniently prepared by gold-catalyzed dehydrative cyclizations of readily available, heteroatom-substituted propargylic alcohols. The reactions provide essentially pure aromatic heterocycles in high yields in minutes under open-flask conditions with low catalyst loadings.
A. Aponick, C.-Y. Li, J. Malinge, E. F. Marques, Org. Lett., 2009, 11, 4624-4627.
A convenient and general one-pot synthesis of substituted pyrroles from propargylic acetates, silyl enol ethers, and primary amines was catalyzed by indium trichloride. High yields of various pyrrole derivatives were obtained.
M. Lin, L. Hao, R.-d. Ma, Z.-p. Zhan, Synlett, 2010, 2345-2351.
Highly substituted furans were conveniently synthesized by the platinum-catalyzed reaction of propargylic oxiranes. Propargylic aziridines were also reacted with the platinum catalyst to produce the corresponding substituted pyrroles in good yields.
M. Yoshida, M. Al-Amin, K. Shishido, Synthesis, 2009, 2454-2466.
Aryl-substituted N-tosyl alkynyl aziridines undergo a gold-catalyzed ring expansion to afford 2,5-substituted pyrrole products. Depending on the the counterion to the gold catalyst and the solvent, a ring-expansion and rearrangement leads to 2,4-substituted pyrroles.
P. W. Davies, N. Martin, Org. Lett., 2009, 11, 2293-2296.
Titanium-catalyzed intermolecular hydroaminations enabled efficient, user-friendly one-pot reactions for the preparations of 2-substituted and fully substituted pyrroles from (E/Z)-chloroenynes and easily accessible α-haloalkynols, respectively.
L. Ackermann, R. Sandmann, L. T. Kaspar, Org. Lett., 2009, 11, 2031-2034.
Copper catalysis enables the synthesis of polysubstituted pyrroles from aldehydes, amines, and β-nitroalkenes. Remarkably, the use of α-methyl-substituted aldehydes provides efficient access to a series of tetra- and pentasubstituted pyrroles via an overwhelming 1,2-phenyl/alkyl migration. Non α-substituted aldehydes provide the corresponding trisubstituted pyrroles.
D. Andreou, M. G. Kallitsakis, E. Loukopoulos, C. Gabries, G. E. Kostakis, J. N. Lykakis, J. Org. Chem., 2018, 83, 2104-2113.
(Hetero)aryl-, alkenyl-, and selected alkyl-substituted acid chlorides can be efficiently coupled with N-Boc-protected propargylamine to produce ynones which are converted to 2-substituted N-Boc-4-iodopyrroles in a one-pot reaction. Upon addition of a further alkyne, another Sonogashira coupling can be carried out in a one-pot fashion.
E. Merkul, C. Boersch, W. Frank, T. J. J. Müller, Org. Lett., 2009, 11, 2269-2272.
Low-valent rhodium complexes efficiently catalyze an activation of α-C-H bond of isonitriles. An addition of isonitriles to carbonyl compounds proceeds under mild and neutral conditions to give the corresponding α,β-unsaturated formamides. An in situ cyclocondensation with 1,3-dicarbonyl compounds provides pyrroles.
H. Takaya, S. Kojima, S.-I. Murahashi, Org. Lett., 2001, 3, 421-424.
Cyclization, aromatization, and OBO deprotection of diketo OBO-protected carboxylates, using two distinct routes, gives access to valuable α-acyl heteroaromatic compounds.
C. H. A. Esteves, M. Koyioni, K. E. Christensen, P. D. Smith, T. J. Donohoe, Org. Lett., 2018, 20, 4048-4051.
Pd(II)-catalyzed C-C coupling reactions between substituted aliphatic nitriles and arylboronic acids followed by in situ cyclodehydration provide 3-substituted 2-aryl-1H-pyrroles in aqueous acetic acid. This one-pot synthesis is green, and it conforms to atom economy.
M. Yousuf, S. Adhikari, Org. Lett., 2017, 19, 2214-2217.
A copper(II)-catalyzed cyclization reaction of silyl enol ethers derived from methyl ketones with α-diazo-β-ketoesters or α-diazoketones provides 2-siloxy-2,3-dihydrofuran derivatives. These cyclization products serve as versatile 1,4-diketone surrogates, allowing facile in situ preparation of 2,3,5-trisubstituted furans, pyrroles, and thiophenes.
W. W. Tan, N. Yoshikai, J. Org. Chem., 2016, 81, 5566-5573.
An iodine catalyzed C (sp3)-H functionalization of tosylhydrazones with β-enamino esters under visible light irradiation provides tri- and tetra-substituted pyrroles.
N. N. K. Reddy, D. Rawat, S. Adimurthy, J. Org. Chem., 2018, 83, 9412-9421.
An efficient and versatile Pd(II)-catalyzed oxidative three-component cascade reaction of diverse amines, alkyne esters, and alkenes enables the direct synthesis of diverse 2,3,4-trisubstituted pyrroles with broad functional group tolerance and in good to excellent yields.
X. Zhang, X. Xu, G. Chen, W. Yi, Org. Lett., 2016, 18, 4864-4867.
An intramolecular oxidative aza-annulation of enynyl azides provides pyrroles bearing a 2-keto or formyl group via sequential carbon-nitrogen/carbon-oxygen bond formations in the presence of catalytic amounts of AuCl3 and AgSbF6. The required enynyl azides are readily prepared from Morita-Baylis-Hillman (MBH) acetates of acetylenic aldehydes.
C. R. Reddy, S. A. Panda, A. Ramaraju, J. Org. Chem., 2017, 82, 944-949.
Copper iodide catalyzes a sustainable and time economic synthesis of polysubstituted pyrroles in excellent yields with high regioselectivity under mild conditions. The reaction proceedes through imine formation followed by cyclization with an alkyne-Cu intermediate.
M.-H. Hsu, M. Kapoor, T. K. Pradhan, M.-H. Tse, H.-Y. Chen, M.-J. Yan, Y.-T. Cheng, Y.-C. Lin, C.-Y. Hsieh, K.-Y. Liu, C.-C. Han, Synthesis, 2021, 53, 2212-2218.
Pyrrole-2-carbaldehydes can efficiently be prepared from aryl methyl ketones, arylamines, and acetoacetate esters via oxidative annulation and Csp3-H to C=O oxidation in the presence of a copper catalyst, iodine, and oxygen. Mechanistic investigations indicate that the aldehyde oxygen atom originates from oxygen. The reaction avoids the use of stoichiometric quantities of hazardous oxidants.
X. Wu, P. Zhao, X. Geng, C. Wang, Y.-d. Wu, A.-x. Wu, Org. Lett., 2018, 20, 688-691.
A formal [4 + 1] cycloaddition of sulfur ylides with α,β-unsaturated imines followed by an E1cb elimination and an aromatization process provides polysubstituted pyrroles. This protocol offers mild conditions, high efficiency, and a wide substrate scope.
B.-Y. Chen, Y.-N. Wang, T.-R. Li, L.-Q. Lu, W.-J. Xiao, J. You, J. Org. Chem., 2017, 82, 12134-12140.
An efficient, copper-catalyzed [3+1+1] cycloaddition reaction of nitrones and α-acidic isocyanides enables the synthesis of pharmacologically interesting polysubstituted pyrroles. The reaction features wide substrate scope, good functional group tolerance, and operational simplicity.
Z. Tian, J. Xu, B. Liu, Q. Tan, B. Xu, Org. Lett., 2018, 20, 2603-2606.
A Pd-catalyzed annulation of enaminones and alkenes provides various NH-free pyrroles via activation of multiple C(sp2)-H bonds. The evolution of hydrogen has been confirmed by a hydrogen detector.
L. Fu, Y. Liu, J.-P. Wan, Org. Lett., 2021, 23, 4250-4255.
A simple, efficient, cost-effective, and metal-free multicomponent one-pot synthesis with amines, dialkyl acetylenedicarboxylates, and propargylic alcohols afforded fully substituted pyrroles in high yields in three hours using iodine as a catalyst.
N. Bhunia, B. Das, Synthesis, 2013, 45, 1045-1050.
Microwave-promoted iminyl radical cyclizations can be terminated by trapping with TEMPO, affording functionalized adducts without using toxic and hazardous reagents. The use of alkynes as radical acceptors delivers a range of 2-acylpyrroles in good yields.
Y. Cai, A. Jalan, A. R. Kubosumi, S. L. Castle, Org. Lett., 2015, 17, 488-491.
The use 10 mol % of Cu(OTf)2 enables the coupling of α-diazoketones with β-enaminoketones and esters to yield 2,4,5-trisubstituted pyrrole derivatives. A wide range of 2,3-disubstituted indole derivatives were also prepared from α-diazoketones and 2-aminoaryl or alkyl ketones.
B. V. S. Reddy, M. R. Reddy, Y. G. Rao, J. S. Yadav, B. Srighar, Org. Lett., 2013, 15, 464-467.
A range of 2,5-disubstituted and 2,4,5-trisubstituted pyrroles can be synthesized from dienyl azides at room temperature using ZnI2 or Rh2(O2CC3F7)4 as catalysts.
H. Dong, M. Shen, J. E. Redford, B. J. Stokes, A. L. Pumphrey, T. G. Driver, Org. Lett., 2007, 9, 5191-5194.
An electrocyclic ring closure is the key step of an efficient one-pot synthesis of pyrrole-2-carboxylates and -carboxamides from chalcones and glycine esters or amides. The resulting 3,4-dihydro-2H-pyrrole intermediates are oxizided to the corresponding pyrroles by stoichiometric oxidants or by catalytic copper(II) and air in good yields.
D. Imbri, N. Netz, M. Kucukdisli, L. M. Kammer, P. Jung, A. Kretzschmann, T. Opatz, J. Org. Chem., 2014, 79, 11750-11758.
The visible-light-mediated reaction of enamines with α-bromo ketones, with a catalytic amount of Ir(ppy)3, enables the production of various 2,5-diaryl-substituted pyrroles in very good yields. The key intermediates in this reaction are alkyl radicals, generated from single-electron transfer from the photoexcited Ir(ppy)3* to α-bromo ketones, which subsequently react with a broad range of enamines.
T. Lei, W.-Q. Liu, J. Li, M.-Y. Huang, B. Yang, Q.-Y. Meng, B. Chen, C.-H. Tung, L.-Z. Wu, Org. Lett., 2016, 18, 2479-2482.
An efficient, solvent-free, microwave-assisted coupling of chloroenones and amines on the surface of silica gel gave 1,2-disubstituted homochiral pyrroles in good yields.
F. Aydogan, A. S. Demir, Tetrahedron, 2005, 61, 3019-3023.
The CuI/N,N-dimethylglycine-catalyzed reaction of amines with γ-bromo-substituted γ,δ-unsaturated ketones in the presence of K3PO4 and NH4OAc gave the corresponding polysubstituted pyrroles in very good yields.
Y. Pan, H. Lu, Y. Fang, X. Fang, L. Chen, J. Qian, J. Wang, C. Li, Synthesis, 2007, 1242-1246.
A mild, gold(I)-catalyzed acetylenic Schmidt reaction of homopropargyl azides gave regiospecific substituted pyrroles. A mechanism in which azides serve as nucleophiles toward gold(I)-activated alkynes with subsequent gold(I)-aided expulsion of dinitrogen is proposed.
D. J. Gorin, N. R. Davis, F. D. Toste, J. Am. Chem. Soc., 2005, 127, 11260-11261.
A mild, gold(I)-catalyzed cycloisomerization of β-allenylhydrazones provides an efficient access to multisubstituted N-aminopyrroles in good to excellent yields with short reaction times through a selective intramolecular 1,2-alkyl or -aryl migration. This intramolecular cyclization can be applied either to alkyl- or aryl-substituted allenes.
E. Benedetti, G. Lemière, L.-L. Chapellet, A. Penoni, G. Palmisano, M. Malacria, J.-P. Goddard, L. Fensterband, Org. Lett., 2010, 12, 4396-4399.
A one-step reaction to assemble pyrroles from α,β-unsaturated imines and acid chlorides is mediated by triphenylphosphine, which eliminates phosphine oxide to allow cyclization. This reaction has been employed to access broad range of pyrroles via modulation of the two building blocks and applied as well to the synthesis of lukianol A.
Y. Lu, B. A. Arndtsen, Org. Lett., 2009, 11, 1369-1372.
An unprecedented nucleophilic addition/cyclization/aromatization cascade of simple starting materials, i.e., aromatic alkenes/alkynes, trimethylsilyl cyanide and N,N-disubstituted formamide provides multisubstituted pyrroles in good yields with high regioselectivities.
X.-Q. Mou, Z.-L. Xu, L. Xu, S.-H. Wang, B.-H. Zhang, D. Zhang, J. Wang, W.-T. Liu, W. Bao, Org. Lett., 2016, 18, 4032-4035.
An iron(III)-catalyed four-component coupling reaction of 1,3-dicarbonyl compounds, amines, aromatic aldehydes, and nitroalkanes without an inert atmosphere provides highly substituted pyrroles in good yields. Notably, this method is very cheap, straightforward, and environmentally friendly compared to existing methods.
S. Maiti, S. Biswas, U. Jana, J. Org. Chem., 2010, 75, 1674-1683.
The FeCl3-catalyzed addition and cyclization of enamino esters with nitroolefins provides a rapid, straightforward, and general method for the synthesis of tetrasubstituted NH pyrroles in good yields and tolerates a wide range of functionality. Further, an efficient KOAc-promoted addition and cyclization protocol provides substituted furans as well.
L. Li, M.-N. Zhao, Z.-H. Ren, J. Li, Z.-H. Guan, Synthesis, 2012, 44, 532-540.
A fast, mild, and environmentally benign domino reaction enables an efficient reaction of (E)-β-bromonitrostyrenes with enaminones in water to afford pyrroles in excellent yields.
M. Rueping, A. Parra, Org. Lett., 2010, 12, 5281-5283.
An efficient rhodium-catalyzed rearrangement of α-oximino ketenes derived from α-diazo oxime ethers provides 2H-azirines bearing quaternary centers and allows for subsequent rearrangement to highly substituted pyrroles in excellent yields.
Y. Jiang, W. C. Chan, C.-M. Park, J. Am. Chem. Soc., 2012, 134, 4104-4107.
A cationic N-heterocyclic carbene-gold(I) complex catalyzes the formation of tri- and tetrasubstituted pyrroles from N-propargyl β-enaminone derivatives via an amino-Claisen rearrangement to yield α-allenyl β-enaminones and subsequent cyclization of these intermediates.
A. Saito, O. Konishi, Y. Hanzawa, Org. Lett., 2010, 12, 372-374.
N-Propargylic β-enaminones are common intermediates for the synthesis of polysubstituted pyrroles and pyridines. In the presence of Cs2CO3 N-propargylic β-enaminones are cyclized to pyrroles in good to high yields, whereas CuBr leads to pyridines.
S. Cacchi, G. Fabrizi, E. Filisti, Org. Lett., 2008, 10, 2629-2632.
A Cu(OAc)2-promoted oxidation/[3+2]cycloaddition/aromatization cascade reaction provides tetrasubstituted NH-pyrroles in very good yields from a wide range of chalcones and diethyl iminodiacetates. This convenient methodology has several advantages, such as the use of easily accessible chalcones and readily available diethyl iminodiacetates, and mild reaction conditions.
Z.-q. Lin, C.-d. Li, Z.-c. Zhou, S. Xue, J.-r. Gao, Q. Ye, Y.-j. Li, Synlett, 2019, 30, 1442-1446.
An operationally simple organocatalytic method generates a chiral tertiary/quaternary stereocenter at the C3 position of pyrroles. The process proceeds through an amine-catalyzed direct aldol reaction of succinaldehyde with various acceptor carbonyls, followed by a Paal-Knorr reaction with a primary amine in the same pot.
A. P. Pawar, J. Yadav, A. J. Dolas, Y. K. Nagare, E. Iype, K. Rangan, I. Kumar, Org. Lett., 2022, 24, 7549-7554.
Various 2-alkyl-5-aryl-(1H)-pyrrole-4-ol derivatives were synthesized via a multicomponent reaction of β-dicarbonyl compounds with arylglyoxals in the presence of ammonium acetate in water at room temperature.
B. Khalili, P. Jajarmi, B. Eftekhari-Sis, M. M. Hashemi, J. Org. Chem., 2008, 73, 2090-2095.
The Blaise reaction intermediate, generated in situ from Reformatsky reagent and nitrile, reacts with arylglyoxals chemoselectively to afford a wide variety of substituted NH-pyrroles in good yields.
Z. Chen, H. Chen, X. Yang, X. Chang, Synlett, 2017, 28, 1463-1466.
An efficient and regioselective palladium-catalyzed cyclization of internal alkynes and 2-amino-3-iodoacrylates gave good yields of highly functionalized pyrroles.
M. L. Crawley, I. Goljer, D. J. Jenkins, J. F. Mehlmann, L. Nogle, R. Dooley, P. E. Mahaney, Org. Lett., 2006, 8, 5837-5840.
In(OTf)3 or In(NTf2)3 effectively catalyze the cycloisomerization reaction of α-propargyl-β-keto esters and their imine analogues to afford trisubstituted furans and pyrroles, respectively. Both terminal and internal alkynes take part in the reaction with good functional-group compatibility in the presence of only a small catalyst loading.
H. Tsuhi, K.-i. Yamagata, Y. Ueda, E. Nakamura, Synlett, 2011, 1015-1017.
A Mn(III)-catalyzed reaction of vinyl azides with 1,3-dicarbonyl compounds gave a broad range of polysubstituted N-H pyrroles in good yields.
Y.-F. Wang, K. K. Toh, S. Chiba, K. Narasaka, Org. Lett., 2008, 10, 5019-5022.
Two methods for the regioselective synthesis of tetra- and trisubstituted N-H pyrroles from starting vinyl azides have been developed: A thermal pyrrole formation via the 1,2-addition of 1,3-dicarbonyl compounds to 2H-azirine intermediates generated in situ from vinyl azides and a Cu(II)-catalyzed synthesis with ethyl acetoacetate through a 1,4-addition.
S. Chiba, Y.-F. Wang, G. Lapointe, K. Narasaka, Org. Lett., 2008, 10, 313-316.
Tetrasubstituted pyrroles can be synthesized in a one-pot procedure from isoxazoles via photoinduced in situ formation of acylazirines combined with a subsequent cobalt(II)-catalyzed ring expansion with 1,3-diketones.
S. Pusch, D. Kowalczyk, T. Opatz, J. Org. Chem., 2016, 81, 4170-4178.
A three-component reactions of arylacyl bromides, amines, and dialkyl acetylenedicarboxylate in the presence of iron(III) chloride as a catalyst at room temperature afforded polysubstituted pyrroles in high yields.
B. Das, G. C. Reddy, P. Balasubramanyam, B. Veeranjaneyulu, Synthesis, 2010, 1625-1628.
A one-pot sequential 1,3-dipolar cycloaddition/aromatization reaction sequence enables the synthesis of multisubstituted pyrroles from simple, easy available alkenes. A well-defined silver-catalyzed 1,3-dipolar cycloaddition reaction is followed by a benzoyl peroxide-mediated oxidative dehydrogenative aromatization reaction.
Y. Liu, H. Hi, X. Wang, S. Zhi, Y. Kan, C. Wang, J. Org. Chem., 2017, 82, 4194-4202.
A simple, efficient, cost-effective, and metal-free four-component coupling reaction of aldehydes, amines, dialkyl acetylenedicarboxylates, and nitromethane furnished the corresponding 1,2,3,4-tetrasubstituted pyrroles under reflux in the presence of molecular iodine as a catalyst in high yields within 8 hours.
B. Das, N. Bhunia, M. Lingaiah, Synthesis, 2011, 3471-3474.
A new and efficient three-component reaction between dialkyl acetylenedicarboxylates, aromatic amines, triphenylphosphine, and arylglyoxals afforded polysubstituted pyrrole derivatives in high yields. The reactions were performed in dichloromethane at room temperature and under neutral conditions.
M. Anary-Abbasinejad, K. Charkhati, H. Anaraki-Ardakani, Synlett, 2009, 1115-1117.
A reaction between dialkyl acetylenedicarboxylates and β-aminoketones promoted by triphenylphosphine allows an efficient one-pot synthesis of polysubstituted 2,5-dihydropyrrole derivatives. The prepared 2,5-dihydropyrroles can be easily oxidized to the corresponding pyrrole derivatives with chromium trioxide.
M. Anary-Abbasinejad, E. Poorhassan, A. Hassanabadi, Synlett, 2009, 1929-1932.
A basic functionalized ionic liquid, 1-butyl-3-methylimidazolium hydroxide ([bmim]OH), catalyzed the three-component condensation reaction of acid chlorides, amino acids, and dialkyl acetylenedicarboxylates in water to afford functionalized pyrroles in high yields.
I. Yavari, E. Kowsari, Synlett, 2008, 897-899.
The combination of I2/PhI(OAc)2 promotes an efficient and practical one-pot reaction of amines with alkyne esters and chalcones under solvent-free ball-milling conditions to afford a variety of polysubstituted trans-2,3-dihydropyrroles in good yields. This protocol furnishes the corresponding pyrroles with the addition of DDQ as oxidant in a subsequent step.
H. Xu, H.-W. Liu, K. Chen, G.-W. Wang, J. Org. Chem., 2018, 83, 6035-6049.
A iodine-catalyzed tandem Michael addition/oxidative annulation of allenes and enamines provides polysubstituted pyrroles in an efficient and highly regioselective way in good yields under mild conditions.
Y. Wang, C.-M. Jiang, H.-L. Li, F.-S. He, X. Luo, W.-P. Deng, J. Org. Chem., 2016, 81, 8653-8658.
The reaction of an enaminone, which can be derived from two primary amines and diketene, in the presence of nitrostyrene gives functionalized pyrrole derivatives in very good yields.
A. Alizadeh, A. Rezvanian, H. R. Bijanzadeh, Synthesis, 2008, 725-728.
A silver(I)-promoted oxidative cyclization of homopropargylamines at room temperature provides pyrroles. Homopropargylamines are readily available by the addition of a propargyl Grignard reagent to Schiff bases.
S. Aggarwal, H.-J. Knölker, Org. Biomol. Chem., 2004, 2, 3060-3062.
A general, highly flexible Cu-catalyzed domino C-N coupling/hydroamination reaction constitutes a straightforward alternative to existing methodology for the preparation of pyrroles and pyrazoles.
R. Martin, M. R. Rivero, S. L. Buchwald, Angew. Chem. Int. Ed., 2006, 45, 7079-7082.
An efficient and simple palladium(II)-catalyzed cascade reaction of 2-(2-oxo-2-arylethyl)malononitriles with boronic acids provides substituted 1H-pyrrole-3-carbonitriles via C(sp)-C(sp2) coupling followed by intramolecular C-N bond formation.
Z. Wang, W. Chen, H. Luo, C. He, G. Zhang, Y. Yu, Synthesis, 2020, 52, 1659-1665.
An efficient and highly versatile microwave-assisted Paal-Knorr condensation of various 1,4-diketones gave furans, pyrroles and thiophenes in good yields. In addition, transformations of the methoxycarbonyl moiety, such as Curtius rearrangement, hydrolysis to carboxylic acid, or the conversion into amine by reaction with a primary amine in the presence of Me3Al, are described.
G. Minetto, L. F. Raveglia, A. Sega, M. Taddei, Eur. J. Org. Chem., 2005, 5277-5288.
A direct synthesis of pyrroles from imines, acid chlorides, and alkynes mediated by isocyanides proceeds with a range of substrates, providing a method to generate various pyrroles in high yield. Mechanistic studies suggest a generation of imino analogues of münchnones, which can undergo in situ coupling with alkynes to liberate isocyanate and form the pyrrole product.
D. J. St. Cyr, N. Martin, B. A. Arndtsen, Org. Lett., 2007, 9, 449-452.
The nucleophilic addition of sodium azide to 1,2-allenyl esters regio- and stereoselectively generates vinyl azides in excellent yields. A sequential reaction for the synthesis of pyrroles using 1-allyllic 1,2-allenyl esters as substrates is developed on the basis of a domino process involving nucleophilic addition, cycloaddition, denitrogenation, and aromatization.
X. Huang, R. Shen, T. Zhang, J. Org. Chem., 2007, 72, 1534-1537.
The synthesis of N-acylpyrroles from primary aromatic amides and excess 2,5-dimethoxytetrahydrofuran in presence of one equivalent of thionyl chloride offers short reaction times, mild reaction conditions, and easy workup.
A. R. Ekkati, D. K. Bates, Synthesis, 2003, 1959-1961.
Propargyl vinyl ethers and aromatic amines are effectively converted into tetra- and pentasubstituted 5-methylpyrroles through a silver(I)-catalyzed propargyl-Claisen rearrangement, an amine condensation, and a gold(I)-catalyzed 5-exo-dig heterocyclization in a convenient one-pot process.
J. T. Binder, S. F. Kirsch, Org. Lett., 2006, 8, 2151-2153.
Various 2,3,4-trisubstituted pyrroles are easily accessible in one step from readily available acetylenes and acceptor-substituted methyl isocyanides by base-mediated or copper-catalyzed cycloadditions. Scope and limitations of both pyrrole syntheses are discussed.
O. V. Larionov, A. de Meijere, Angew. Chem. Int. Ed., 2005, 44, 5664-5667.
A highly efficient amidation reaction of heterocycles with N-fluorobenzenesulfonimide (NFSI) presumably proceedes via C-H bond activation in the presence of cuprous iodide as catalyst. Various α-amidated heterocycle derivatives have been generated in good to excellent yields.
S. Wang, Z. Ni, X. Huang, J. Wang, Y. Pan, Org. Lett., 2014, 16, 5648-5651.
A gold-catalyzed intermolecular ynamide amination-initiated aza-Nazarov cyclization enables a facile and efficient synthesis of various 2-aminopyrroles in good yields. High flexibility, broad substrate scope, and mild nature of this reaction render it a viable alternative for the construction of 2-aminopyrroles.
C. Shu, Y.-H. Wang, C.-H. Shen, P.-P. Ruan, X. Lu, L-W. Ye, Org. Lett., 2016, 18, 3254-3257.
An effective and mild gold-catalyzed intermolecular nitrene transfer by the reaction of 2H-azirines and ynamides provides highly substituted pyrroles in a straightforward manner in very good yields. Preliminary results indicate that a nongold carbenoid pathway is preferred.
L. Zhu, Y. Yu, Z. Mao, X. Huang, Org. Lett., 2015, 17, 30-33.
A gold-catalyzed intermolecular reaction of vinyl azides and ynamides enables an efficient and mild approach to multisubstituted 2-aminopyrroles in very good yields.
Y. Wu, L. Zhu, Y. Yu, X. Luo, X. Huang, J. Org. Chem., 2015, 80, 11407-11416.
A rhodium(II)-catalyzed formal [3 + 2] cycloaddition of N-sulfonyl-1,2,3-triazoles with isoxazoles provides polysubstituted 3-aminopyrrole derivatives. An operationally simple one-pot synthesis of the titled compounds from terminal alkynes, tosyl azide, and isoxazoles was also developed.
X. Lei, L. Li, Y.-P. He, Y. Tang, Org. Lett., 2015, 17, 5224-5227.
A multicomponent domino reaction of readily available isocyanides, primary or secondary amines, and gem-diactivated olefins enables a chemoselective, catalyst-free synthesis of structurally diverse, polysubstituted pyrroles in good yields under mild conditions.
X. Wang, X.-P. Xu, S.-Y. Wang, W. Zhou, S.-J. Ji, Org. Lett., 2013, 15, 4246-4249.
Tetrasubstituted/functionalized NH-pyrroles can be synthesized from gem-diactivated acrylonitriles and TMSCN. The strategy utilizes the generation of vic-dinitrile via Michael addition and cyanide-mediated nitrile-to-nitrile cyclocondensation.
S. K. Guchhait, S. Sisodiya, M. Saini, Y. V. Shah, G. Kumar, D. P. Daniel, N. Hura, V. Chaudhary, J. Org. Chem., 2018, 83, 5807-5815.
A novel and efficient multicomponent reaction of N-tosylimines, DMAD, and isocyanides for the synthesis of 2-aminopyrrole systems was uncovered.
V. Nair, A. U. Vinod, C. Rajesh, J. Org. Chem., 2001, 66, 4427-4429.
A Au(I)-catalyzed hydroamination or hydration of 1,3-diynes allows access to 2,5-diamidopyrroles and 2,5-diamidofurans. This method can also be expanded to 2,5-disubstituted furans and 1,2,5-trisubstituted pyrroles.
S. Kramer, J. L. H. Madsen, M. Rottländer, T. Skrydstrup, Org. Lett., 2010, 12, 2758-2761.
A robust and operational simple route to 2,4-disubstituted pyrrole heterocycles relying upon a cascade reaction is air and moisture tolerant and is performed at ambient temperature. Control over the reaction conditions provides ready access to isopyrroles, 2,3,4-trisubstituted pyrroles and 3-substituted pyrollidin-2-ones.
B. M. Trost, J.-P. Lumb, J. M. Azzarelli, J. Am. Chem. Soc., 2011, 133, 740-743.
A new microwave-assisted rearrangement of 1,3-oxazolidines scaffolds is the basis for a new, metal-free, direct, and modular construction of tetrasubstituted pyrroles from terminal-conjugated alkynes, aldehydes, and primary amines under very simple and environmental-friendly experimental conditions.
D. Tejedor, D. González-Cruz, F. García-Tellado, J. J. Marrero-Tellado, M. L. Rodríguez, J. Am. Chem. Soc., 2004, 126, 8390-8391.
Coupling of acetylene, nitrile, and a titanium reagent generated new azatitanacyclopentadienes in a highly regioselective manner. The subsequent reaction with sulfonylacetylene and electrophiles gave substituted pyridines virtually as a single isomer. Alternatively, the reaction of azatitanacyclopentadienes with an aldehyde or another nitrile gave furans or pyrroles having four different substituents again in a regioselective manner.
D. Suzuki, Y. Nobe, R. Tanaka, Y. Takayama, F. Sato, H. Urabe, J. Am. Chem. Soc., 2005, 127, 7474-7479.
An efficient synthesis of 2,3,4-trisubstituted pyrroles via intermolecular cyclization of alkylidenecyclopropyl ketones with amines was observed. A mechanism involving a distal cleavage of the C-C bond of the cyclopropane ring is discussed.
L. Lu, G. Chen, S. Ma, Org. Lett., 2006, 8, 835-838.
Several aryl-substituted pyrrole derivates were prepared conveniently in a microwave-assisted one pot-reaction from but-2-ene-1,4-diones and but-2-yne-1,4-diones via Pd/C-catalyzed hydrogenation of the carbon-carbon double bond/triple bond followed by amination-cyclization.
H. S. P. Rao, S. Jothilingam, H. W. Scheeren, Tetrahedron, 2004, 60, 1625-1630.
1,3,4-triaryl-2,5-dihydropyrroles were synthesized using the McMurry coupling reaction as key step. A facile and reliable non-catalytic photoconversion of 1,3,4-triaryl-2,5-dihydropyrroles furnished 1,3,4-triarylpyrroles in good yields.
D. X. Zeng, Y. Chen, Synlett, 2006, 490-492.
1-Vinylpyrroles are formylated by the N,N-dimethylformamide/oxalyl chloride reagent system to give the corresponding 1-vinylpyrrole-2-carbaldehydes in good yields in short reaction times.
A. I. Mikhaleva, A. V. Ivanoc, E. V. Skital'tseva, I. A. Ushakov, A. M. Vasil'tsov, B. A. Trofimov, Synthesis, 2009, 587-590.
A series of substituted 3-trifluoromethylpyrroles was obtained in good yield from trifluoromethylamino-ynol derivatives via mesylation and a gold-catalyzed cyclization under mild conditions.
B. Guieu, M. Le Roch, M. David, N. Gouault, J. Org. Chem., 2017, 82, 13708-13713.
A sequential intermolecular hydroamination reaction of 2-trifluoromethyl-1,3-enynes with aliphatic primary amines under mild reaction conditions followed by a NXS mediated oxidative cyclization of the hydroamination product provides halogenated trifluoromethylated pyrroles. This method offers mild conditions, high efficiency, readily available starting materials, general substrate scope, and synthetic utility of the products.
C. Huang, Y. Zeng, H. Cheng, A. Hu, L. Liu, Y. Xiao, J. Zhang, Org. Lett., 2017, 19, 4968-4971.
A silver-catalyzed cyclization of vinyl azides with ethyl 4,4,4-trifluoro-3-oxobutanoate provides highly substituted 2-trifluoromethyl pyrroles. Various α-(heteo)aryl, alkyl, β-aryl, as well as α,β-disubstituted vinyl azides participate in this regioselective transformation.
W. Wu, S. Wen, X. Zhang, Q. Lin, Z. Weng, Org. Lett., 2021, 23, 6352-6356.
tert-Butyl nitrite promotes an oxidative metal-free intermolecular sulfonamination of alkynylamines with sulfinic acids to provide substituted sulfonyl pyrroles via tandem addition/cyclization. Various substituted sulfonyl pyrroles are formed in good yields.
Z. Qi, Y. Jiang, Y. Wang, R. Yan, J. Org. Chem., 2018, 83, 8607-8614.