A facile synthesis of 1-aryl pyrroles by Clauson-Kaas reaction using oxone as a Catalyst under microwave irradiation (original) (raw)
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Microwave-activated Synthesis of Pyrroles: A Short Review
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A Mild and Facile One-Pot Synthesis of N-Methyl-3-Acyl-Pyrroles
Molecules, 2010
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Microwave assisted synthesis of pyrroles
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The synthesis of pyrroles by reaction of hexane-2,5-dione with primary amines has been shown to occur in less than 2 minutes under microwave activation. © 1999 Elsevier Science Ltd. All rights reserved.
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Nitrogen containing heterocyclic compounds are biologically significant molecules. This is especially true for pyrrole a five membered nitrogen containing aromatic molecule, which is present as a key structural motif in a large number of drugs and lead molecules. This review aims to provide an overview of the multi-component reaction (MCR) based methodologies used for the synthesis of pyrrole and its derivatives, focusing particularly on eco-friendly methods that avoid the use of hazardous reagents, solvents and catalysts are deemed especially relevant to the disciplines of medicinal chemistry and drug discovery.
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Pyrrole is widely known as a biologically active scaffold which possesses a diverse nature of activities. The combination of different pharmacophores in a pyrrole ring system has led to the formation of more active compounds. Pyrrole containing analogs are considered as a potential source of biologically active compounds that contains a significant set of advantageous properties and can be found in many natural products. The present review highlights the synthetic methods of representatives of nitrogen heterocycles such as pyrrole, substituted pyrroles and other related compounds. The aim of this review is to indicate and summarise the different methods for the synthesis of nitrogen containing heterocycles from the group of pyrrole and pyrrole related structures.
ChemistrySelect, 2018
The synthesis of pyrroles under mild conditions using sulfonic acid-functionalized β-Cyclodextrin (β-CD) as a supramolecular catalyst under aqueous conditions is demonstrated. Good to excellent conversion of various amines into pyrroles was observed without any side product formation. CD was found to play a dual role as a phase transfer reagent through inclusion as well as an acid catalyst thereby facilitating the smooth conversions of reactants. The advantages of this protocol are mild reaction conditions, sustainable catalyst and use of nontoxic solvent water. Notably, the catalyst can be easily recovered and reused up to five cycles without any loss of catalytic activity. The developed protocol was successfully used as a key step for the formal synthesis of the alkaloid natural product Polygonatine. Pyrrole is a five membered heterocyclic motif which is most commonly found in biologically active molecules, natural products and drugs. [1] Several of its derivatives/natural products show antibacterial, antiviral, anti-inflammatory, anti-tumoral, and antioxidant activities [2] (a few illustrated in Figure 1). Owing to their importance, a plethora of methods/reactions are available in literature for the synthesis of pyrroles, including the more popular reactions such as Paal-Knorr, [3] Clauson-Kaas, [4] Hantzsch process, [5] and several other methods such as conjugate addition reactions, [6] transition metal-mediated reactions, [7] reductive couplings, [8] Aza-Wittig, [9] as well as multicomponent reactions. [10] Amongst these, Clauson-Kaas and Paal-Knorr are most commonly used reactions for the synthesis of pyrroles as they use simple and readily available precursors. These reactions were reported with several catalysts such as Ionic liquid, [11] zeolite, [12] Sc(OTf) 3 , [13] Ti(OiPr) 4 , [14] Al 2 O 3 , [15] Bi (NO 3) 3 , [16] Yb(OTf) 3 , [17] CoCl 2 , [18] InCl 3 , [19] RuCl 3 , [20] montmorillonite-KSF, [21] sulfamic acid, [22] SnCl 2 ⋅2H 2 O, [23] silica sulfuric acid, [24] microwave, [25] P 2 O 5 , [26] CuCl 2 , [27] FeCl 3 .7H 2 O, [28] montmorillonite K-10, [29] CeCl 3 , [30] Bi(NO 3) 3 .5H 2 O, [31] MgI 2 Et 2 O, [32] I 2 , [33] Cyclodextrin, [34] ultrasound irradiation, [35] nano-organocatalyst, [36] Amberlite IR 120, [37] Pr(OTf) 3 , [38] and PEG-SO 3 H. [39] Despite the advances, many of them suffer from certain drawbacks such as harsh reaction conditions, use of expensive reagents, toxic solvents, strongly acidic conditions, costly catalysts, longer reaction times, non-recyclability, involve tedious workup procedures and use extra energy sources such as microwaves or ultrasound. Therefore, in this context, the development of an efficient, simple, economical, and environmentally friendly protocol using a recyclable catalyst and a green solvent for the synthesis of N-substituted pyrrole derivatives is highly desirable.