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2020

Ultrasound assisted rapid synthesis of mefenamic acid based indole derivatives under ligand free Cu-catalysis: Their pharmacological evaluation

An improved and rapid synthesis of mefenamic acid based indole derivatives has been achieved via the ligand free Cu-catalyzed coupling-cyclization method under ultrasound irradiation. This simple, straightforward and inexpensive one-pot method involved the reaction of a terminal alkyne derived from mefenamic acid with 2- iodosulfanilides in the presence of CuI

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Base mediated spirocyclization of quinazoline: one-step synthesis of spiro-isoindolinone dihydroquinazolinones

A novel approach for the spiro-isoindolinone dihydroquinazolinones has been demonstrated from 2- aminobenzamide and 2-cyanomethyl benzoate in the presence of KHMDS as a base to get moderate yields. The reaction has been screened in various bases followed by solvents and a gram scale reaction has also been executed under the given conditions. Based on the controlled experiments a plausible reaction mechanism has been proposed. Further the substrate scope of this reaction has also been studied.

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2019

Formal synthesis of Cladospolide C & epi-Cladospolide C using R- (þ)-g-valerolactone as a chiral synthon

The formal synthesis of Cladospolide-C and its analog is achieved by using enantiopure (R)-g evalerolactone 10. The significant points of this synthesis are the stereoselective dihydroxylation of a, bunsaturated ester 16 using Sharpless protocol, Wittig olefination of g evalerolactol 6 with triphenylphosphonium iodide salt 7, one pot selective oxidation

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2018

Amberlite-15 promoted an unprecedented aza Michael rearrangement for one pot synthesis of dihydroquinazolinone compounds

A new one pot multicomponent annulation strategy for the synthesis of various dihydroquinazolinone compounds has been developed using Amberlite-15 as a catalyst, giving good to moderate yields. In this reaction the substrate scope for amines and aldehydes was also investigated. The reaction has been checked on a large scale

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2017

Synthesis of (+)-Patulolide C Using R-(+)-g-Valerolactone as a Chiral Synthon.

The total synthesis of (+)-Patulolide-C is accomplished by using enantiopure R-(+)-g-valerolactone & R-(+)-epichlorohydrin as chiral synthons. The strategy adopted for the synthesis is a convergent approach wherein two advanced intermediates were synthesized independently using the chiral synthons and coupled to achieve the skeleton of Patulolide-C. The important synthetic steps of the synthesis are two carbon homologation of the cyclic lactol, Julia olefination of enone with sulfone in DME, DIBAl-H mediated regioselective opening of benzylidine acetal, selective oxidation of primary alcohol to aldehyde using BAIB/TEMPO and lactonization of seco-acid adopting Yamaguchi protocol to afford the macrolide skeleton.

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A diastereoselective synthesis of boceprevir's gem-dimethyl bicyclic [3.1.0] proline intermediate from an insecticide ingredient ciscypermethric acid

An efficient multi-gram synthesis of (1R,2S,5S)-methyl 6,6-dimethyl-3-azabicyclo[3.1.0]hexane-2- carboxylate, a key chiral bicyclic proline fragment employed in the construction of the potent antiHCV drug boceprevir, has been presented. The synthetic route commences with the readily available cis-cypermethric acid, a cheap source of the cyclopropane ring required in the targeted compound, and utilizes the cis-orientation of the 2,2-dichlorovinyl and carboxylic acid side arms, already present in the starting material, to effect a diastereoselective construction of the proline moiety

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A convergent approach towards the synthesis of the 2-alkylsubstituted tetrahydroquinoline alkaloid ()-cuspareine

A convergent approach towards the synthesis of the 2-alkyl-substituted tetrahydroquinoline alkaloid ()-cuspareine via enantiospecific construction of the (R)-benzyl 2-formyl-3,4-dihydroquinoline-1(2H)- carboxylate. We have achieved an efficient enantiospecific synthesis of ()-cuspareine starting from known key starting materials. The reactions employed for individual transformations are simple and high yielding, and the strategy could potentially be easily extended.

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2016

A cascade reaction for the new and direct synthesis of indolofuroquinoxalines

The 7H-indolo[30 ,20 :4,5]furo[2,3-b]quinoxaline derivatives are synthesized directly from methyl 2-(2- chloro-1H-indol-3-yl)-2-oxoacetate or its N-alkyl derivatives under neutral or mildly acidic conditions. This new one-pot methodology was found to be general and greener as it avoids the use of environmentally harmful POCl3 and strong alkali required for the previously reported method. It is also amenable for scale-up.

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A concise stereoselective synthesis of (+)-1-deoxy-6-epicastanospermine

A concise stereoselective synthesis of (+)-1-deoxy-6-epi-castanospermine has been developed through stereoselective approach from the chiral precursor R-Glycidol. The key steps in the synthesis involve Grignard reaction through Weinreb amide, followed by Sharpless dihydroxylation and stereoselective reduction of imine assigned the required stereochemical feature of indolizidine azasugar (+)-1-deoxy6-epi-castanospermine.

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Synthesis of 2-hydroxy-3-alkyl-2-phenyl-2,3- dihydroquinazolin-4(1H)-one via molybdenum hexacarbonyl mediated CO gas- and ligand free carbonylative reactions

Carbon monoxide gas and ligand-free conditions were developed for the synthesis of 2-hydroxy-3-alkyl-2-phenyl-2,3-dihydroquinazolin4(1H)-one via catalytic carbonylation with molybdenum hexacarbonyl as an efficient carbonylating agent for the three-component reaction of isatoic anhydride, amine, iodobenzene. Mo(CO)6 is a solid carbon monoxide source. The quinazolinone synthesis proceeds via a sequential series of reactions such as nucleophilic attack of the amine group on the carbonyl group of isatoic anhydride followed by ring opening, subsequent decarboxylation, carbonylation and heterocyclization.

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Stereoselective synthesis of (R)-() and (S)-(+)-phoracantholide I from (R)-(+)-c-valerolactone

A concise total synthesis of (R)-()-phoracantholide I 1 and (S)-(+)-phoracantholide I 2 has been developed from (R)-(+)-c-valerolactone 6. The key steps in the synthesis of these macrolides involved enzymatic reduction of Levulinic ester 4 by asymmetric dehydrogenase, Z-selective Wittig reaction of (4-carboxybutyl)triphenylphosphonium ylide 11 with lactol 7, and cyclization of seco-acid 8 using either a Yamaguchi lactonization protocol or a Mitsunobu protocol to afford (R)-()-phoracantholide I and (S)-(+)-phoracantholide I respectively

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An efficient and convenient protocol for the synthesis of tetracyclic isoindolo[1,2-a]quinazoline derivatives

A convenient and one-pot synthesis of tetracyclic isoindolo [1,2-a]quinazoline derivatives via Lewis acid mediated sequential C–N bond formation reactions is reported. This protocol provides a simple and rapid strategy for the synthesis of 12-benzylidene-10,12-dihydroisoindolo[1,2-b]quinazoline derivatives. However, a variety of tetracyclo indole fused quinazoline motifs were synthesized in good yields.

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Concise and highly stereoselective syntheses of D-fagomine and 2-epi-fagomine

Highly stereoselective total syntheses of polyhydroxylated piperidines D-fagomine and 2-epi-fagomine have been developed starting from 3,4,6-tri-O-benzyl-D-glucal which is a derivative of D-Glucose. Key steps in the synthesis of these azasugars involved N-Boc-protected amine preparation from oxime followed by stereo specific iodination of alcohol and cascade cyclization triggered by N-Boc deprotection

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A new strategy for accessing (S)-1-(furan-2-yl)pent-4-en-1-ol: a key precursor of Ipomoeassin family of compounds and C1–C15 domain of halichondrins

A highly efficient synthesis of (S)-1-(furan-2-yl)pent-4-en-1-ol, known to be an initial precursor of Ipomoeassin family of compounds and C1–C15 domain of halichondrins has been achieved via a sequence involving the use of Weinreb amide formation followed by Weinreb ketone synthesis and finally CBS (Corey–Bakshi–Shibata) reduction. Detailed study on improvement of each step is described. The title compound was converted to a potential cytotoxic agent for further pharmacological studies

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A Simple Approach for the Synthesis of Fused Quinazoline-Based Tetracyclic Compounds via a Multicomponent Reaction Strategy

A simple method for the synthesis of tetracyclic quinazolinone derivatives via a multicomponent reaction strategy from isatoic anhydride and amine with ninhydrin has been developed.

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FeF3-catalyzed MCR in PEG-400: ultrasound assisted synthesis of N-substituted 2- aminopyridines

FeF3 catalyzed four component reaction under ultrasound irradiation was explored for the first time to prepare N-substituted 2-aminopyridines in good yields. The methodology involved the use of readily available starting materials and PEG-400 under mild reaction conditions in the presence of air. The one-pot methodology afforded a range of compounds of pharmacological interest indicating its potential in generating a diversity based library of small molecules useful for medicinal chemistry and drug discovery

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Development of a Chemoenzymatic Process for Dehydroepiandrosterone Acetate Synthesis

Dehydroepiandrosterone (DHEA, 2) is an important endogenous steroid hormone in mammals used in the treatment of a variety of dysfunctions in female and male health,1 as well as an intermediate in the synthesis of steroidal drugs, such as abiraterone acetate which is used for the treatment of prostate cancer.2−4 In this manuscript we describe a novel, concise, and cost-efficient route toward DHEA (2) and DHEA acetate (3) from 4-androstene-3,17-dione (4-AD, 1). Crucial to success was the identification of a ketoreductase from Sphingomonas wittichii for the highly regio- and stereoselective reduction of the C3- carbonyl group of 5-androstene-3,17-dione (5) to the required 3β-alcohol (2, >99% de). The enzyme displayed excellent robustness and solvent stability under high substrate concentrations (up to 150 g/L).

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2015

A short diastereoselective synthesis of cis-(2S,4S) and cis-(2R,4R)-4- hydroxyprolines

A concise synthesis of (2R,4R)-4-hydroxyproline (1) and (2S,4S)-4-hydroxyproline (2) has been developed in enantiomerically pure form from commercially available starting materials with excellent diastereoselectivity. The tightly bound chelation controlled transition state formed during the 5-exo-tet ring closure reaction is assumed to be the origin of high diastereoselectivity.

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Sulfonic acid functionalized Wang resin (Wang-OSO3H) as polymeric acidic catalyst for the eco-friendly synthesis of 2,3-dihydroquinazolin-4(1H)-ones

An efficient and green approach has been developed for the synthesis of 2-substituted 2,3-dihydroquinazolin-4(1H)-ones directly from corresponding substituted aromatic and aliphatic aldehyde and anthranilamide using recyclable polymer supported sulfonic acid catalyst under aqueous conditions. Environmental acceptability, operational simplicity, low cost, excellent functional group compatibility, and high yields are the important features of this protocol.

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An efficient one pot synthesis of 2-amino quinazolin-4(3H)-one derivative via MCR strategy

A novel multi-component reaction strategy was developed for the construction of important building blocks, 2-amino 3-substituted quinazolinone derivatives from isatoic anhydride and amine with electrophilic cyanating compound, N-cyano-4-methyl-N-phenylbenzenesulfonamide (NCTS). The quinazolinone synthesis proceeds via a sequential series of reactions such as nucleophilic attack of the amine group on the carbonyl group of isatoic anhydride followed ring opening and subsequent decarboxylation, nucleophilic attack of amine to nitrile, followed by heterocyclization.

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Diastereoselective total synthesis of piperidine alkaloids: (2R,5R)- 5-hydroxyhomopipecolic acid and (2R,5R,8R)-5-hydroxysedamine

Total synthesis of 2,5-disubstituted piperidine alkaloids, 5-hydroxyhomopipecolic acid (1) and 5-hydroxysedamine (2) was accomplished in overall high yields with a high level of 1,4-asymmetric induction. The ring opening of a-aminobutyrolactone, subsequent 1,3-diketone synthesis and heteroannulation via cascade reaction involving debenzylation, intramolecular cyclization and imine reduction under hydrogenation condition are the key steps involved in the synthesis.

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A metal catalyst-free and one-pot synthesis of (3,4- dihydro-2H-benzo[b][1,4]oxazin-2-yl)methanol derivatives in water

A robust and metal catalyst-free method has been developed for the general and green synthesis of racemic (3,4-dihydro-2H-benzo[b][1,4] oxazin-2-yl)methanol derivatives. This simple, mild and practical method involves the reaction of 2-aminophenols with ()-epichlorohydrin in the presence of NaOH in water at room temperature. The reaction features high regioselectivity and a good substrate scope to produce both N-substituted and N-unsubstituted products.

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Diversity oriented concise asymmetric synthesis of azasugars: a facile access to L-2,3-trans-3,4-cis-dihydroxyproline and (3S,5S)-3,4,5-trihydroxypiperidine

Diversity oriented concise asymmetric syntheses of L-2,3-trans-3,4-cis-dihydroxyproline and (3S,5S)- 3,4,5-trihydroxypiperidine have been developed from (R)-glycidol. The key step of the synthesis is Sharpless asymmetric dihydroxylation on enantiomerically pure TBDMS protected allylic alcohol 14 which generates the triol intermediate 15 in excellent de. The (2R,3R,4S)-2,3-dihydroxypentanoate derivative 15 was subsequently converted to natural pyrrolidine azasugar 1 and non-natural piperidine azasugar 4 under cascade reaction conditions in good yields.

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A greener approach towards double heteroarylation of N, O and S nucleophiles: synthesis of bioactive polynuclear fused Nheteroarenes

A catalyst, ligand and solvent free method for double heteroarylation of N, O and S nucleophiles has been developed for the first time leading towards the synthesis of compounds containing an indole ring fused with pyrrolo-, furo- and thieno[2,3-b]quinoxaline moieties. This general and greener approach afforded novel compounds of medicinal importance.

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2014

Synthesis of tetrahedral diarylheptanoid ent-diospongin A and epimer-diospongin B by employing Julia–Kocienski olefination

Total synthesis of ent-diospongin A and epimer-diospongin B has been accomplished in good yield with high optical purity. The key steps of diospongin synthesis involve Julia–Kocienski olefination, Weinreb amide formation, Grignard reaction, reduction, acetonide deprotection, Lewis acid catalyzed cyclization, and Wacker oxidation.

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Effect of Aqueous Polyethylene Glycol on 1,3-Dipolar Cycloaddition of Benzoylnitromethane/Ethyl 2-Nitroacetate with Dipolarophiles: Green Synthesis of Isoxazoles and Isoxazolines

A 1:1 mixture of water-polyethylene glycol (PEG) facilitated the 1,3-dipolar cycloaddition of benzoylnitromethane/ethyl 2-nitroacetate with terminal alkynes or alkenes leading to isoxazoles or isoxazolines under green conditions. The methodology is free from the use of any base, catalyst, dehydrating agent or hazardous solvent.

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Applications of Gage Reproducibility & Repeatability (GRR): Understanding and Quantifying the Effect of Variations from Different Sources on a Robust Process Development

During process development, it is always a debatable issue whether the variation in analytical results is due to the measurement system (MS) or due to the process. The best approach is to quantify total variation coming from the MS prior to any process improvement activity. This quantification is done by “Gage Reproducibility & Repeatability” (GRR). This article describes the usage of GRR for quantifying variation from various sources and selecting a suitable MS for the analysis. In this study, two instruments, a potentiometer and ultra high pressure liquid chromatography (UPLC), were evaluated for the assay measurement of a key starting material (KSM) supplied by a vendor. As a result of the GRR study, it was found that the potentiometer was not a suitable instrument, because of the high variation contributed by it, whereas UPLC was found to be suitable, because of the insignificant variation contributed by it towards the assay. In addition to this, it was also observed that the variation contributed by the KSM samples was insignificant, indicating that those samples were coming from a robust process, and the vendor was found to be suitable for supplying the KSM.

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Synthesis of tetrahedral diarylheptanoid ent-diospongin A and epimer-diospongin B by employing Julia–Kocienski olefination

Total synthesis of ent-diospongin A and epimer-diospongin B has been accomplished in good yield with high optical purity. The key steps of diospongin synthesis involve Julia–Kocienski olefination, Weinreb amide formation, Grignard reaction, reduction, acetonide deprotection, Lewis acid catalyzed cyclization, and Wacker oxidation.

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An oxidative amidation and heterocyclization approach for the synthesis of β-carbolines and dihydroeudistomin Y

A novel synthetic methodology has been developed for the synthesis of dihydro-β-carboline derivatives employing oxidative amidation–Bischler–Napieralski reaction conditions using tryptamine and 2,2-dibromo-1-phenylethanone as key starting materials. A number of dihydro-β-carboline derivatives have been synthesized in moderate to good yields using this methodology. Attempts were made towards the conversion of these dihydro-β-carbolines to naturally occurring eudistomin alkaloids.

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Reactions of salicylaldehydes with activated terminal alkynes in aqueous media: synthesis of 3- substituted 4-hydroxy chromenes as potential cytotoxic agents

Terminal alkynes containing ester, amide or ketone moieties have been reacted with salicylaldehydes in the presence of DABCO affording a direct and single-step method for the regioselective synthesis of 3-substituted 4-hydroxy-4H-chromenes in aqueous 1,4- dioxane. A number of novel chromene derivatives were prepared in good yields using this methodology some of which showed cytotoxic properties when tested against cancer cells.

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A simple access to N-(un)substituted isoquinolin1(2H)-ones: unusual formation of regioisomeric isoquinolin-1(4H)-ones

A ligand/additive/Pd-free Cu-mediated coupling/cyclization strategy afforded the first practical, one-pot and general approach towards synthesis of N-(un)substituted isoquinolin-1(2H)-ones. Both the catalyst and the solvent used are recyclable. The use of the Cu reagent in excess led to the unusual formation of regioisomeric and uncommon isoquinolin-1(4H)-ones.

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2013

Synthesis of enantiomerically pure N-(2,3-dihydroxypropyl)arylamides via oxidative esterification

A highly efficient synthesis of enantiomerically pure (S) and (R)-isomers of N-(2,3-dihydroxypropyl)arylamides has been developed with good overall yields in a two step process. The key step involves the ring opening of the chiral epoxide with a nitrogen heterocyclic carbene (NHC) and further rearrangement to chiral N-(2,3-dihydroxypropyl)arylamides in high yields and enantioselectivity. During the reaction, no erosion in chiral purity was observed.

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Diastereoselective total synthesis of 3,6-disubstituted piperidine alkaloids, (3R,6S)-epi-pseudoconhydrine and (3R,6R)-pseudoconhydrine

Diastereoselective total synthesis of 3,6-disubstit uted piperidine alkaloids, epi-pseudoc onhydrine (1) and pseudoconhydrine (2) has been developed starting from enantiopure (S)-epichlorohydrin. The key steps in the synthesis of these alkaloi ds involved a-aminobutyrolacton e ring opening with N,O-dimethyhydroxyl amine followed by a Grignard reaction and cascade debenzylation-reductive aminativ e cyclization under hydrogenation conditions. High de was obtained in the synthesis of epi-pseudoconhydrine (1).

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Cu-catalyzed coupling-cyclization in PEG 400 under ultrasound: a highly selective and greener approach towards isocoumarins

The combination of CuI–K2CO3-PEG 400 facilitated the couplingcyclization of o-iodobenzoic acid with terminal alkynes under ultrasound, affording a greener and practical approach towards 3-substituted isocoumarins with remarkable regioselectivity. This inexpensive and Pd and ligand free methodology gave rise to various isocoumarins of potential pharmacological interest.

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2012

Iodine catalyzed four-component reaction: a straightforward one-pot synthesis of functionalized pyrroles under metal-free conditions

An iodine-catalyzed four-component reaction of 1,3-dicarbonyl compounds, amines, aldehydes and nitroalkanes afforded polysubstituted pyrroles under a metal free condition. Simplicity, low cost and good yields are the key features of this methodology. The mechanism of this four component process is discussed and structural elaboration of one of the compounds synthesized using Suzuki and Sonogashira coupling is presented.

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N-heterocyclic carbene-mediated hydroacylation–Sonogashira/Heck/Suzuki coupling in a single pot: A new cascade reaction

A dually NHC-catalyzed reaction cascade comprising an initial hydroacylation of an activated ketone and subsequent Sonogashira/Heck/Suzuki coupling in the same pot is reported. The reaction mechanism and scope of the methodology is presented.

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Synthesis of Isoquinoline Alkaloids via Oxidative Amidation–Bischler– Napieralski Reaction

A straightforward synthesis of a-keto amides by coupling primary amines with aryl dibromoethanones under oxidative amidation conditions has been developed. The a-keto amides were then subjected to heterocyclodehydration reaction under Bischler– Napieralski conditions followed by aromatization with DBU provided 1-benzoyl isoquinolines in a two-stage process. Utilizing this methodology, isoquinoline alkaloids such as thalmicrinone, papavaraldine, and pulcheotine A were synthesized in excellent yields.

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An Efficient and Practical Synthesis of Aryl and Hetaryl a-Keto Esters

oxidative esterification of 2,2-dibromo-1-(het)arylethanones by sequential treatment with dimethyl sulfoxide and an alkanol. The versatility of the reaction was established by synthesizing a range of a-keto esters by treatment of 2,2- dibromoethanones, derived from aryl or hetaryl ketones, with dimethyl sulfoxide and a cyclic or acyclic primary or secondary alcohol. The mechanism of the reaction was established by means of a detailed study

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Construction of a quinoline ring via a 3-component reaction in water: crystal structure analysis and H-bonding patterns of a 2-aryl quinoline

Montmorillonite K-10 mediated green and one-pot synthesis of 2-substituted quinolines has been accomplished via a 3-component reaction of aniline, aldehydes and ethyl 3,3- diethoxypropionate in the presence of air oxygen in water. The crystal structure analysis and H-bonding patterns of one compound prepared are presented.

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Construction of a six-membered fused N-heterocyclic ring via a new 3-component reaction: synthesis of (pyrazolo)pyrimidines/pyridinesw

A conceptually new three-component reaction was developed to construct a six-membered fused N-heterocyclic ring affording (pyrazolo)pyrimidines/pyridines as potential inhibitors of PDE4. The reaction is catalyzed by triflic acid in acetic acid in the presence of aerial oxygen.

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2011

Transition metal mediated construction of pyrrole ring on 2,3-dihydroquinolin-4(1H)-one: synthesis and pharmacological evaluation of novel tricyclic heteroarenes

A facile two-step method for the construction of fused pyrrole ring leading to 5-substituted 2,3-dihydro-1H-pyrrolo[3,2,1- ij]quinolin-1-ones via C–C followed by intramolecular C–N bond forming reaction is described. In vitro pharmacological evaluation and molecular modelling studies of some of the compounds synthesized are presented.

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A Concise and Cascade Synthesis of Batracylin and Substituted Isoindolo- [1,2-b]quinazolin-12(10H)-ones

A concise, highly convergent, and practical synthesis of the clinical-phase anticancer agent batracylin in a two-stage process in excellent yield is described. The B and C rings of this tetracyclic heterocycle are constructed by cascade cyclization of 5-nitro-2-aminobenzyl alcohol with 2-cyanomethyl benzoate in trifluoroacetic acid in good yield in a single-pot reaction. A plausible mechanism for the cascade reaction is also proposed. As part of these studies, a range of batracylin derivatives with different substituents on the C and D rings are synthesized.

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Yb(OTf)3 catalyzed new cascade reaction: a facile assembly of fused quinazolinones

A one-pot Yb(III)-mediated cascade reaction has been developed leading to small molecules based on a novel structural motif, i.e. quinazolin-4-one moiety fused with an isoquinoline ring, for potential inhibition of TNF-a.

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Synthesis of novel 5-alkyl/aryl/heteroaryl substituted diethyl 3,4-dihydro-2H-pyrrole-4,4-dicarboxylates by aziridine ring expansion of 2-[(aziridin-1-yl)-1-alkyl/ aryl/heteroaryl-methylene]malonic acid diethyl esters

A novel synthetic methodology has been developed for the synthesis of diethyl 5-alkyl/aryl/heteroaryl substituted 3,4-dihydro-2Hpyrrole-4,4-dicarboxylates (also called 2-substituted pyrroline-4,5-dihydro-3,3-dicarboxylic acid diethyl esters) by iodide ion induced ring expansion of 2-[(aziridin-1-yl)-1-alkyl/aryl/heteroaryl-methylene]malonic acid diethyl esters in very good to excellent yields under mild reaction conditions. The electronic and steric impact of the substituents on the kinetics of ring expansion of N-vinyl aziridines to pyrrolines has been studied. Various diversely substituted novel pyrroline derivatives have been synthesized by this methodology and the products can be used as key intermediates in the synthesis of substituted pyrrolines, pyrroles and pyrrolidines.

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2010

A Concise and Convergent Synthesis of Luotonin B and E

A concise and highly convergent practical synthesis of topoisomerase 1 inhibitor luotonin B was developed in a one-pot process in excellent yields. The C and D rings of luotonin B was constructed by cascade cyclizations of 2-cyanoquinoline-3-aldehyde or 2-cyanoquinoline-3-hemiacetal with methylanthranilate under acidic conditions. The luotonin B was then converted into luotonin E by an acid-catalyzed etherification reaction

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2009

A highly effective synthesis of 2-alkynyl-7-azaindoles: Pd/C-mediated alkynylation of heteroaryl halides in water

The reaction of 4-chloro-2-iodo-7-azaindole with terminal alkynes was investigated using 10% Pd/C– PPh3–CuI as a catalyst system in water. This study afforded a new, mild and selective process for the preparation of 2-alkynyl-4-chloro-7-azaindole in good yields via C–C bond forming reaction. The resulting chloro derivative can be functionalized further via another Pd-mediated C–C bond forming reaction with arylboronic acid.

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2008

Revisiting the reaction of b-chloroacroleins with 2-aminophenol: a new observation

The reaction of b-chloroacrolein with 1 equiv of 2-aminophenol in DMF proceeds smoothly to afford 11-hydroxy derivative of chromenoquinoline in good yield. This single pot method allows for a rapid access to a variety of chromenoquinolines or oxepinoquinolines depending on the nature of b-chloroacrolein used. The structures were established by spectroscopic data and further confirmed by X-ray diffraction analysis. A plausible mechanism for this reaction has been proposed. The reaction seemed to proceed via a chloroimine species, whose intermediacy has been established, followed by the construction of the fused quinoline ring.

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2006

Tandem versus single C–C bond forming reaction under palladium–copper catalysis: regioselective synthesis of a-pyrones fused with thiophene

We herein report a highly convenient protocol for rapid construction of a-pyrone fused with thiophene. This includes one-pot and regioselective synthesis of 4,5-disubstituted and 5-substituted thieno[2,3-c]pyran-7-ones, 6,7-disubstituted and 6-substituted thieno[3,2-c]pyran-4-ones. The synthesis of thieno[2,3-c]pyran-7-ones involves palladium mediated cross coupling of 3-iodothiophene-2-carboxylic acid with terminal alkynes in a simple synthetic operation.

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2005

Palladium-mediated synthesis of 5-substituted 4-alkynylthieno[2,3-c]pyran-7-onesq

We describe here, the first palladium-mediated tandem C–C bond forming reaction between 3-iodothiophene-2-carboxylic acid and terminal alkynes to afford the unexpected 5-substituted 4-alkynylthieno[2,3-c]pyran-7-ones in good yields. 2005 Elsevier Ltd. All rights reserved.

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