Rajni Khajuria

Active methylenes in the synthesis of a pyrrole motif: an imperative structural unit of pharmaceuticals, natural products and optoelectronic materials

Pyrrole is one of the most important azaheterocycles, due to its wide range of applications in pharmaceuticals and optoelectronic materials, coupled with its utility as an intermediate in natural products. For several decades, realisation of the scope and potential of this heterocyclic system in both the pharmaceutical and materials industries, has sparked new efforts in finding more efficient synthetic methods for the preparation of pyrrole compounds. Inspired by the importance of this system, herein, we report a review on pyrrole based pharmaceuticals, natural products and optoelectronic materials. Synthetic approaches to pyrrole from active methylenes are also reviewed together with novel reports from our laboratory recently (till 2015).

Alum-Catalyzed Domino Synthesis of 12-Substituted-8,9,10,12-tetrahydrobenzoxanthen-11-ones Under Solvent-Free Conditions

Abstract Alum is found to catalyze efficiently the one-pot, three-component condensation of aldehydes, α/β-naphthol, and dimedone to afford various 12-substituted-8,9,10,12-tetrahydrobenzoxanthen-11-ones in excellent yields. The use of alum catalyst and the solvent-free conditions make this method simple, convenient, eco-friendly, and cost-effective. GRAPHICAL ABSTRACT

One-pot, Solvent-free Cascade Michael-reductive Cyclization Reaction for the Synthesis of Ethyl 3,5-disubstituted-1H-pyrrole-2-carboxylates Under Microwave Irradiation

An efficient, one-pot, solvent-free synthesis of ethyl 3,5-disubstituted-1H-pyrrole-2-carboxylate is achieved by a reaction of 1,3-disubstituted propen-2-one and ethylnitroacetate, in presence of diethylamine (Et2NH) and triethyl- phosphite (P(OEt)3) under microwave (MW) irradiation via cascade Michael-reductive cyclization. The mechanistic out- come of the reaction has also been described. This protocol establishes an easy access to disubstituted-1H-pyrrole-2- carboxylates in one pot.

Reaction of 3-(2-nitrophenyl)-1-arylprop-2-en-1-ones with triethylphosphite in microwave revisited: One-pot synthesis of 2-aroylindoles and 2-arylquinolines

ABSTRACT One-pot synthesis of 2-aroylindoles and 2-arylquinolines has been achieved by the reductive cyclization of 3-(2-nitrophenyl)-1-arylprop-2-en-1-ones with triethylphosphite [P(OEt)3] under microwave irradiation. The formation of 2-arylquinolines by this method is unprecedented. GRAPHICAL ABSTRACT

Synthesis and antimicrobial evaluation of novel 3-(arylideneamino)-3a,8a-dihydroxy-1,3,3a,8a-tetrahydroindeno[1,2-d]imidazole-2,8-diones and their 2-thioxo analogues

ABSTRACT The preparation of some novel 3-(arylideneamino)-3a,8a-dihydroxy-1,3,3a,8a-tetrahydroindeno[1,2-d]imidazole-2,8-diones 8(i–xiv) and 3-(arylideneamino)-3a,8a-dihydroxy-2-thioxo-1,3,3a,8a-tetrahydroindeno[1,2-d]imidazol-8(2H)-ones 9(i–xiv) have been reported through one-pot catalyst-free reaction of aldehydes, semicarbazide hydrochloride/thiosemicarbazide with ninhydrin. All the synthesized compounds have been screened for antimicrobial activity and some of them were observed to possess broad spectrum antibacterial potential as well as significant antagonistic potential against fungal pathogens. GRAPHICAL ABSTRACT

Expeditious synthesis of coumarin-pyridone conjugates molecules and their anti-microbial evaluation

An expedient synthesis of coumarin-pyridone conjugate molecules 2a-o is reported via one-pot reaction between (E)-3-(3-arylacryloyl)-2H-chromen-2-ones 1a-o, ethyl 2-nitroacetate and ammonium acetate. The structures of synthesized compounds have been unambiguously confirmed by spectroscopic analyses (NMR, IR and MS). All the compounds were screened for their anti-microbial activities against three Gram-positive bacterial strains, two Gram-negative bacterial strains and four fungal organisms. Compounds 2d, 2i, 2k, 2o exhibited mild anti-bacterial activity and 2d, 2m were found to be moderately active against all the tested fungal organisms. Compound 2k showed good inhibitory potential against the tested yeasts organisms.Graphical AbstractExpedient synthesis of coumarin-pyridone conjugate molecules has been reported via one-pot, three-component reaction between (E)-3-(3-arylacryloyl)-2H-chromen-2-ones, ethyl 2-nitroacetate and ammonium acetate. Anti-microbial activity of these compounds was evaluated and the results indicated that some of the compounds exhibited mild anti-bacterial activity and good inhibitory potential against the tested fungal organisms.

Single Crystal X-ray Study of 6-Phenyl-4-( p -tolyl)pyridin-2(1 H )-one

The title compound 6-phenyl-4-(p-tolyl)pyridin-2(1H)-one was synthesized via one-pot, three component reaction of (E)-1-phenyl-3-(p-tolyl)-2-propen-1-one, ethyl 2-nitroacetate and ammonium acetate in refluxing ethanol, as a shiny green crystalline solid in 83% yield. Its structure was characterized by spectral studies and unambiguously corroborated by X-ray diffraction crystallography. The crystals of title compound are monoclinic, sp. gr. P21/n, a = 11.8346(7) Å, b = 13.4413(9) Å, c = 17.7626(10) Å, β = 99.479(5)°, and Z = 8. All the rings in molecule of the title compound are planar. Hydrogen interactions play significant role in stabilizing the crystal structure and the supramolecular aggregate of molecules is facilitated by strong N–H···O and C–H···O type of hydrogen interactions.

Ferric nitrate nonahydrate as a mild and efficient catalyst for the synthesis of β-enaminones

and pharmaceutical compounds 8 . Moreover, enamine formation is used for the protection of amino acids 9 . Despite of their wide range of synthetic applications and pharmacological activity, the synthesis of β-enaminones has received little attention. The most well-known method for the synthesis of β-enaminones involves the refluxing of β-dicarbonyl compounds with amines in an aromatic solvent with the azeotropic removal of water 10 . Several improved procedures reported for the synthesis of β-enaminones include the reaction of amines and β-dicarbonyl compounds supported on silica with the microwave irradiation 11 , clay K10/ultra-sound 12 , or NaAuCl4 13 . These compounds have also been prepared by direct condensation of primary amines and β-dicarbonyl compounds in water as solvent 14 . Other methodologies involving silver nanoparticles 15 , tungstophosphoric acid 16 , 3-nitrophenylboronic acid 17 , ytterbium triflate 18 , silica chloride 19 , silica ferric hydrogensulfate 20 and dilute hydrochloric acid 21 have also been developed for the enamination of β-dicarbonyl compounds. Synthesis of enaminones has also been achieved by coupling thioamides with α-diazodicarbonyl compounds 22 . However, most of these methods suffer from one or more of the drawbacks like unsatisfactory yields, long reaction times, lack of general applicability, use of expensive catalysts and tedious experimental procedures. Ferric nitrate nonahydrate has been used as an efficient catalyst in organic transformations 23 . In continuation of our ongoing efforts to the usage of various Lewis acids in organic synthesis 24 , ferric nitrate nonahydrate has been explored for the synthesis of β-enaminones as it is non-toxic, easy to handle and low in cost.