Rajender Varma - Academia.edu (original) (raw)

Papers by Rajender Varma

Research paper thumbnail of Solid state regeneration of ketones from oximes on wet silica supported sodium periodate using microwaves

Tetrahedron Letters, 1997

... of Ketones from Oximes on Wet Silica Supported Sodium Periodate Using Microwaves Rajender S. ... more ... of Ketones from Oximes on Wet Silica Supported Sodium Periodate Using Microwaves Rajender S. Varma,* Rajender Dahiya and Rajesh K. Sainl ... 1987, 28, 645; f) Aizpurua, JM; Juaristi, M.; Lecea, B.; Palomo, C. Tetrahedron 1985, 41, 2903; g) Ranu, BC; Sarkar, DCJ Org. ...

Research paper thumbnail of Iodobenzene diacetate on alumina: Rapid oxidation of alcohols to carbonyl compounds in solventless system using microwaves

Tetrahedron Letters, 1997

In an environmentally benign solventless system, alcohols are rapidly oxidized to carbonyl compou... more In an environmentally benign solventless system, alcohols are rapidly oxidized to carbonyl compounds using alumina-supported iodobenzene diacetate (IBD) as an oxidant under microwave irradiation. © 1997 Elsevier Science Ltd.

Research paper thumbnail of Clay catalyzed synthesis of imines and enamines under solvent-free conditions using microwave irradiation

Tetrahedron Letters, 1997

Research paper thumbnail of Solvent-free synthesis of heterocyclic compounds using microwaves

Journal of Heterocyclic Chemistry, 1999

Microwave-enhanced solvent-free synthetic approach is described that features simplicity, manipul... more Microwave-enhanced solvent-free synthetic approach is described that features simplicity, manipulative ease of the operation and conservation of solvents as the main advantages. This eco-friendly approach, which has found application in facile organic functional group transformations, is applied to rapid assembly of heterocyclic compounds. A variety of solid state reactions are described that occur rapidly at ambient pressure under solventless conditions and provide ready access to intermediates such as enamines and α-tosyloxyketones which can be transformed in situ to biologically significant heterocyclic compounds such as isoflav-3-enes, flavones, quinolones, 2-aroylbenzo[b]furans and thiazoles in one-pot operation. Multicomponent reactions under these solvent-free conditions can be adapted for high speed parallel synthesis and are exemplified by assembly of dihydropyrimidine-2(1H)-ones (Biginelli reaction) and imidazo[1,2-a]annulated pyridines, pyrazines and pyrimidines (Ugi reaction) which may have potential in building a library of such compounds.

Research paper thumbnail of Solvent-free organic syntheses using supported reagents and microwave irradiation

Recent developments in microwave-accelerated solventless organic syntheses are summarised. This e... more Recent developments in microwave-accelerated solventless organic syntheses are summarised. This expeditious and solventfree approach involves the exposure of neat reactants to microwave (MW) irradiation in conjunction with the use of supported reagents or catalysts which are primarily of mineral origin. The salient features of these high yield protocols are the enhanced reaction rates, greater selectivity and the experimental ease of manipulation. Among other reagents recently described in the literature on this eco-friendly green approach, the use of recyclable mineral oxides or supported reagents from our laboratory such as Fe(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 4 NO 3 -clay (clayan), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, CrO 3 -alumina, MnO 2 -silica, NaBH 4 -clay, etc. are highlighted in MW-promoted deprotection, condensation,

Research paper thumbnail of Solvent-free accelerated organic syntheses using microwaves

Pure and Applied Chemistry, 2001

A solvent-free approach for organic synthesis is described which involves microwave (MW) exposure... more A solvent-free approach for organic synthesis is described which involves microwave (MW) exposure of neat reactants (undiluted) either in the presence of a catalyst or catalyzed by the surfaces of inexpensive and recyclable mineral supports such as alumina, silica, clay, or "doped" surfaces, namely, Fe(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, MnO 2 -silica, and NaBH 4 -clay. A variety of deprotection, condensation, cyclization, oxidation, and reduction reactions are presented including the efficient one-pot assembly of heterocyclic molecules from in situ generated intermediates such as enamines and α-tosyloxyketones. The application of this solvent-free MW approach to multicomponent reactions is highlighted that can be adapted for high-speed parallel synthesis of the library of dihydropyrimidine-2(1H)-ones and imidazo [1,2-a]annulated pyridines, pyrazines, and pyrimidines.

Research paper thumbnail of Solvent-free organic syntheses

Green Chemistry, 1999

Recent developments in microwave-accelerated solventless organic syntheses are summarised. This e... more Recent developments in microwave-accelerated solventless organic syntheses are summarised. This expeditious and solventfree approach involves the exposure of neat reactants to microwave (MW) irradiation in conjunction with the use of supported reagents or catalysts which are primarily of mineral origin. The salient features of these high yield protocols are the enhanced reaction rates, greater selectivity and the experimental ease of manipulation. Among other reagents recently described in the literature on this eco-friendly green approach, the use of recyclable mineral oxides or supported reagents from our laboratory such as Fe(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 4 NO 3 -clay (clayan), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, CrO 3 -alumina, MnO 2 -silica, NaBH 4 -clay, etc. are highlighted in MW-promoted deprotection, condensation,

Research paper thumbnail of Clay and clay-supported reagents in organic synthesis

Research paper thumbnail of Tetrahaloindate(III)Based Ionic Liquids in the Coupling Reaction of Carbon Dioxide and Epoxides To Generate Cyclic Carbonates: H-Bonding and Mechanistic Studies

Journal of Organic Chemistry, 2005

The microwave reactions of InX3 with [Q]Y produce a series of tetrahaloindate(III)-based ionic li... more The microwave reactions of InX3 with [Q]Y produce a series of tetrahaloindate(III)-based ionic liquids (ILs) with a general formula of [Q][InX3Y] (Q = imidazolium, phosphonium, ammonium, and pyridinium; X = Cl, Br, I; Y = Cl, Br). The reaction of CO2 with a variety of epoxides has been examined in the presence of these ILs wherein tetrahaloindate(III)-based ILs are found to exhibit high catalytic activities and evidence is presented that supports the significant role of H-bonding interactions in the [Q][InX3Y]-catalyzed coupling reactions. The effects of various parameters such as temperature, pressure, and molar ratio of propylene oxide to catalyst have been investigated, and the plausible reaction mechanism based on the 1H and 13C NMR studies is presented for the formation of propylene carbonate.

Research paper thumbnail of Solid state regeneration of ketones from oximes on wet silica supported sodium periodate using microwaves

Tetrahedron Letters, 1997

... of Ketones from Oximes on Wet Silica Supported Sodium Periodate Using Microwaves Rajender S. ... more ... of Ketones from Oximes on Wet Silica Supported Sodium Periodate Using Microwaves Rajender S. Varma,* Rajender Dahiya and Rajesh K. Sainl ... 1987, 28, 645; f) Aizpurua, JM; Juaristi, M.; Lecea, B.; Palomo, C. Tetrahedron 1985, 41, 2903; g) Ranu, BC; Sarkar, DCJ Org. ...

Research paper thumbnail of Iodobenzene diacetate on alumina: Rapid oxidation of alcohols to carbonyl compounds in solventless system using microwaves

Tetrahedron Letters, 1997

In an environmentally benign solventless system, alcohols are rapidly oxidized to carbonyl compou... more In an environmentally benign solventless system, alcohols are rapidly oxidized to carbonyl compounds using alumina-supported iodobenzene diacetate (IBD) as an oxidant under microwave irradiation. © 1997 Elsevier Science Ltd.

Research paper thumbnail of Clay catalyzed synthesis of imines and enamines under solvent-free conditions using microwave irradiation

Tetrahedron Letters, 1997

Research paper thumbnail of Solvent-free synthesis of heterocyclic compounds using microwaves

Journal of Heterocyclic Chemistry, 1999

Microwave-enhanced solvent-free synthetic approach is described that features simplicity, manipul... more Microwave-enhanced solvent-free synthetic approach is described that features simplicity, manipulative ease of the operation and conservation of solvents as the main advantages. This eco-friendly approach, which has found application in facile organic functional group transformations, is applied to rapid assembly of heterocyclic compounds. A variety of solid state reactions are described that occur rapidly at ambient pressure under solventless conditions and provide ready access to intermediates such as enamines and α-tosyloxyketones which can be transformed in situ to biologically significant heterocyclic compounds such as isoflav-3-enes, flavones, quinolones, 2-aroylbenzo[b]furans and thiazoles in one-pot operation. Multicomponent reactions under these solvent-free conditions can be adapted for high speed parallel synthesis and are exemplified by assembly of dihydropyrimidine-2(1H)-ones (Biginelli reaction) and imidazo[1,2-a]annulated pyridines, pyrazines and pyrimidines (Ugi reaction) which may have potential in building a library of such compounds.

Research paper thumbnail of Solvent-free organic syntheses using supported reagents and microwave irradiation

Recent developments in microwave-accelerated solventless organic syntheses are summarised. This e... more Recent developments in microwave-accelerated solventless organic syntheses are summarised. This expeditious and solventfree approach involves the exposure of neat reactants to microwave (MW) irradiation in conjunction with the use of supported reagents or catalysts which are primarily of mineral origin. The salient features of these high yield protocols are the enhanced reaction rates, greater selectivity and the experimental ease of manipulation. Among other reagents recently described in the literature on this eco-friendly green approach, the use of recyclable mineral oxides or supported reagents from our laboratory such as Fe(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 4 NO 3 -clay (clayan), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, CrO 3 -alumina, MnO 2 -silica, NaBH 4 -clay, etc. are highlighted in MW-promoted deprotection, condensation,

Research paper thumbnail of Solvent-free accelerated organic syntheses using microwaves

Pure and Applied Chemistry, 2001

A solvent-free approach for organic synthesis is described which involves microwave (MW) exposure... more A solvent-free approach for organic synthesis is described which involves microwave (MW) exposure of neat reactants (undiluted) either in the presence of a catalyst or catalyzed by the surfaces of inexpensive and recyclable mineral supports such as alumina, silica, clay, or "doped" surfaces, namely, Fe(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, MnO 2 -silica, and NaBH 4 -clay. A variety of deprotection, condensation, cyclization, oxidation, and reduction reactions are presented including the efficient one-pot assembly of heterocyclic molecules from in situ generated intermediates such as enamines and α-tosyloxyketones. The application of this solvent-free MW approach to multicomponent reactions is highlighted that can be adapted for high-speed parallel synthesis of the library of dihydropyrimidine-2(1H)-ones and imidazo [1,2-a]annulated pyridines, pyrazines, and pyrimidines.

Research paper thumbnail of Solvent-free organic syntheses

Green Chemistry, 1999

Recent developments in microwave-accelerated solventless organic syntheses are summarised. This e... more Recent developments in microwave-accelerated solventless organic syntheses are summarised. This expeditious and solventfree approach involves the exposure of neat reactants to microwave (MW) irradiation in conjunction with the use of supported reagents or catalysts which are primarily of mineral origin. The salient features of these high yield protocols are the enhanced reaction rates, greater selectivity and the experimental ease of manipulation. Among other reagents recently described in the literature on this eco-friendly green approach, the use of recyclable mineral oxides or supported reagents from our laboratory such as Fe(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 4 NO 3 -clay (clayan), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, CrO 3 -alumina, MnO 2 -silica, NaBH 4 -clay, etc. are highlighted in MW-promoted deprotection, condensation,

Research paper thumbnail of Clay and clay-supported reagents in organic synthesis

Research paper thumbnail of Tetrahaloindate(III)Based Ionic Liquids in the Coupling Reaction of Carbon Dioxide and Epoxides To Generate Cyclic Carbonates: H-Bonding and Mechanistic Studies

Journal of Organic Chemistry, 2005

The microwave reactions of InX3 with [Q]Y produce a series of tetrahaloindate(III)-based ionic li... more The microwave reactions of InX3 with [Q]Y produce a series of tetrahaloindate(III)-based ionic liquids (ILs) with a general formula of [Q][InX3Y] (Q = imidazolium, phosphonium, ammonium, and pyridinium; X = Cl, Br, I; Y = Cl, Br). The reaction of CO2 with a variety of epoxides has been examined in the presence of these ILs wherein tetrahaloindate(III)-based ILs are found to exhibit high catalytic activities and evidence is presented that supports the significant role of H-bonding interactions in the [Q][InX3Y]-catalyzed coupling reactions. The effects of various parameters such as temperature, pressure, and molar ratio of propylene oxide to catalyst have been investigated, and the plausible reaction mechanism based on the 1H and 13C NMR studies is presented for the formation of propylene carbonate.