Showing papers by "Srivari Chandrasekhar published in 2004"
TL;DR: In this article, a l-proline catalyzed direct aldol reaction between various aldehydes and acetone was achieved using PEG as the solvent with comparable enantioselectivities and yields to those obtained in other solvents.
76 citations
TL;DR: PEG has been used as a rapid and recyclable reaction medium for the Baylis-Hillman reaction with the conventional basic catalyst DABCO with very good yields of products as mentioned in this paper.
65 citations
TL;DR: Lindlar's catalyst (Pd/CaCO 3 ) in PEG (400) has been found to be the most reusable reaction medium for selective reduction of alkynes to cis-olefins as discussed by the authors.
63 citations
TL;DR: In this paper, electrophilic alkenes bearing an ionic liquid-type appendage have been prepared and used in Diels-Alder cycloadditions, 1,4additions, Heck couplings and Stetter reactions; this new type of support allows easy monitoring of the reactions by NMR and MS as well as simple and efficient work-up and isolation procedures.
57 citations
TL;DR: Oligomers of a new class of sugar amino acids (SAA) using a xylofuranoic acid has been shown to generate a robust 14-helix, which is unprecedented in a cis-SAA.
Abstract: Oligomers of a new class of sugar amino acids (SAA) using a xylofuranoic acid has been shown to generate a robust 14-helix. The design involved the use of xylofuranose with a cis arrangement between the amine and carboxyl groups to promote the adoption of a 14-helix instead of a mixed 12/10-helix observed in a sugar oligomer using a ribofuranoic acid and β-Ala. The observation of a stable right-handed 14-helix in a cis-SAA is unprecedented.
57 citations
TL;DR: L-proline is demonstrated for the first time as a chiral catalyst for transfer aldol reaction between aldehydes and diacetone alcohol.
51 citations
TL;DR: In this article, a facile synthesis of symmetrical and unsymmetrical ethers is achieved by reductive coupling of carbonyl compounds with alkoxysilanes using inert polymethylhydrosiloxane as the hydride source and B(C 6 F 5 ) 3 as the catalytic activator of the PMHS.
48 citations
TL;DR: In this paper, the reaction of tri-O-acetyl-D-glucal with different nitrogen nucleophiles was effectively promoted by a catalytic amount of tris(pentafluorophenyl)borane for the first time in acetonitrile at room temperature to produce a variety of azapseudoglycals via Ferrier rearrangement.
43 citations
TL;DR: In this paper, the Stetter reaction was performed in ionic liquid and the possibility to reuse the solvent has been demonstrated, although it was not possible to recycle the thiazolium catalyst.
Abstract: Imidazolium-type room temperature ionic liquids (RTILs) have been used for the Stetter reaction, affording the desired 1,4-dicarbonyl compounds in good yields. Thiazolium salts and Et3N are efficient catalysts for this reaction performed in ionic liquid. The possibility to recycle and reuse the solvent has been demonstrated, although it was not possible to recycle the thiazolium catalyst. This method was used in the total synthesis of haloperidol.
37 citations
TL;DR: In this article, the first stereoselective total synthesis of (6S)-5,6-dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H-pyran-2-one, a novel α,β-unsaturated-δ-lactone having antifungal activity, isolated from Ravensara crassifolia.
34 citations
TL;DR: In this paper, an attempt to consolidate and critically analyse the research work carried out so far on the processing, properties and application of rice husk silica in various laboratories and also highlighting some results on processing and characterization of RHA and reactive silica obtained from it in the authors' laboratory.
Abstract: Rice husk is an abundantly available waste material in all rice producing countries. In certain regions, it is sometimes used as a fuel for parboiling paddy in the rice mills. The partially burnt rice husk in turn contributes to more environmental pollution. There have been efforts not only to overcome this but also to find value addition to these wastes using them as secondary source of materials. Rice husk contains nearly 20% silica, which is present in hydrated amorphous form. On thermal treatment, the silica converts to crystobalite, which is a crystalline form of silica. However, under controlled burning conditions, amorphous silica with high reactivity, ultra fine size and large surface area is produced. This micro silica can be a source for preparing advanced materials like SiC, Si3N4, elemental Si and Mg2Si. Due to the high pozzolanic activity, this rice husk silica also finds application in high strength concrete as a substitute for silica fume. Possibility of using this silica as filler in polymers is also studied. The present paper is an attempt to consolidate and critically analyse the research work carried out so far on the processing, properties and application of rice husk silica in various laboratories and also highlighting some results on the processing and characterization of RHA and reactive silica obtained from it in the authors' laboratory.
TL;DR: The ionic liquids [bmim][BF4] and [mim][NTf2] are used as efficient recyclable solvents in the ytterbium triflate catalysed carbon-Ferrier rearrangement of triacetyl glucal with allyl silanes, propargyl silane, and silyl enolethers as mentioned in this paper.
Abstract: The ionic liquids [bmim][BF4] and [bmim][NTf2] are used as efficient recyclable solvents in the ytterbium triflate catalysed carbon-Ferrier rearrangement of triacetyl glucal with allyl silanes, propargyl silane, and silyl enolethers.
TL;DR: Pd/C in PEG (400) has been found to be an efficient -reusable reaction medium for hydrogenation and hydrogenolysis and both the catalyst and PEG were recycled efficiently over four runs without appreciable loss of activity.
Abstract: Pd/C in PEG (400) has been found to be an efficient -reusable reaction medium for hydrogenation and hydrogenolysis. Both the catalyst and PEG were recycled efficiently over four runs without appreciable loss of activity.
TL;DR: A straight forward entry into nine membered B ring of eleutherobin as oxy analog and its cyctotoxic properties on HBL cell lines is described.
TL;DR: Tantalum (V) chloride adsorbed on silicagel has been utilized as an efficient catalyst for ring opening of aziridines with aromatic amines for the synthesis of 1,2-diamines.
TL;DR: In this article, a practical and safe reduction methodology for the conversion of isoxazolines to 1,3-aminols is developed using polymethylhydrosiloxane-Pd(OH) 2 /C.
Abstract: A practical and safe reduction methodology for the conversion of
Δ 2 -isoxazolines to 1,3-aminols is developed using
polymethylhydrosiloxane-Pd(OH) 2 /C. In presence of (Boc) 2 O, the isoxazoline
was converted into N-Boc protected 1,3-aminol in a one-pot procedure.
TL;DR: Lindlar's catalyst (Pd/CaCO 3 ) in PEG (400) has been found to be the most reusable reaction medium for selective reduction of alkynes to cis-olefins as mentioned in this paper.
Abstract: Lindlar's catalyst (Pd/CaCO 3 ) in PEG (400) has been found to be the most reusable reaction medium for selective reduction of alkynes to cis-olefins. The catalyst and PEG were recycled five times without loss of activity.
Journal Article•
TL;DR: In the case of II and III ox idation states, metal-metal bonds are rather routinely fused as discussed by the authors, however they can complex well in a ll the oxidation states viz., II, III, IV and V.
Abstract: Nb and Ta have very little cationic behaviour, however they can complex well in a ll the oxidation states viz., II , III , IV and V. In the case of II and III ox idation states, metal-metal bonds are rather routinely fo rmed. With reference to abundance, Nb is 1012 times more abundant in the earth crust than Ta. The main source being co lumbitetantalite series o f minerals hav ing general che mical composItIon (Fe/Mn) (NblTah0 6 with va rying ratios. Both metals are bright, high melting (Nb 2468 DC, Ta 2996 DC) and ve ry res istant to acids.
TL;DR: In this article, electrophilic alkenes bearing an ionic liquid-type appendage have been prepared and used in Diels-Alder cycloadditions, 1,4additions, Heck couplings and Stetter reactions; this new type of support allows easy monitoring of the reactions by NMR and MS as well as simple and efficient work-up and isolation procedures.
Abstract: Novel electrophilic alkenes bearing an ionic liquid-type appendage have been prepared and used in Diels–Alder cycloadditions, 1,4-additions, Heck couplings and Stetter reactions; this new type of support allows easy monitoring of the reactions by NMR and MS as well as simple and efficient work-up and isolation procedures.
TL;DR: In this paper, a l-proline catalyzed direct aldol reaction between various aldehydes and acetone was achieved using PEG as the solvent with comparable enantioselectivities and yields to those obtained in other solvents.
Abstract: A rapid l -proline catalyzed direct aldol reaction between various aldehydes and acetone was achieved using PEG as the solvent with comparable enantioselectivities and yields to those obtained in other solvents. Recycling the catalyst and solvent (PEG) was possible 10 times without loss of activity.
TL;DR: PEG has been used as a rapid and recyclable reaction medium for the Baylis-Hillman reaction with the conventional basic catalyst DABCO with very good yields of products as mentioned in this paper.
Abstract: PEG (400) has been used as a rapid and recyclable reaction medium for the Baylis–Hillman reaction with the conventional basic catalyst DABCO (20 mol %) with very good yields of products. Recyclability is achieved with no further addition of DABCO to the reaction medium for over four runs without substantial loss in yields. Incidentally, DABCO is recycled for the first time in this transformation.
TL;DR: In this article, a facile synthesis of symmetrical and unsymmetrical ethers is achieved by reductive coupling of carbonyl compounds with alkoxysilanes using inert polymethylhydrosiloxane as the hydride source and B(C 6 F 5 ) 3 as the catalytic activator of the PMHS.
Abstract: A facile synthesis of symmetrical and unsymmetrical ethers is achieved by reductive coupling of carbonyl compounds with alkoxysilanes. This reaction is performed using inert polymethylhydrosiloxane as the hydride source and B(C 6 F 5 ) 3 as the catalytic activator of the PMHS.
TL;DR: In the case of II and III ox idation states, metal-metal bonds are rather routinely fused as mentioned in this paper, however they can complex well in a ll the oxidation states viz., II, III, IV and V.
Abstract: Nb and Ta have very little cationic behaviour, however they can complex well in a ll the oxidation states viz., II , III , IV and V. In the case of II and III ox idation states, metal-metal bonds are rather routinely fo rmed. With reference to abundance, Nb is 1012 times more abundant in the earth crust than Ta. The main source being co lumbitetantalite series o f minerals hav ing general che mical composItIon (Fe/Mn) (NblTah0 6 with va rying ratios. Both metals are bright, high melting (Nb 2468 DC, Ta 2996 DC) and ve ry res istant to acids.
TL;DR: In this article, a practical and safe reduction methodology for the conversion of isoxazolines to 1,3-aminols is developed using polymethylhydrosiloxane-Pd(OH) 2 /C.
Abstract: A practical and safe reduction methodology for the conversion of
Δ 2 -isoxazolines to 1,3-aminols is developed using
polymethylhydrosiloxane-Pd(OH) 2 /C. In presence of (Boc) 2 O, the isoxazoline
was converted into N-Boc protected 1,3-aminol in a one-pot procedure.
TL;DR: Pd/C in PEG (400) has been found to be an efficient -reusable reaction medium for hydrogenation and hydrogenolysis as mentioned in this paper, and both the catalyst and PEG were recycled efficiently over four runs without appreciable loss of activity.
Abstract: Pd/C in PEG (400) has been found to be an efficient -reusable reaction medium for hydrogenation and hydrogenolysis. Both the catalyst and PEG were recycled efficiently over four runs without appreciable loss of activity.
TL;DR: In this article, the reaction of tri-O-acetyl-D-glucal with different nitrogen nucleophiles was effectively promoted by a catalytic amount of tris(pentafluorophenyl)borane for the first time in acetonitrile at room temperature to produce a variety of azapseudoglycals via Ferrier rearrangement.
Abstract: The reaction of tri-O-acetyl-D-glucal with different nitrogen nucleophiles was effectively promoted by a catalytic amount of tris(pentafluorophenyl)borane for the first time in acetonitrile at room temperature to produce a variety of azapseudoglycals via Ferrier rearrangement in good yields and preferential anomeric selectivity.