A novel resin-encapsulated nickel nanocatalyst has been synthesized by a modified impregnation me... more A novel resin-encapsulated nickel nanocatalyst has been synthesized by a modified impregnation method using nickel acetate tetrahydrate in presence of sodium borohydride as a mild reducing agent. The synthesized nanocatalyst was characterized by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The concentration of nickel nanoparticles encapsulated on resin was determined by inductively coupled plasma-mass spectroscopy (ICP-MS). Further, synthesized resinencapsulated nickel nanocatalyst was found to be stable and efficient in micromolar concentrations, for the selective reduction of functionalized nitroarenes to corresponding amines in good to high yield, under mild reaction conditions. The nanocatalyst shows excellent reusability.
Aldol Reaction of tert-Butyldimethylsilyloxy Allene with Aromatic Aldehydes, a Direct Route to Ac... more Aldol Reaction of tert-Butyldimethylsilyloxy Allene with Aromatic Aldehydes, a Direct Route to Acrolein Aldol Products.-When the aliphatic aldehyde 3-phenylpropanal is used in the reaction with (II), only polymeric materials are obtained. p-Methoxybenzaldehyde (IIId) does not react, even at room temperature.
Addition of RLi to a mixture of quinuclidine N-oxide (1) and (-)-sparteine in toluene at-78°, fol... more Addition of RLi to a mixture of quinuclidine N-oxide (1) and (-)-sparteine in toluene at-78°, followed by quenching with benzaldehyde gives threo (3, 34% ee) and erythro (4, 40% ee) adducts with moderate enantioselectivity. Reaction of RLi with 1 followed by treatment with (-)sparteine prior to electrophile addition affords racemic products while no deprotonation is observed when 1 is treated with a preformed complex of RLi and (-)-sparteine. These results indicate that only a sequential association of 1 with RLi and (-)-sparteine leads to the complex undergoing enantioselective deprotonation.
Reaction of BF3 coordinated N-ethylpyrrolidine with benzophenone, using a preformed complex of s-... more Reaction of BF3 coordinated N-ethylpyrrolidine with benzophenone, using a preformed complex of s-BuLi and (-)-sparteine for lithiation at-78° C, affords enantio-enriched R-product (er 85: 15). With a warm-cool cycle (-78°→ 0°, 2 h,→-78°) prior to electrophile ...
Lithiation of a series of cyclic aralkyl tertiary amines with sec-BuLi in various solvents has be... more Lithiation of a series of cyclic aralkyl tertiary amines with sec-BuLi in various solvents has been studied. There is a subtle sensitivity to steric factors and lithium coordinating solvents/additives have an adverse effect. ortho-Lithiation is observed only in the case of an eight-membered cyclic amine and the ease of benzylic lithiation with respect to nitrogen is in the surprising order c > b ) a, d. These observations are discussed in the context of nitrogen coordination promoted lithiation.
A novel resin-encapsulated nickel nanocatalyst has been synthesized by a modified impregnation me... more A novel resin-encapsulated nickel nanocatalyst has been synthesized by a modified impregnation method using nickel acetate tetrahydrate in presence of sodium borohydride as a mild reducing agent. The synthesized nanocatalyst was characterized by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The concentration of nickel nanoparticles encapsulated on resin was determined by inductively coupled plasma-mass spectroscopy (ICP-MS). Further, synthesized resinencapsulated nickel nanocatalyst was found to be stable and efficient in micromolar concentrations, for the selective reduction of functionalized nitroarenes to corresponding amines in good to high yield, under mild reaction conditions. The nanocatalyst shows excellent reusability.
Aldol Reaction of tert-Butyldimethylsilyloxy Allene with Aromatic Aldehydes, a Direct Route to Ac... more Aldol Reaction of tert-Butyldimethylsilyloxy Allene with Aromatic Aldehydes, a Direct Route to Acrolein Aldol Products.-When the aliphatic aldehyde 3-phenylpropanal is used in the reaction with (II), only polymeric materials are obtained. p-Methoxybenzaldehyde (IIId) does not react, even at room temperature.
Addition of RLi to a mixture of quinuclidine N-oxide (1) and (-)-sparteine in toluene at-78°, fol... more Addition of RLi to a mixture of quinuclidine N-oxide (1) and (-)-sparteine in toluene at-78°, followed by quenching with benzaldehyde gives threo (3, 34% ee) and erythro (4, 40% ee) adducts with moderate enantioselectivity. Reaction of RLi with 1 followed by treatment with (-)sparteine prior to electrophile addition affords racemic products while no deprotonation is observed when 1 is treated with a preformed complex of RLi and (-)-sparteine. These results indicate that only a sequential association of 1 with RLi and (-)-sparteine leads to the complex undergoing enantioselective deprotonation.
Reaction of BF3 coordinated N-ethylpyrrolidine with benzophenone, using a preformed complex of s-... more Reaction of BF3 coordinated N-ethylpyrrolidine with benzophenone, using a preformed complex of s-BuLi and (-)-sparteine for lithiation at-78° C, affords enantio-enriched R-product (er 85: 15). With a warm-cool cycle (-78°→ 0°, 2 h,→-78°) prior to electrophile ...
Lithiation of a series of cyclic aralkyl tertiary amines with sec-BuLi in various solvents has be... more Lithiation of a series of cyclic aralkyl tertiary amines with sec-BuLi in various solvents has been studied. There is a subtle sensitivity to steric factors and lithium coordinating solvents/additives have an adverse effect. ortho-Lithiation is observed only in the case of an eight-membered cyclic amine and the ease of benzylic lithiation with respect to nitrogen is in the surprising order c > b ) a, d. These observations are discussed in the context of nitrogen coordination promoted lithiation.
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