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Pintu K. Kundu 《Tetrahedron》2010,66(44):8562-8568
The β-aryl-β-silyl and β,β-disilyl propionates have been synthesized from cinnamates and β-silyl acrylates by a regiospecific reductive C-silylation using Mg/silyl chloride/DMF system at room temperature. These reductive C-silylation conditions have also been applied to δ-aryl substituted dienoates wherein silylation took place at the δ-position leading to the synthesis of single regioisomeric allylsilanes with very high stereoselectivity. 相似文献
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Palladium catalyzed intramolecular aminoacetoxylation of d-ribose derived alkenyl tosylsulfonamide to deliver l-deoxyallonojirimycin in an overall yield of 19%. The preliminary screening of l-deoxyallonojirimycin against carbohydrate processing enzymes showed moderate inhibitory activity against α-glucosidase (yeast) and α-mannosidases. 相似文献
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An efficient synthetic strategy has been developed for the synthesis of the tri, tetrasaccharide block and pentasaccharide corresponding to the capsular polysaccharide of Streptococcus pneumonia serotype 18C as their 2-aminoethyl glycosides. A one-pot glycosylation-deprotection, sequential glycosylations strategy has been adopted for the construction of the fragments and pentasaccharide derivative, which were then transformed into target compound after a series of functional group transformations. The synthetic method relies on the use of p-methoxybenzyl ether as an in situ-removable protecting group to reduce the number of reaction steps significantly. Here H2SO4-silica has been used successfully as a promoter for all glycosylation reaction. In addition, the synthetic target also contained a free amino group at its reducing end, facilitating its conjugation with other molecules for various biological studies and applications. 相似文献
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A. Talapatra S.K. Das S.K. Bandyopadhyay P. Barat Pintu Sen R. Rawat A. Banerjee T. Butz 《Journal of Physics and Chemistry of Solids》2009,70(3-4):527-532
Measurements of the critical current density (Jc) by magnetisation and the upper critical field (Hc2) by magnetoresistance have been performed for hafnium-doped MgB2. There has been a remarkable enhancement of Jc as compared to that by ion irradiation without any appreciable decrease in Tc, which is beneficial from the point of view of applications. The irreversibility line extracted from Jc shows an upward shift. In addition, there has been an increase in the upper critical field which indicates that Hf partially substitutes for Mg. Hyperfine interaction parameters obtained from time differential perturbed angular correlation (TDPAC) measurements revealed the formation of HfB and HfB2 phases along with the substitution of Hf. A possible explanation is given for the role of these species in the enhancement of Jc in MgB2 superconductor. 相似文献
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Fascione MA Adshead SJ Mandal PK Kilner CA Leach AG Turnbull WB 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(10):2987-2997
Sulfoxides are frequently used in organic synthesis as chiral auxiliaries and reagents to mediate a wide variety of chemical transformations. For example, diphenyl sulfoxide and triflic anhydride can be used to activate a wide range of glycosyl donors including hemiacetals, glycals and thioglycosides. In this way, an alcohol, enol or sulfide is converted into a good leaving group for subsequent reaction with an acceptor alcohol. However, reaction of diphenyl sulfoxide and triflic anhydride with oxathiane-based thioglycosides, and other oxathianes, leads to a different process in which the thioglycoside is oxidised to a sulfoxide. This unexpected oxidation reaction is very stereoselective and proceeds under anhydrous conditions in which the diphenyl sulfoxide acts both as oxidant and as the source of the oxygen atom. Isotopic labelling experiments support a reaction mechanism that involves the formation of oxodisulfonium (S-O-S) dication intermediates. These intermediates undergo oxygen-exchange reactions with other sulfoxides and also allow interconversion of axial and equatorial sulfoxides in oxathiane rings. The reversibility of the oxygen-exchange reaction suggests that the stereochemical outcome of the oxidation reaction may be under thermodynamic control, which potentially presents a novel strategy for the stereoselective synthesis of sulfoxides. 相似文献
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Bipul Das K. Mandal Pintu Sen Ashish Bakshi Pradip Das 《Physica B: Condensed Matter》2012,407(18):3767-3773
Room temperature magnetization of two dimensional (2D) arrays of cobalt nanowires (NWs) having diameter 50 and 150 nm prepared by electrodeposition are studied in details. Diffraction patterns of the NWs reveal that the crystallites of the NWs become more textured on decreasing their diameter. Magnetic hysteresis loop measurements show the magnetic easy axis changes its direction from axial to perpendicular direction of NWs on increasing the length of the NWs. The magnetostatic interaction among the NWs, known as the key factor in defining the easy direction is found not to be dipolar at all the circumstances. An aspect ratio (length/diameter of NWs) dependence of the non-dipolar interaction in 150 nm NWs is evident from the static magnetization as well as from ferromagnetic resonance (FMR) measurements. 相似文献
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Azobenzene Isomerization-Induced Photomodulation of Electronic Properties of N-Heterocyclic Carbenes
Aminul Islam Sk Dr. Kshama Kundu Dr. Pintu K. Kundu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(19):4214-4219
Azobenzene-based protonated N-heterocyclic carbenes (NHCs), N,N’-bis(azobenzene)imidazolium chlorides (IAz-X⋅HCl; X=OMe, Br, H) were successfully synthesized and switching abilities of the attached azobenzene units along with the concomitant photoinduced generation of geometric isomers were studied. Upon irradiation with 365 nm UV light, a p-methoxy-azobenzene derivative get transformed from all-trans isomer to nearly all-cis isomer at the photostationary state. The extent of photomodulation of electronic properties in the NHC ring of the p-methoxy-azobenzene derivative is determined through the Tolman Electronic Parameter (TEP). Iridium complex, [(IAz-OMe)IrCl(CO)2] was synthesized and infrared spectra were recorded in dichloromethane solution as film in NaCl crystals and by drop-casting in an ATR crystal. Comparison in averaged carbonyl stretching frequency between all-trans isomer ( ) and all-cis isomer ( ) indicates a significant decrement of Δtt–cc av=2.7 cm−1 (film) and 3.8 cm−1 (ATR). Therefore, moderate to excellent enhancement of electron density (Δtt–cc TEP=2.3 cm−1 [film] and 3.2 cm−1 [ATR]) at the C-2 position of the NHC is achieved through trans→cis isomerization of the remotely placed azobenzene units. This fine phototuning of electron-donating ability at the catalytic center would pave the way to control NHC/NHC-metal catalyzed organic transformations through external stimuli. 相似文献
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160 MeV of neon ion irradiation has been carried out on MgB2 polycrystalline pellets at various doses. There has not been any significant change in Tc except at the highest dose of 1×1015 ions/cm2. Increase in resistivity has been noticed. Resistivity data have been fitted with Bloch-Grüneisen function to extract the values of Debye temperature, residual resistivity and temperature coefficient of resistivity for irradiated as well as unirradiated samples. There has not been any significant effect on electron-phonon coupling due to irradiation as evident from Debye temperature and the electron-phonon coupling constant. 相似文献
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Triptesh Kumar Roy Ramdas Sreedharan Pintu Ghosh Dr. Thirumanavelan Gandhi Prof. Debabrata Maiti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(21):e202103949
Biocatalysis integrate microbiologists, enzymologists, and organic chemists to access the repertoire of pharmaceutical and agrochemicals with high chemoselectivity, regioselectivity, and enantioselectivity. The saturation of carbon-carbon double bonds by biocatalysts challenges the conventional chemical methodology as it bypasses the use of precious metals (in combination with chiral ligands and molecular hydrogen) or organocatalysts. In this line, Ene-reductases (ERs) from the Old Yellow Enzymes (OYEs) family are found to be a prominent asymmetric biocatalyst that is increasingly used in academia and industries towards unparalleled stereoselective trans-hydrogenations of activated C=C bonds. ERs gained prominence as they were used as individual catalysts, multi-enzyme cascades, and in conjugation with chemical reagents (chemoenzymatic approach). Besides, ERs’ participation in the photoelectrochemical and radical-mediated process helps to unlock many scopes outside traditional biocatalysis. These up-and-coming methodologies entice the enzymologists and chemists to explore, expand and harness the chemistries displayed by ERs for industrial settings. Herein, we reviewed the last five year's exploration of organic transformations using ERs. 相似文献