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991.
Dhananjay Yadav Gaurav Shukla Monish A. Ansari Abhijeet Srivastava Maya Shankar Singh 《Tetrahedron》2018,74(40):5920-5931
An operationally simple and efficient one-pot method for the synthesis of 1-aroyl (or alkanoyl)-2-thioalkyl-3-aryl (or alkyl)-3H-benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones has been devised by copper-catalyzed cross-coupling of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols in open air for the first time. The key to the success of this transformation is the room temperature oxidation of α-/β-naphthol to 1,2-naphthoquinone as a reactive species, which undergoes formal [3 + 2] annulation with α-oxoketene N,S-acetals/β-ketothioamides via cascade sequence of Michael addition/tautomerization/oxidation/cyclization/aromatization reactions, enabling addition of a pyrrole/thiophene ring onto naphthoquinone moiety. Further, benzo[e]indole-4,5-diones were transformed to pentacyclic fused phenazine derivatives under solvent-free conditions. Based on our experimental outcomes, a tentative mechanistic rationale for this chemoselective protocol is proposed, which is well validated and supported by the control experiments. 相似文献
992.
Manjula Singh Arvind K. Yadav Lal Dhar S. Yadav Rana Krishna Pal Singh 《Tetrahedron letters》2018,59(33):3198-3201
A convenient and straightforward synthesis of 6-sulfonylated phenanthridines via silver-catalyzed sequential radical insertion, cyclization and aromatization of 2-isocyanobiphenyls is reported. The protocol does not require a phenanthridine scaffold as a substrate and presents a highly regioselective synthesis of 6-alkyl/arylsulfonyl phenanthridines. The protocol utilizes readily available and easy to handle sodium sulfinates as sulfonating agents and potassium persulfate as an oxidant to afford good to excellent yields of the desired products in a one-pot operation at room temperature. 相似文献
993.
Gavireddy Chaithanya Kumar Katta Muralikrishna Vavilapalli Satyanarayana Chintakrinda Suresh Kumar Jhillu Singh Yadav 《Tetrahedron letters》2018,59(5):454-456
A synthetic approach toward the phostriecin, an antitumor natural product is described. The key features of the present synthesis are Wittig reaction, synthesis of homoallylic alcohol using Brown’s protocol (alkoxyallylboration) and RCM for the creation of unsaturated lactone moiety of phostriecin. 相似文献
994.
The present work concerns with the investigation of the effect of dispersion of Silica (SiO2) nanoparticles (NPs) in host ferroelectric liquid crystal (FLC) KCFLC10S on the dielectric and electro-optical properties and ultraviolet-visible (UV-VIS) absorption spectra of the pristine and dispersed systems. We have found that the dispersion of SiO2 NPs in the host FLC strongly influences the various properties of dispersed systems. No evidence of aggregates and clumps in the dispersed system has been observed. Due to SiO2 NPs dispersion, a rapid decrease in dielectric permittivity ε’, increase in conductivity σ with frequency, increase in spontaneous polarisation Ps and decrease in switching time with bias voltage have been observed. Based on the absorption spectra, we have also made an attempt to link the electro-optical and dielectric response with the mechanism of FLC–NPs interactions. 相似文献
995.
Mozhgan Navidi Shreya Yadav Andrey V. Struts Michael F. Brown Nasri Nesnas 《Tetrahedron letters》2018,59(51):4521-4524
We report the synthesis of 9-CD3-9-cis-retinal via a six-step procedure from β-ionone. The steps involve an initial deuteration of the methyl ketone of β-ionone followed by two consecutive Horner-Wadsworth-Emmons (HWE) coupling reactions and their corresponding DIBAL reductions. A final oxidation of the allylic alcohol of the retinol leads to the target compound. This deuterium labeled retinoid is an important cofactor for studying protein-retinoid interactions in isorhodopsin. 相似文献
996.
Syntheses of synthetic analogues of pondaplin 1 have been achieved. Final macrolide construction was accomplished using a Keck macrolactonization reaction. 相似文献
997.
Janardan Singh Yadav 《International journal of quantum chemistry》1983,23(4):1441-1450
The glycan moiety of the bacterial peptidoglycan consists of alternatingly β(1 → 4) linked disaccharides of N-acetylglucosamine (NAG) and its 3-O-D lactic derivative, N-acetyl β-D-muramic acid (NAM). PCILO conformational energy calculations have been carried out for NAG–NAM and NAM–NAG disaccharides to see whether or not the glycan strands possess a chitinlike structure as suggested by earlier workers. In agrement with recent experimental findings, the present results also suggest that the chitinlike structure is energetically disallowed. Furthermore, the bulky N-acetyl substituents at C2 positions of the two sugar molecules are found to be relatively less important in stabilizing mutual orientations of the two pyranosyl rings. 相似文献
998.
Horne WS Yadav MK Stout CD Ghadiri MR 《Journal of the American Chemical Society》2004,126(47):15366-15367
In this paper, we present 1,2,3-triazole epsilon2-amino acids incorporated as a dipeptide surrogate at three positions in the sequence of a known alpha-helical coiled coil. Biophysical characterization indicates that the modified peptides retain much of the helical structure of the parent sequence, and that the thermodynamic stability of the coiled coil depends on the position of the incorporation of the epsilon-residue. Crystal structures obtained for each peptide give insight into the chemical behavior and conformational preferences of the non-natural amino acid and show that the triazole ring can participate in the backbone hydrogen bonding of the alpha-helix as well as template an interhelical crossing between chains in the bundle. 相似文献
999.
A novel three-component expeditious synthesis of 3,6-diaryl-5-mercaptoperhydro-2-thioxo-1,3-thiazin-5-ones from 2-methyl-2-phenyl-1,3-oxathiolan-5-one, an aromatic aldehyde and an N-aryldithiocarbamic acid is reported. The synthesis is diastereoselective and involves tandem Knoevenagel, Michael and ring transformation reactions under solvent-free microwave irradiation in a one-pot procedure. 相似文献
1000.
Using crystal field approach a theoretical estimate of the ground-state wavefunctions of vanadyl ion doped in various crystals
have been made using ESR data and is found to bed
xy in our coordinate system with slight admixture of the excited states
,d
xz andd
yz. The hyperfine interaction parameterP and Fermi contact coupling parameterK have also been estimated for these vanadyl-doped crystals. Results agree with similar studies made earlier. 相似文献