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111.
A new system, I2-KI-K2CO3-H2O, selectively oxidized alcohols to aldehydes and ketones under anaerobic condition in water at 90 degrees C with excellent yields. The process is green, mild and inexpensive. 相似文献
112.
Mohit L. Deb Bhaskar Deka Iftakur Rahman Pranjal K. Baruah 《Tetrahedron letters》2018,59(50):4430-4433
Here we report l-proline catalyzed 3-component reaction of indoles, aldehydes and N-substituted anilines in water as solvent at room temperature for the synthesis of 3-(α,α-diarylmethyl)indoles. The reaction is in fact a Michael addition of N-substituted anilines to alkylideneindolenines. The reaction is very clean, high yielding and having broad substrate scope. A tentative mechanism is proposed. 相似文献
113.
Synthesis of Novel Drug‐Like Small Molecules Based on Quinoxaline Containing Amino Substitution at C‐2
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K. Raghavendra Rao Akula Raghunadh Ramamohan Mekala Suresh Babu Meruva K. Ravi Ganesh T. Krishna Dipak Kalita Eppakayala Laxminarayana Manojit Pal 《Journal of heterocyclic chemistry》2016,53(3):901-908
A series of novel “drug‐like” small molecules based on quinoxaline containing amino substitution at C‐2 were synthesized. All these molecules were prepared either via the reaction of 2‐phenyl‐3‐(piperazin‐1‐yl)quinoxaline with acyl bromides or benzyl bromides or various carboxylic acids or via the reaction of 2‐chloro‐3‐phenylquinoxaline with various amines. The structures of these novel compounds were confirmed by spectral analysis. The strategy used is simple and efficient and afforded good yields of quinoxaline derivatives. 相似文献
114.
115.
Subarna Jyoti Kalita Rajarshi Bayan Jutika Devi Sanfaori Brahma Hormi Mecadon Dibakar Chandra Deka 《Tetrahedron letters》2017,58(6):566-569
A new, simple and efficient synthesis of 4-alkyl-5-methyl-1H-pyrazol-3-ols in water by a two-pot four component reaction of ethyl acetoacetate, hydrazine hydrate, aldehyde and ketone in presence K2CO3 as the catalyst is described. Use of water as the reaction medium, operational simplicity, mild reaction conditions, application of a cost-effective, nontoxic and easily available catalyst with auto-tandem catalysis, wide substrate scope, easy workup and purification process make the protocol highly attractive. 相似文献
116.
A Solvent Switch for the Stabilization of Multiple Hemiacetals on an Inorganic Platform: Role of Supramolecular Interactions
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Alok Ch. Kalita Sandeep K. Gupta Prof. Ramaswamy Murugavel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6863-6875
Reaction of Zn(OAc)2 ? 2 H2O with 2,6‐diisopropylphenyl phosphate (dippH2) in the presence of pyridine‐4‐carboxaldehyde (Py‐4‐CHO) in methanol resulted in the isolation of a tetrameric zinc phosphate cluster [Zn(dipp)(Py‐4‐CH(OH)(OMe))]4 ? 4 MeOH ( 1 ) with four hemiacetal moieties stabilized on the double‐4‐ring inorganic cubane cluster. The change of solvent from methanol to acetonitrile leads to the formation of [Zn(dipp)(Py‐4‐CHO)]4 ( 2 ), in which the coordinated Py‐4‐CHO retains its aldehydic form. Dissolution of 1 in CD3CN readily converts it to the aldehydic form and yields 2 . Similarly 2 , which exists in the aldehyde form in CD3CN, readily converts to the hemiacetal form in CD3OD/CH3OH. Compound 1 is an unprecedented example in which four hemiacetals have been stabilized on a single molecule in the solid state retaining its stability in solution as revealed by its 1H NMR spectrum in CD3OD. The solution stability of 1 and 2 has further been confirmed by ESI‐MS studies. To generalize the stabilization of multiple hemiacetals on a single double‐four‐ring platform, pyridine‐2‐carboxaldehyde (Py‐2‐CHO) was used as the auxiliary ligand in the reaction between zinc acetate and dippH2, leading to isolation of [Zn(dipp)(Py‐2‐CH(OH)(OMe))]4 ( 3 ). Understandably, recrystallization of 3 from acetonitrile yields the parent aldehydic form, [Zn(dipp)(Py‐2‐CHO)]4 ( 4 ). Single‐crystal X‐ray diffraction studies reveal that supramolecular bonding, aided by hydrogen‐bonding interactions involving the hemiacetal functionalities (C?OH, C?OMe, and C?H), are responsible for the observed stabilization. The hemiacetal/aldehyde groups in 1 and 2 readily react with p‐toluidine, 2,6‐dimethylaniline, and 4‐bromoaniline to yield the corresponding tetra‐Schiff base ligands, [Zn(dipp)(L)]4 (L=4‐methyl‐N‐(pyridin‐4‐ylmethylidene)aniline ( 5 ), 2,6‐dimethyl‐N‐(pyridin‐4‐ylmethylene)‐aniline ( 6 ), and 4‐bromo‐N‐(pyridin‐4‐ylmethylene)aniline ( 7 )). Isolation of 5 – 7 opens up further possibilities of using 1 and 2 as new supramolecular synthons and ligands. 相似文献
117.
We study the one-dimensional nonlinear Nernst–Planck–Poisson system of partial differential equations with the class of nonlinear boundary conditions which cover the Chang–Jaffé conditions. The system describes certain physical and biological processes, for example ionic diffusion in porous media, electrochemical and biological membranes, as well as electrons and holes transport in semiconductors. The considered boundary conditions allow the physical system to be not only closed but also open. Theorems on existence, uniqueness, and nonnegativity of local weak solutions are proved. The main tool used in the proof of the existence result is the Schauder–Tychonoff fixed point theorem. 相似文献
118.
119.
An alloyed complex of zinc, sulphur and selenium was synthesized in a controlled fashion using 3-mercaptopropionic acid (MPA) surfactant to obtain a new class of biocompatible, highly luminescent imaging probes. These ZnSe(S) alloyed quantum dots (QDs) exhibited a five fold enhancement in photoluminescence over the native ZnSe nanocrystals. The enhancement in photoluminescence was brought about without any post-preparative surface treatments, under ambient conditions. 3-mercaptopropionic acid (MPA) was found to optimally stabilize the ZnSe(S) alloyed system. The incorporation of S2? from MPA after prolonged refluxing time enabled the formation of ZnSe(S) alloyed QDs with low cytotoxicity. The in vitro assays revealed the synergistic enhancement of photoluminescence with enhancement in dispersibility and high biocompatibility for the ZnSe(S) system. The experimental findings give us a novel range of blue-emitting, Zn-based high luminescence QDs for development of nano-probes for bioimaging applications. 相似文献
120.
We recently proposed a transformation‐free higher‐order compact (HOC) scheme for two‐dimensional (2‐D) steady convection–diffusion equations on nonuniform Cartesian grids (Int. J. Numer. Meth. Fluids 2004; 44 :33–53). As the scheme was equipped to handle only constant coefficients for the second‐order derivatives, it could not be extended directly to curvilinear coordinates, where they invariably occur as variables. In this paper, we extend the scheme to cylindrical polar coordinates for the 2‐D convection–diffusion equations and more specifically to the 2‐D incompressible viscous flows governed by the Navier–Stokes (N–S) equations. We first apply the formulation to a problem having analytical solution and demonstrate its fourth‐order spatial accuracy. We then apply it to the flow past an impulsively started circular cylinder problem and finally to the driven polar cavity problem. We present our numerical results and compare them with established numerical and analytical and experimental results whenever available. This new approach is seen to produce excellent comparison in all the cases. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献