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41.
42.
Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions
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Xiaodong Shen Haohua Huo Chuanyong Wang Bo Zhang Dr. Klaus Harms Prof. Dr. Eric Meggers 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9720-9726
Octahedral iridium(III) complexes containing two bidentate cyclometalating 5‐tert‐butyl‐2‐phenylbenzoxazole ( IrO ) or 5‐tert‐butyl‐2‐phenylbenzothiazole ( IrS ) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5–5.0 mol % catalyst loading) for a variety of reactions with α,β‐unsaturated carbonyl compounds, namely Friedel–Crafts alkylations (94–99 % ee), Michael additions with CH‐acidic compounds (81–97 % ee), and a variety of cycloadditions (92–99 % ee with high d.r.). Mechanistic investigations and crystal structures of an iridium‐coordinated substrates and iridium‐coordinated products are consistent with a mechanistic picture in which the α,β‐unsaturated carbonyl compounds are activated by two‐point binding (bidentate coordination) to the chiral Lewis acid. 相似文献
43.
Lingjie Meng Qinglan Guo Minghua Chen Jiandong Jiang Yuhuan Li Jiangong Shi 《中国化学快报》2018,29(8):1257-1260
A glucosidic indole-lignan conjugate with a novel carbon skeleton, named isatindolignanoside A (1), was isolated from an aqueous extract of the Isatis indigotica roots “ban lan gen”. Its structure was determined by comprehensive analysis of spectroscopic data, enzyme hydrolysis, and electronic CD calculations. Compound 1 is active against Coxsackie virus B3 and represents the first example of natural product having a structural feature of conjugation between indole and lignan, and its plausible biosynthetic pathway is postulated. 相似文献
44.
Herein we discovered that a Nile Red-based probe with a cinnamoyl unit was highly selective and sensitive to N2H4. Hydrazinolysis by N2H4 would release a hydroxyl substituted Nile Red and result in remarkable fluorescence quench. Importantly, Cys/Hcy would not interrupt the N2H4 recognition. This is because, for this probe, the combination of the π-π conjugate system can stabilize the ethylene union, which results in the nucleophilic addition of the thiol group of Cys/Hcy becomes non-effective. 相似文献
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M. B. Deshmukh S. D. Jadhav A. R. Mali A. W. Suryawanshi P. V. Anbhule S. S. Jagtap 《合成通讯》2013,43(23):2967-2971
The conjugate addition of organomanganese reagents to α,β‐unsaturated aldehydes and allylic bisacetate in presence of Me3Si‐Cl and tetrakis acetonitrile copper(I) tetrafluroborate is described. 相似文献
47.
An efficient and simple amine‐catatalyzed azide conjugate addition to α,β‐unsaturated aldehydes has been developed. In the presence of a catalytic amount of tertiary amine with a 1:1 mixture of NaN3 and 37% HCl in CH2Cl2, α,β‐unsaturated aldehydes provided β‐azido aldehydes, which could be transformed into 1,3‐amino alcohols. 相似文献
48.
《Journal of carbohydrate chemistry》2013,32(5):317-329
Mannosyl ethanolamine and BSA were conjugated together by their amino groups with various homobifunctional cross‐linker reagents: disuccinimidyl carbonate (DSC), disuccinimidyl glutarate (DSG), disuccinimidyl suberate (DSS), ethylene glycolbis(succinimidylsuccinate) (EGS), 1,5‐difluoro‐2,4‐dinitrobenzene (DFDNB), diethyl squarate (DES), and thiophosgene (TP). The resulting mannose-BSA conjugates were subjected to an enzyme‐linked lectin assay (ELLA)to investigate their affinity to concanvalin A (ConA). With these results, the seven linkers were evaluated on the basis of five criteria, i.e., cost, reactivity, sugar loading, homogeneity, and affinity to ConA. Thus, DSS, DFDNB, and DES seemed to have advantages over the other cross-linking reagents. 相似文献
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Dr. Daniel Müller Prof. Alexandre Alexakis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(45):15226-15239
Alkenylaluminums undergo asymmetric copper‐catalyzed conjugate addition (ACA) to β‐substituted enones allowing the formation of stereogenic all‐carbon quaternary centers. Phosphinamine–copper complexes proved to be particularly active and selective compared with phosphoramidite ligands. After extensive optimization, high enantioselectivities (up to 96 % ee) were obtained for the addition of alkenylalanes to β‐substituted enones. Two strategies for the generation of the requisite alkenylaluminums were explored allowing for the introduction of aryl‐ and alkyl‐substituted alkenyl nucleophiles. Moreover, alkyl‐substituted phosphinamine (SimplePhos) ligands were identified for the first time as highly efficient ligands for the Cu‐catalyzed ACA. 相似文献