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41.
Catalytic Asymmetric Synthesis of Alkynyl Aziridines: Both Enantiomers of cis‐Aziridines from One Enantiomer of the Catalyst
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Dr. Yong Guan Dr. Maria P. López‐Alberca Dr. Zhenjie Lu Dr. Yu Zhang Dr. Aman A. Desai Dr. Aniruddha P. Patwardhan Yijing Dai Prof. Mathew J. Vetticatt Prof. William D. Wulff 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(43):13894-13900
Alkynyl aziridines can be obtained from the catalytic asymmetric aziridination (AZ reaction) of alkynyl imines with diazo compounds in high yields and high asymmetric inductions mediated by a chiral boroxinate or BOROX catalyst. In contrast to the AZ reaction with aryl‐ and alkyl‐substituted imines, alkynyl imines react to give cis‐substituted aziridines with both diazo esters and diazo acetamides. Remarkably, however, the two diazo compounds give different enantiomers of the cis‐aziridine from the same enantiomer of the catalyst. Theoretical considerations of the possible transition states for the enantiogenic step reveal that the switch in enantiomers results from a switch from Si‐face to Re‐face addition to the imine, which in turn is related to a switch from reaction with an E‐imine in the former and a Z‐isomer of the imine in the latter. 相似文献
42.
The search for alternative methods for the production of new materials or fuel from renewable and sustainable biomass feedstocks has gained increasing attention. In this study, Nypa fruticans (nipa palm) fronds from agricultural residues were evaluated to produce pure cellulose by combining prehydrolysis for 1–3 h at 150 °C, sulfur-free soda cooking for 1–1.5 h at 160 °C with 13–25% active alkali (AA), 0.1% soluble anthraquinone (SAQ) catalyst, and three-stage totally chlorine-free (TCF) bleaching, namely oxygen, peroxymonosulfuric acid, and alkaline hydrogen peroxide stages. The optimal conditions were 3 h prehydrolysis and 1.5 h cooking with 20% AA. Soda cooking with SAQ was better than the kraft and soda process without SAQ. The method decreased the kappa number as a residual lignin content index of pulp from 13.4 to 9.9–10.2 and improved the yields by approximately 6%. The TCF bleaching application produced pure cellulose with a brightness of 92.2% ISO, 94.8% α-cellulose, viscosity of 7.9 cP, and 0.2% ash content. These findings show that nipa palm fronds can be used to produce pure cellulose, serving as a dissolving pulp grade for viscose rayon and cellulose derivatives. 相似文献
43.
An efficient and operationally simple strategy for the synthesis of differently C-3 monosubstituted (9) and disubstituted (10) monocyclic β-lactams is described. This involves reaction of β-lactam carbocation equivalents (8) with an active aromatic, aliphatic and heterocyclic substrates in the presence of a Lewis acid. 相似文献
44.
Alharbi F. F. Aman Salma Ahmad Naseeb Ejaz Syeda Rabia Khosa Rabia Yasmin Abid Abdul Ghafoor Manzoor Sumaira Al-Buriahi M. S. Alrowaili Z. A. Farid Hafiz Muhammad Tahir 《Journal of Solid State Electrochemistry》2022,26(5):1251-1258
Journal of Solid State Electrochemistry - Scientists are increasingly interested in improving electroactive technologies for supercapacitor applications, since energy storage devices have improved... 相似文献
45.
Nonlinear Dynamics - In view of their unique shape morphing behaviour, dielectric elastomer-based minimum energy structures (DEMES) have received an increasing attention in the technology of... 相似文献
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47.
Liu F Stephen AG Adamson CS Gousset K Aman MJ Freed EO Fisher RJ Burke TR 《Organic letters》2006,8(22):5165-5168
Replacing the Pro6 in the p6(Gag)-derived 9-mer "P-E-P-T-A-P-P-E-E" with N-substituted glycine (NSG) residues is problematic. However, incorporation of hydrazone amides ("peptoid hydrazones") can be readily achieved in library fashion. Furthermore, reduction of these hydrazones to N-substituted "peptoid hydrazides" affords a facile route to library diversification. This approach is demonstrated by application to Tsg101-binding compounds designed as potential HIV budding antagonists. [reaction: see text] 相似文献
48.
Bakshi MS Kaura A Miller JD Paruchuri VK 《Journal of colloid and interface science》2004,278(2):472-477
The conductivity, kappa, and Krafft temperature, TK, of sodium dodecyl sulfate (SDS) with poly(amidoamine) dendrimers (PAMAM) of 0.0, 0.5, and 1.0 generations (G) have been determined at different surfactant as well as PAMAM concentrations. The critical micelle concentration of SDS increases with the increase in the amount of each generation and the additive effect of 0.5G is maximum. TK of SDS shows a systematic decrease with maximum reduction in the presence of 0.5G. Atomic force microscopy (AFM) captures a layered pattern of 1.0G in the form of nanorods and no AFM images are detected for 1.0G in the presence of SDS. All results demonstrate that SDS has favorable interactions with ester-terminated 0.5G PAMAM rather than amine-terminated 0.0G and 1.0G. 相似文献
49.
4-Aryl-6-methyl-3,4-dihydro-2(1H)-pyrimidinone esters (DHPMs) readily undergo metalation at the C-6 methyl (vinylogous ester) position on treatment with lithium diisopropylamide at -10 degrees C. The resulting anion intermediates can be treated with electrophilic reagents to afford functionalized DHPMs that have been chemically elaborated mainly at the C-6 position. Di- and trianion formation is also possible at both the vinylogous methyl and NH positions when reactions are performed with excess equivalents of the base. 相似文献
50.