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951.
952.
Aarón Gutiérrez Collar Dr. Cristina Trujillo Bruce Lockett-Walters Dr. Brendan Twamley Prof. Stephen J. Connon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(30):7275-7279
An anion-binding approach to the problem of preparing enantioenriched γ-lactams from enolisable anhydrides and imines is reported. A simple bisurea catalyst promotes the cycloaddition between α-aryl succinic anhydrides and either PMP- or benzhydryl-protected aldimines to provide γ-lactams with two contiguous stereocentres (one quaternary) with complete diastereocontrol and high to excellent enantioselectivity for the first time. A DFT study has provided insight into the catalyst mode of action and the origins of the observed stereocontrol. 相似文献
953.
Xiangwen Gao Dr. Zarko P. Jovanov Dr. Yuhui Chen Dr. Lee R. Johnson Prof. Peter G. Bruce 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(23):6639-6643
Discharge in the lithium-O2 battery is known to occur either by a solution mechanism, which enables high capacity and rates, or a surface mechanism, which passivates the electrode surface and limits performance. The development of strategies to promote solution-phase discharge in stable electrolyte solutions is a central challenge for development of the lithium-O2 battery. Here we show that the introduction of the protic additive phenol to ethers can promote a solution-phase discharge mechanism. Phenol acts as a phase-transfer catalyst, dissolving the product Li2O2, avoiding electrode passivation and forming large particles of Li2O2 product—vital requirements for high performance. As a result, we demonstrate capacities of over 9 mAh cm−2areal, which is a 35-fold increase in capacity compared to without phenol. We show that the critical requirement is the strength of the conjugate base such that an equilibrium exists between protonation of the base and protonation of Li2O2. 相似文献
954.
Chengli Zu Herbert N. Praay Bruce M. Bell O. David Redwine 《Rapid communications in mass spectrometry : RCM》2010,24(1):120-128
A derivatization procedure has been developed for the improved characterization of fatty alcohol ethoxylate non‐ionic surfactants by liquid chromatography/mass spectrometry. The end hydroxyl group of each surfactant species was converted into an oxycarbonylbenzene‐2‐sulfonic acid group with 2‐sulfobenzoic anhydride under mild conditions. The produced sulfonic acid group allows all species, including fatty alcohols and those with less than three ethoxylates, to be uniformly ionized by electrospray ionization (ESI) mass spectrometry. Both acid and base can be used as a mobile phase additive for liquid chromatography without affecting Mn and average ethoxylate values, although ion intensities are suppressed during the ESI process. The method was used to analyze seven commercial fatty alcohol ethoxylate non‐ionic surfactants, and the determined Mn and EO values were comparable with the results obtained by NMR. The relative ratio of different fatty alcohol based ethoxylates in a sample can also be determined using the summed mass spectral data. Copyright © 2009 The Dow Chemical Company 相似文献
955.
Using certain representations for Eisenstein series, we uniformly derive several Ramanujan-type series for 1/π. 相似文献
956.
Addition reactions of allyl stannanes to an indolo[2′,3′:3,4]pyrido[1,2‐b]isoquinoline imminium salt
Paul C. Unangst Larry D. Bratton David T. Connor Bruce D. Roth J. Ronald Rubin Bharat K. Trivedi 《Journal of heterocyclic chemistry》2000,37(5):1081-1087
The addition of organometallic reagents to the 13b‐position of the indolo[2′,3′:3,4]pyrido[1,2‐b]isoquinoline imminium salt 4 is described. Reaction of 4 with tetraallyl tin in 2‐methoxyethanol gave the allyl adduct 7 in moderate yield. Further elaboration of 7 yielded the pentacyclic benzylidene alcohols 13 and 14 . Structure elucidation of the compounds prepared was achieved by a combination of 1H nmr spec troscopy and X‐ray crystallography. 相似文献
957.
The Orienteering Problem (OP) is an important problem in network optimization in which each city in a network is assigned
a score and a maximum-score path from a designated start city to a designated end city is sought that is shorter than a pre-specified
length limit. The Generalized Orienteering Problem (GOP) is a generalized version of the OP in which each city is assigned
a number of scores for different attributes and the overall function to optimize is a function of these attribute scores.
In this paper, the function used was a non-linear combination of attribute scores, making the problem difficult to solve.
The GOP has a number of applications, largely in the field of routing. We designed a two-parameter iterative algorithm for
the GOP, and computational experiments suggest that this algorithm performs as well as or better than other heuristics for
the GOP in terms of solution quality while running faster. Further computational experiments suggest that our algorithm also
outperforms the leading algorithm for solving the OP in terms of solution quality while maintaining a comparable solution
speed. 相似文献
958.
959.
A method is described for generating stabilized, intensity-limited pulsetrains from a mode-locked Nd:glass laser with internal second-harmonic generation. 相似文献
960.