177,151 research outputs found
Schlesien in merkantilistischer, geographischer und statistischer Hinsicht / Dargestellt von J. C. Sinapius
No full textVorlageform des Erscheinungsvermerks: Sorau und Leipzig, bei J. W. Ackermann und J. G. Beygan
Nickela‐electrocatalyzed Mild C−H Alkylations at Room Temperature
No full textAbstract Direct alkylations of carboxylic acid derivatives are challenging and particularly nickel catalysis commonly requires high reaction temperatures and strong bases, translating into limited substrate scope. Herein, nickel‐catalyzed C−H alkylations of unactivated 8‐aminoquinoline amides have been realized under exceedingly mild conditions, namely at room temperature, with a mild base and a user‐friendly electrochemical setup. This electrocatalyzed C−H alkylation displays high functional group tolerance and is applicable to both the primary and secondary alkylation. Based on detailed mechanistic studies, a nickel(II/III/I) catalytic manifold has been proposed.Electrochemically enabled nickel‐catalyzed C−H alkylations with primary and secondary alkyl halides have been accomplished under exceedingly mild reaction conditions with Et3N at room temperature. Detailed mechanistic studies provided support for a nickel(II/III/I) manifold. imageDFG http://dx.doi.org/10.13039/501100001659Alexander von Humboldt-Stiftung http://dx.doi.org/10.13039/10000515
The amoebic growth of project costs
No full textIn the public arena, we often hear about projects that have suffered massive cost overruns. Often they are related to large public construction projects such as airports, bridges, or public buildings. Large overruns also exist in private industry. However, often these do not appear in the newspapers, so the public is not as aware of them. Of course, not all projects go badly wrong, but quite a few do, and frequently we find ourselves uncertain of the causes for such overruns. In this paper, industrial projects that overrun and overrun in a surprising manner are considered. In other words, the paper considers those many projects where the extent of the overrun is well beyond what might ever have been anticipated, even though what was going wrong within the projects was, for the most part, understood.The basis for the content of the paper (that is, the structure and lessons), are drawn from a postmortem analysis of many large projects as part of claims analysis, particularly "delay and disruption" claims for projects whose total expenditure appeared, at first look, inexplicable or surprising. The aim of the paper is to contribute to an understanding of how projects go badly wrong, when they do, and in particular to draw some lessons from this exploration that are likely to help all managers. The reasons for cost escalation are not just the responsibility of project managers.<br/
1,4-Iron Migration for Expedient Allene Annulations through Iron-Catalyzed C−H/N−H/C−O/C−H Functionalizations
No full textAbstract C−H activation bears great potential for enabling sustainable molecular syntheses in a step‐ and atom‐economical manner, with major advances having been realized with precious 4d and 5d transition metals. In contrast, we employed earth abundant, nontoxic iron catalysts for versatile allene annulations through a unique C−H/N−H/C−O/C−H functionalization sequence. The powerful iron catalysis occurred under external‐oxidant‐free conditions even at room temperature, while detailed mechanistic studies revealed an unprecedented 1,4‐iron migration regime for facile C−H activations.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659China Scholarship Council https://doi.org/10.13039/50110000454
Understanding the causes and consequences of disruption and delay in complex projects: how system dynamics can help
No full textRemote C–H Functionalizations by Ruthenium Catalysis
No full textAbstract Synthetic transformations of otherwise inert C–H bonds have emerged as a powerful tool for molecular modifications during the last decades, with broad applications towards pharmaceuticals, material sciences, and crop protection. Consistently, a key challenge in C–H activation chemistry is the full control of site-selectivity. In addition to substrate control through steric hindrance or kinetic acidity of C–H bonds, one important approach for the site-selective C–H transformation of arenes is the use of chelation-assistance through directing groups, therefore leading to proximity-induced ortho-C–H metalation. In contrast, more challenging remote C–H activations at the meta- or para-positions continue to be scarce. Within this review, we demonstrate the distinct character of ruthenium catalysis for remote C–H activations until March 2021, highlighting among others late-stage modifications of bio-relevant molecules. Moreover, we discuss important mechanistic insights by experiments and computation, illustrating the key importance of carboxylate-assisted C–H activation with ruthenium(II) complexes. 1 Introduction 2 Stoichiometric Remote C–H Functionalizations 3 meta-C–H Functionalizations 4 para-C–H Functionalizations 5 meta-/ortho-C–H Difunctionalizations 6 Conclusion
Manganese(I)-Catalyzed Substitutive C-H Allylation
No full textThe first manganese(I)-catalyzed C-H allylations with ample scope were achieved by carboxylate assistance. The highly selective C-H/C-O functionalizations proved viable with densely substituted allyl carbonates, and the organometallic C-H allylation strategy set the stage for expedient latestage diversification with excellent levels of positional selectivity
Understanding and Describing London Dispersion Effects in Transition-Metal-Catalyzed C–H Activations
No full textAbstract Transition-metal-catalyzed C–H activation has emerged as a powerful strategy for molecular synthesis with unique levels of resource economy. Weak secondary dispersion interactions were found to play an essential role in these transformations in terms of kinetic efficacy and selectivity. This Account summarizes our group’s recent progress in the rationalization and quantification of London dispersion effects within the transition-metal-catalyzed C–H activation. 1 Introduction 2 Annulation Reactions 3 Alkylation Reactions 4 Arylation Reactions 5 Olefination Reactions 6 Oxygenation Reactions 7 Conclusio
Air-Stable Bifunctional HASPO Preligands for Metal-Catalyzed Cross-Couplings and Direct C-H Bond Arylations
No full textProgress in the use of heteroatom-substituted secondary phosphine oxides (HASPO) as bifunctional preligands in transition-metal-catalyzed cross-coupling reactions as well as C-H bond functionalizations with challenging substrates is summarized herein until July 2010.DF
Nickel‐Catalyzed Electrooxidative C−H Amination: Support for Nickel(IV)
No full textAbstract Nickel‐catalyzed electrochemical C−H aminations were accomplished by chemo‐ and position‐selective C−H activation with ample scope. Detailed mechanistic studies highlighted a facile C−H cleavage with unique chemo‐selectivity, while cyclovoltammetric analysis provided support for a nickel(II/III/IV) manifold.Distinguished International Students Scholarship https://doi.org/10.13039/501100010893Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659Alexander von Humboldt-Stiftung https://doi.org/10.13039/10000515
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