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Ruthenium phosphido complexes have been shown to be excellent nucleophiles, reacting via two-electron processes with a variety of electrophiles. A catalytic alkylation reaction was developed using an achiral ruthenium complex, which was then elaborated into a catalytic enantioselective synthesis of P-stereogenic phosphines. These useful and synthetically challenging phosphines can now be accessed in a single step from simple secondary phosphines and alkyl halides. Optimization and scope of the enantioselective alkylation are discussed.
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Using a simple analytical model, this paper addresses the following question: Should the Internet retain its best-effort-only architecture, or should it adopt one that is reservation-capable? We characterize the differences between reservation-capable and best-effort-only networks in terms of application performance and total welfare. Our analysis does not yield a definitive answer to the question we pose, since it would necessarily depend on unknowable factors such as the future cost of network bandwidth and the nature of the future traffic load. However, our model does reveal some interesting phenomena. First, in some circumstances, the amount of incremental bandwidth needed to make a best-effort-only network perform as well as a reservation capable one diverges as capacity increases. Second, in some circumstances reservation-capable networks retain significant advantages over best-effort-only networks, no matter how cheap bandwidth becomes. Lastly, we find bounds on the maximum performance advantage a reservation-capable network can achieve over best-effort architectures.
No abstract is provided for this article.
We report the iridium-catalyzed borylation of primary and secondary alkyl C-H bonds directed by a Si-H group to form alkylboronate esters site selectively. The reactions occur with high selectivity at primary C-H bonds γ to the hydrosilyl group to form primary alkyl bisboronate esters. In the absence of such primary C-H bonds, the borylation occurs selectively at a secondary C-H bond γ to the hydrosilyl group, and these reactions of secondary C-H bonds occur with high diastereoselectivity. The hydrosilyl-containing alkyl boronate esters formed by this method undergo transformations selectively at the carbon-boron or carbon-silicon bonds of these products under distinct conditions to give the products of amination, oxidation, and arylation.
A biochemical screening procedure was developed to identify mutants of Arabidopsis thaliana in which the polysaccharide composition of the cell wall was altered. Over 5000 ethyl methanesulfonate—mutagenized plants were analyzed by this method, leading to the identification of 38 mutant lines. One complementation group of mutants was completely deficient in L-fucose, a constituent of pectic and hemicellulosic polysaccharides. These mutant plants were dwarfed in growth habit, and their cell walls were considerably more fragile than normal.
