Increasing the Structural Span of Alkyne Metathesis

A new generation of alkyne metathesis catalysts, which are distinguished by high activity and an exquisite functional group tolerance, allows the scope of this transformation to be extended beyond its traditional range. They accept substrates that were previously found problematic or unreactive, such as propargyl alcohol derivatives, electron-deficient and electron-rich acetylenes of various types, and even terminal alkynes. Moreover, post-metathetic transformations other than semi-reduction increase the structural portfolio, as witnessed by the synthesis of a annulated phenol derivative via ring-closing alkyne metathesis (RCAM) followed by a transannular gold-catalyzed Conia-ene reaction. Further examples encompass a post-metathetic transannular ketone–alkyne cyclization with formation of a trisubstituted furan, a ruthenium-catalyzed redox isomerization, and a Meyer–Schuster rearrangement/oxa-Michael cascade. These reaction modes fueled model studies toward salicylate macrolides, furanocembranolides, and the cytotoxic macrolides acutiphycin and enigmazole A; moreover, they served as the key design elements of concise total syntheses of dehydrocurvularin (27) and the antibiotic agent A26771B (36)

Cross-Metathesis of Terminal Alkynes

Terminal acetylenes are amongst the most problematic substrates for alkyne metathesis because they tend to undergo rapid polymerization on contact with a metal alkylidyne. The molybdenum complex 3 endowed with triphenylsilanolate ligands, however, is capable of inducing surprisingly effective cross-metathesis reactions of terminal alkyl acetylenes with propynyl(trimethyl)silane to give products of type R1–C≡CSiMe . This unconventional way of introducing a silyl substituent onto an alkyne terminus complements the conventional tactics of deprotonation/silylation and excels as an orthogonal way of alkyne protecting group chemistry for substrates bearing base-sensitive functionalities. Moreover, it is shown that even terminal aryl acetylenes can be cross-metathesized with internal alkyne partners. These unprecedented transformations are compatible with various functional groups. The need to suppress acetylene formation, which seems to be a particularly effective catalyst poison, is also discussed

Applications of piezoelectric actuators to precise and fast positioning tasks

Several classes of low-voltage Piezo Actuators have been developed by Cedrat Technologies in order to cover needs for Precise and/or Fast Positioning. This paper discusses of the ability for these Actuators to meet these needs and illustrates it with various applications (mechanisms, dampers, valves) in instrumentation, space, aircraft and automotive industries

Outer-Sphere Reactivity Shift of Secondary Phosphine Oxide-Based Nickel Complexes: From Ethylene Hydrophosphinylation to Oligomerization

International audienceA new dimension for secondary phosphineoxide (SPOs) ligands is described in this article. Demonstratedon original p-allylic nickel structures, these self-assembledcomplexes trigger catalytic hydrophosphinylationreactions. Addition of a Lewis acid B(C6F5)3 switches the reactivitytowards migratory insertion and thus ethylene oligomerizationthrough an unprecedented outer-sphere interactionwith the coordinated SPO ligand. NMR experimentsand X-ray analyses allowed for the observation ofthe formation of zwitterionic active species as well as theirdegradation pathway