A Single Bioinspired Hexameric Nickel Catechol–Alloxazine Catalyst Combines Metal and Radical Mechanisms for Alkene Hydrosilylation

Mechanisms combining organic radicals and metallic intermediates hold strong potential in homogeneous catalysis. Such activation modes require careful optimization of two interconnected processes: one for the generation of radicals and one for their productive integration towards the final product. We report that a bioinspired polymetallic nickel complex can combine ligand- and metal-centered reactivities to perform fast hydrosilylation of alkenes under mild conditions through an unusual dual radical- and metal-based mechanism. This earth-abundant polymetallic complex incorporating a catechol-alloxazine motif as redox-active ligand operates at low catalyst loading (0.25 mol%) and generates silyl radicals and a nickel-hydride intermediate through a hydrogen atom transfer (HAT) step. Evidence of an isomerization sequence enabling terminal hydrosilylation of internal alkenes points towards the involvement of the nickel-hydride species in chain walking. This single catalyst promotes a hybrid pathway by combining synergistically ligand and metal participation in both inner- and outer- sphere processes.     

Bioinspired Divergent Oxidative Cyclization from Strictosidine and Vincoside Derivatives: Second-Generation Total Synthesis of (−)-Cymoside and Access to an Original Hexacyclic-Fused Furo[3,2-b]indoline

The second-generation synthesis of (−)-cymoside as well as the formation of a new hexacyclic-fused furo[3,2-b]indoline framework is reported. After a Pictet–Spengler condensation between secologanin tetraacetate and tryptamine, the course of the cyclization of the 7-hydroxyindolenine intermediate, generated by oxidation with an oxaziridine, depended on the stereochemistry of the 3-position. The 3-(S)-strictosidine stereochemistry delivered efficiently the scaffold of cymoside via intramolecular coupling with the C16–C17 enol ether, while the 3-(R)-vincoside stereochemistry directed towards the reaction with the C18–C19 terminal alkene and the formation of the unexpected caged compound.     

SUMS: synchronous undulator–monochromator scans at Synchrotron Soleil

A strategy for performing synchronous undulator–monochromator scans (SUMS) compatible with the control system of Synchrotron Soleil has been developed. The implementation of the acquisition scheme has required the development of an electronic interface between the undulator and the beamline. The characterization of delays and jitters in the synchronous movement of various motor axes has motivated the development of a new electronic synchronization scheme among various axes, including the case when one of the axes is electronically accessible in `read‐only' mode. A software prototype has been developed to allow the existing hard continuous software to work in user units. The complete strategy has been implemented and successfully tested at the TEMPO beamline.     

Copper-Catalyzed Carbonylative Cross-Coupling of Alkyl Iodides and Amines

A general copper-catalyzed carbonylative cross-coupling between amines and alkyl iodides is reported. Using a simple combination of catalytic amounts of copper(I) chloride and N,N,N’,N”,N”-pentamethyldiethylenetriamine in the presence of sodium hydroxide under carbon monoxide pressure, a broad range of alkyl iodides and amines can be efficiently coupled to the corresponding amides that are obtained in good to excellent yields. Notable features of this process – the first one relying on a base metal catalyst – include the availability and low cost of the catalytic system, its successful use with primary, secondary, tertiary alkyl iodides and all classes of amines – with no or limited competing nucleophilic substitution without CO incorporation – as well as its efficiency with complex alkyl iodides and amines. Mechanistic studies demonstrated that a radical pathway is operative and the key role of CO.     

Photo-Oxidizing Ruthenium(II) Complexes with Enhanced Visible-Light Absorption and G-quadruplex DNA Binding Abilities

Photosensitizers that gather high photo-oxidizing power and strong visible-light absorption are of great interest in the development of new photo-chemotherapeutics. Indeed, such compounds constitute attractive candidates for the design of type I photosensitizers that are not dependent on the presence of oxygen. In this paper, we report on the synthesis and studies of new ruthenium(II) complexes that display strong visible-light absorption and can oxidize guanine residues under visible-light irradiation, as evidenced by nanosecond transient absorption spectroscopy. The reported compounds also tightly bind to G-quadruplex DNA structures from the human telomeric sequence (TTAGGG repeat). The kinetic and thermodynamic parameters of the interaction of these Ru(II) complexes with G-quadruplex and duplex DNA were studied thanks to luminescence titrations and bio-layer interferometry measurements, which revealed higher affinities towards the non-canonical G-quadruplex architecture. Docking experiments and non-covalent ionic analysis allowed us to gain information on the mode and the strength of the interaction of the compounds towards G-quadruplex and duplex DNA. The different studies emphasize the substantial influence of the position and the number of non-chelating nitrogen atoms on the interaction with both types of DNA secondary structures.     

Résolution du problème de Dirichlet pour lʼéquation du Jacobien prescrit via lʼéquation de Monge–Ampère

We give an alternative proof, based on the Monge–Ampère equation, of Dacorogna and Moser?s result (Dacorogna and Moser, 1990) [4] on the solvability with optimal regularity of the Dirichlet problem for the prescribed Jacobian equation.     

Site‐Selective,Modular Diversification of Polyhalogenated Aryl Fluorosulfates (ArOSO2F) Enabled by an Air‐Stable PdI Dimer

Since 2014, the interest in aryl fluorosulfates (ArOSO₂F) as well as their implementation in powerful applications has continuously grown. In this context, the enabling capability of ArOSO₂F will strongly depend on the substitution pattern of the arene, which ultimately dictates its overall function as drug candidate, material, or bio‐linker. This report showcases the modular, substrate‐independent, and fully predictable, selective functionalization of polysubstituted arenes bearing C?OSO₂F, C?Br, and C?Cl sites, which makes it possible to diversify the arene in the presence of OSO₂F or utilize OSO₂F as a triflate surrogate. Sequential and triply selective arylations and alkylations were realized within minutes at room temperature, using a single and air‐stable Pd^I dimer.     

Synthesis and Molecular Editing of Callyspongiolide,Part 1: The Alkyne Metathesis/trans-Reduction Strategy

A path-scouting investigation into the highly cytotoxic marine macrolide callyspongiolide is reported that capitalizes on the selective formation of the C10−C11 alkene site. While the closure of the macrocycle by ring closing alkyne metathesis (RCAM) with the aid of a molybdenum alkylidyne complex was high yielding, the envisaged semi-reduction of the cycloalkyne to the corresponding E-alkene proved challenging. The reasons are likely steric in origin, in that the methyl branches on either side of the alkyne seem to prevent effective coordination of the substrate to the ruthenium catalyst, which must carry a bulky Cp* ligand to ensure high trans-selectivity. This notion is supported by the preparation of a callyspongiolide analogue, in which the two methyl groups in question are excised; its formation by RCAM followed by trans-hydrostannation/proto-destannation was straightforward. In parallel work the formation of the fully functional building block 54 showed that the presence of an unprotected -OH group allows even hindered substrates to be processed: the protic group adjacent to the triple bond engages with a chloride ligand on the ruthenium catalyst in hydrogen bonding and hence assists in substrate binding. Moreover, the preparation of an alkynylogous callyspongiolide analogue is described.