Introducing Chirality at Phosphorus Atoms: An Update on the Recent Synthetic Strategies for the Preparation of Optically Pure P-Stereogenic Molecules

International audienceThe synthesis of phosphorus molecules presenting a chiral center on the P-atom, also known as P-stereogenic compounds, has long attracted the curiosity of the scientific community. Indeed, these chemical compounds feature many peculiar properties, allowing their use in various fields of applications, ranging from medicine to enantioselective catalysis. However, their synthesis, and more particularly the introduction and retention of the chiral information on the phosphorus center, remains a very challenging task. That is why this review article focuses on the recent advances in the enantioselective synthesis of P-stereogenic molecules, with a particular focus on th

The Hydroxyalkyl Moiety As a Protecting Group for theStereospeci c Alkylation of Masked Secondary Phosphine-Boranes

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The Hydroxyalkyl Moiety As a Protecting Group for theStereospeci c Alkylation of Masked Secondary Phosphine-Boranes

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Transition-Metal-Catalyzed Uninterrupted Four-Step Sequence to Access Trisubstituted Isoxazoles

International audienceWe describe herein a novel uninterrupted four-step sequence to access trisubstituted isoxazoles from readily available propargylic alcohols using sequentially iron and palladium catalytic systems. The advantages of such a strategy are illustrated by the high overall yields and the time-saving procedure that are reported

Tunable P‐Stereogenic P,N‐Phosphine Ligands Design: Synthesis and Coordination Chemistry to Palladium

International audienceThe synthesis of P,N heterobidentate phosphine / palladium complexes has been realized from P-stereogenic enantiopure ligands. Five, six or seven membered ring complexes have been fully characterized, notably by X-ray diffraction, allowing the study of the chelation to a "palladium (II) dichloride" unit. The nature of nitrogen coordination site as well as the size of the ring modify the bite-angle at the solid state

Mechanistic aspects of the stereospecific reduction of chiral hydroxyalkyl phosphinates and phosphine oxides

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Mechanistic aspects of the stereospecific reduction of chiral hydroxyalkyl phosphinates and phosphine oxides

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Understanding the reshaping of fluorinated polyester vitrimers by kinetic and DFT studies of the transesterification reaction

International audienceVitrimers are a third class of polymers gathering the mechanical properties and solvent resistance of 3D thermosets and the reprocessability of thermoplastics. This unique behaviour is due to the triggering of certain covalent exchange reactions that allow the network to rearrange upon application of a stimulus. The constitutive feature of vitrimers is the adoption of a glass-like viscosity during the rearrangement of the network, often due to an associative mechanism for the exchange reaction. Transesterification networks are one of the most studied type of vitrimers that usually require the incorporation of a catalyst, implying the associated drawbacks. Our group recently reported catalyst-free transesterification vitrimers in which the ester functions are particularly reactive thanks to the presence of fluorine atoms in a- or b-position. In the present contribution, we present parallel DFT calculations and an experimental kinetic study on model molecules in order to quantitatively assess the effect of neighbouring fluorinated groups on the transesterification reaction rate

Catalyst-Free Epoxy Vitrimers Based on Transesterification Internally Activated by an α–CF 3 Group

International audienceVitrimers are polymer networks in which associative exchange reactions can take place under specific conditions, thus conferring reprocessability to insoluble materials. Recently, catalyst-free vitrimers have emerged as a new generation of vitrimers able to overcome potential leaching, aging, and sintering issues of catalysts and to ensure the preservation of vitrimer properties after numerous reshaping processes. Here, a catalyst-free epoxy vitrimer featuring α-CF3-substituted ester functions is reported. First, a new tetra-acid precursor was synthesized via a catalyst-free thia-Michael addition. A catalyst-free ring-opening polymerization was then performed on two different diepoxy monomers (DGEBA and BDGE) to obtain polymer networks composed of ester linkages. Curing was evaluated by rheology, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) monitoring of the polymerization kinetics. A gel content of over 70% was measured after 24 h in tetrahydrofuran (THF). Finally, the accelerating effect of the α-CF3 group on transesterification reactions was highlighted by stress-relaxation experiments and analyzed computationally on a molecular model system. Reprocessability tests were carried out at 150 °C for 2 h. The mechanical and thermal properties of the reshaped materials were similar to those of the initial ones. This study demonstrates the potential of fluorinated groups as powerful internal activators for transesterification vitrimers

Catalyst-free transesterification vitrimers: activation via α-difluoroesters

International audienceTransesterification vitrimers often require high catalyst loadings to achieve 3D networks reprocessable at moderately high temperature. The addition of an activating group close to the ester bonds allows to synthesize catalyst-free transesterification vitrimers. Here, we unveil the effect of the α-difluoromethylene group as a novel activating group for such materials. Fluorine features exceptional properties, in particular a strong electronegativity enabling CF2 groups to activate the epoxy-acid polymerization, and more interestingly also the transesterification reaction on adjacent esters. Consequently, this fluorinated group affords the easy synthesis of a highly crosslinked reprocessable material that do not require any metallic or organic catalyst. This vitrimer is endowed with advantageous reprocessing abilities and underwent 10 consecutive cycles without loss of mechanical properties. In brief, the vitrimer combines durability, recyclability and is catalyst-free. This discovery is one step further towards recyclable greener polymer