Search

Thia‐Michael additions (1,4‐additions of a thiol to a Michael acceptor) are generally catalyzed by an external Brønsted or Lewis base. A spontaneous (uncatalyzed) Michael addition of thiols to α‐trifluoromethyl acrylates is described, as well as its application to the very efficient preparation of a thermoset. A thorough mechanistic investigation, based on an experimental kinetic study and on DFT calculations, is presented for the addition of arene‐ and alkanethiols to tert‐butyl trifluoromethyl acrylate in polar aprotic solvents, unveiling a probable solvent‐assisted proton transfer in the rate‐determining step and a considerable lowering of the energy barrier induced by the CF3 group. [ABSTRACT FROM AUTHOR]

Vitrimers 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. Following up on a recent report on catalyst‐free transesterification vitrimers in which the ester functions are particularly reactive thanks to the presence of fluorine atoms in α‐ or β‐position, parallel DFT calculations and an experimental kinetic study on model molecules are presented in order to quantitatively assess the effect of neighbouring fluorinated groups on the transesterification reaction rate. [ABSTRACT FROM AUTHOR]

The 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 the introduction of the chiral center on the phosphorus atom. This article summarizes the main synthetic approaches directed towards the enantioselective synthesis of such chemical entities with a historical perspective. Thus, approaches based on the use of chiral auxiliaries attached to the phosphorus atom and the use of chiral stoichiometric reagents will be discussed first, as they were historically the first to be developed. Then, the recent discoveries in the catalytic and enantioselective synthesis and the direct optical resolution of P‐chiral compounds will be discussed. [ABSTRACT FROM AUTHOR]

The 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. Five, six or seven membered ring P,N heterobidentate phosphine / palladium complexes has been synthesized from P‐stereogenic ligands. X‐ray diffraction allowed the effect study of the nature of nitrogen coordination site as well as the size of the ring on the bite‐angle at the solid state. [ABSTRACT FROM AUTHOR]

Access to hydroxy-functionalized P-chiral phosphine-boranes has become an important field in the synthesis of P-stereogenic compounds used as ligands in asymmetric catalysis. A family of optically pure α and β-hydroxyalkyl tertiary phosphine-boranes has been prepared by using a three-step procedure from readily accessible enantiopure adamantylphosphinate, obtained by semi-preparative HPLC on multigram scale. Firstly, a two-step one-pot transformation affords the enantiopure hydroxyalkyl tertiary phosphine oxides in good yields and enantioselectivities. The third step, BH3-mediated reduction, allows the formation of the desired phosphine-boranes with excellent stereospecifity. The mechanistic study of this reduction provides new evidence to elucidate the crucial role of the pendant hydroxy group and the subsequent activation of the PO bond by the boron atom. [ABSTRACT FROM AUTHOR]