Catalyst-Free Thia-Michael Addition to α-Trifluoromethylacrylates for 3D Network Synthesis.

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.

Paving the Way towards Sustainability of Polyurethanes: Synthesis and Properties of Terpene-Based Diisocyanate.

Due to growing concerns about environmental issues and the decline of petroleum-based resources, the synthesis of new biobased compounds for the polymer industry has become a prominent and timely topic. P-menthane-1,8-diamine (PMDA) is a readily available compound synthesized from turpentine, a cheap mixture of natural compounds isolated from pine trees. PMDA has been extensively used for its biological activities, but it can also serve as a source of valuable monomers for the polymer industry. In this work, commercial PMDA (ca. 85% pure) was purified by salinization, crystallization, and alkali treatment and then converted into p-menthane-1,8-diisocyanate (PMDI) through a phosgene-free synthesis at room temperature. A thorough analytical study using NMR techniques (1H, 13C, 13C-1H HSQC, 13C-1H HMBC, and 1H-1H NOESY) enables the characterization of the cis-trans isomeric mixtures of both PMDA and PMDI. These structural studies allowed for a better understanding of the spatial configuration of both isomers. Then, the reactivity of PMDI with a primary alcohol (benzyl alcohol) was studied in the presence of nine different catalysts exhibiting different activation modes. Finally, the use of PMDI in the synthesis of polyurethanes was explored to demonstrate that PMDI can be employed as a new biobased alternative to petrochemical-based isocyanates such as isophorone diisocyanate (IPDI).

Understanding the Reshaping of Fluorinated Polyester Vitrimers by Kinetic and DFT Studies of the Transesterification Reaction.

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 ß-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.

Easy Access to Allylic Sulfones Through Transition-Metal-Free Hydrosulfonylation Of Allenes.

A Brønsted acid-mediated addition of (hetero)aryl and (cyclo)alkyl sodium sulfinates to N-allenyl derivatives, which proceeds in water, is described under very smooth conditions. This reaction provided a practical and efficient protocol for the regio- and stereoselective synthesis of allylic sulfones in an atom- and step-economic fashion.

Umpolung Reactivity of in Situ Generated Phosphido-Boranes: An Entry to P-Stereogenic Aminophosphine-Boranes.

The synthesis of P-stereogenic aminophosphine-boranes has been developed on the basis of umpolung reactivity of in situ generated alkylarylphosphido-boranes, which are normally configurationally unstable intermediates. In our case, their high configurational stability was due to the slow release of the hydroxyalkyl protecting group, together with the fast formation of the iodophosphanylborane in the presence of N-iodosuccinimide. The subsequent substitution reaction was found to proceed in moderate to good yields and in a very high stereospecifity (es) using a variety of amines as nucleophiles.

Intramolecular hydrogen bonding in conformationally semi-rigid α-acylmethane derivatives: a theoretical NMR study.

Conformational mobility is a core property of organic compounds, and conformational analysis has become a pervasive tool for synthetic design. In this work, we present experimental and computational (employing Density Functional Theory) evidence for unusual intramolecular hydrogen bonding interactions in a series of α-acylmethane derivatives, as well as a discussion of the consequences thereof for their NMR spectroscopic properties.

Stereospecific Synthesis of α- and ß-Hydroxyalkyl P-Stereogenic Phosphine-Boranes and Functionalized Derivatives: Evidence of the P=O Activation in the BH3 -Mediated Reduction.

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 ß-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.

Synergistic Copper/Enamine Catalysis for the Regio-, Stereo-, and Enantioselective Intermolecular α-Addition of Aldehydes to Allenamides.

We herein describe an intermolecular enantioselective α-addition of aldehydes to allenamides using a dual copper/enamine catalytic system. Highly enantioselective addition of aldehydes was obtained thanks to secondary amine catalysts. The process was found to be highly regio-, stereo-, and enantioselective under mild conditions.

The Hydroxyalkyl Moiety As a Protecting Group for the Stereospecific Alkylation of Masked Secondary Phosphine-Boranes.

The synthesis of functionalized tertiary phosphine-boranes has been developed via a chemodivergent approach from readily accessible (hydroxymethyl) phosphine-boranes under mild conditions. O-Alkylation or decarbonylative P-alkylation product could be exclusively obtained. The P-alkylation reaction was found to proceed in moderate to very good yields and very high enantiospecificity (es >95%) using a variety of alkyl halides as electrophiles. The configurational stability of the sodium phosphido-borane intermediate was also investigated and allowed a deeper understanding of the reaction mechanism, furnishing secondary phosphine-boranes in moderate yield and enantiopurity.

Transition-metal-catalyzed uninterrupted four-step sequence to access trisubstituted isoxazoles.

We 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.

Bifunctional reactivity of Cu(I): sequential ring opening/N-arylation.

The sequential use of a single Cu(I) catalyst enables the one-pot synthesis of N'-arylaminooxazolidinones through a Lewis acid catalyzed rearrangement followed by an N-arylation reaction. Contrary to previous reports, the formation of a cis-fused 5,5-membered ring system occurs during the rearrangement, as proven by X-ray crystallography.