Claudio Gioia

Organocatalytic Asymmetric Diels-Alder Reactions of 3-Vinylindoles

Diels–Alder type reactions are amongst the most useful transformations in organic chemistry for the construction of cyclohexene structures, often containing multiple stereocenters. Catalytic asymmetric variants of these [4+2] cycloadditions have been reported for different diene–dienophile combinations, showing in several instances outstanding synthetic utility. Herein, we present the development of an unprecedented catalytic asymmetric Diels–Alder reaction of 3-vinylindoles 1 with different representative dienophiles 2 (Scheme 1). Our studies were motivated by the stunning

Organocatalytic Asymmetric Formal [3 + 2] Cycloaddition with in Situ-Generated N-Carbamoyl Nitrones

A novel organocatalytic formal [3 + 2] cycloaddition reaction with in situ generation of N-carbamoyl nitrones is presented. For the first time, N-Boc- and N-Cbz-protected isoxazolidines have been directly obtained as single diastereoisomers in generally high yields and enantiomeric excesses using mild reaction conditions and inexpensive, readily available Cinchona alkaloid quaternary ammonium salts as catalysts. Synthetic manipulations of the products provided highly valuable building blocks such as free isoxazolidines, a N-Boc-1,3-aminoalcohol, and a free delta-lactam. This report represents a pioneering work in the use of N-carbamoyl nitrones as electron-poor 1,3-dipoles and glutaconates as new dipolarophiles in asymmetric catalysis.

Sustainable polyesters for powder coating applications from recycled PET, isosorbide and succinic acid

A new method for the synthesis of polyesters that combines the chemical recycling of poly(ethylene terephthalate) (PET) with the use of monomers derived from renewable resources, such as isosorbide and succinic acid, has been developed. A kinetic study has been performed in order to determine the best catalyst for PET depolymerisation with isosorbide and for the subsequent polycondensation of PET oligomers with succinic acid. Using the correct amounts of isosorbide and succinic acid it is possible to obtain polymers which well fit the properties (glass transition temperature and end-group composition) necessary for powder coating applications. The coating produced using this new environmentally friendly approach presents applicative properties similar, and in some cases superior, to those of a commercial coating obtained from non-renewable resources.

A Sustainable Route to a Terephthalic Acid Precursor.

A new synthetic pathway for the production of p-toluic acid has been developed starting from reagents derived from renewable resources. A Diels-Alder reaction between sorbic and acrylic acids is followed by a combined dehydrogenation/ decarboxylation process, providing p-toluic acid in high yields. This route permits to use milder conditions compared to other Diels-Alder approaches reported in the literature, and therefore can contribute to a more sustainable terephthalic acid production.

Advances in the synthesis of bio-based aromatic polyesters: novel copolymers derived from vanillic acid and ε-caprolactone

A new and sustainable pathway for the synthesis of polyesters and copolyesters derived from vanillic acid is suggested. The poor reactivity of the fenolic –OH group of vanillic acid has been overcome by etherification reactions with biobased ethylene carbonate: the full procedure towards poly(ethylene vanillate) (PEV) avoids solvents and purification steps and uses only bio-based reagents. The PEV thus obtained is an example of bio-based PET mimics, characterized by high thermal transitions and a notable level of crystallinity. However, probably due to its low molecular weight, the material is brittle. In order to solve such problems and to exploit the aromatic structure of PEV to enhance the properties of aliphatic polyesters, new copolymers based on PEV and poly-e-caprolactone were prepared. The new materials are characterized by an EV crystalline phase and tunable thermal properties according to the composition.

Powder coatings for indoor applications from renewable resources and recycled polymers

Powder coatings have been prepared using a sustainable polyester synthesized by combining the chemical recycling of polymers, recovered from post-consumer waste streams, with the use of bio-based monomers. The coatings obtained using this environmentally friendly approach have been compared with those based on a traditional polyester synthesized using nonrenewable resources. The results demonstrate that the new eco-friendly resin presents application performances that in some cases are superior compared to those of the commercial, petro-derived coating. This behavior, combined with the sustainable character of the new technology, gives important advantages in comparison to the conventional resins and opens new possibilities in market segments where the current powder coating has limited applications.

Chemical recycling of post-consumer compact discs towards novel polymers for powder coating applications

New processes for the chemical recycling of bisphenol A polycarbonate (PC), directly from post-consumer compact discs, have been developed. The first recycling method is based on the use of molecules that can be derived from renewable resources (isosorbide, ethylene carbonate and succinic acid). A second procedure involves a one-pot reaction of post consumer PC with ethylene carbonate, without complete degradation to low molecular weight products. The final polymers feature properties that make them suitable for powder coating applications.

Tunable Thermosetting Epoxies Based on Fractionated and Well-Characterized Lignins

Here we report the synthesis of thermosetting resins from low molar mass Kraft lignin fractions of high functionality, refined by solvent extraction. Such fractions were fully characterized by 31P NMR, 2D-HSQC NMR, SEC, and DSC in order to obtain a detailed description of the structures. Reactive oxirane moieties were introduced on the lignin backbone under mild reaction conditions and quantified by simple 1H NMR analysis. The modified fractions were chemically cross-linked with a flexible polyether diamine ( Mn ≈ 2000), in order to obtain epoxy thermosets. Epoxies from different lignin fractions, studied by DSC, DMA, tensile tests, and SEM, demonstrated substantial differences in terms of thermo-mechanical properties. For the first time, strong relationships between lignin structures and epoxy properties could be demonstrated. The suggested approach provides unprecedented possibilities to tune network structure and properties of thermosets based on real lignin fractions, rather than model compounds.

A one-pot biomimetic synthesis of selectively functionalized lignins from monomers: a green functionalization platform

Lignin is the most abundant renewable source of phenolic compounds with great application potential in renewable materials, biofuels and platform chemicals. The current technology for producing cellulose-rich fibers co-produces heterogeneous lignin, which includes an untapped source of monomeric phenolics. One such monomer also happens to be the main monomer in soft wood lignin biosynthesis, namely coniferyl alcohol. Herein, we investigate the potential of coniferyl alcohol as a platform monomer for the biomimetic production of tailored functionalized oligolignols with desirable properties for material synthesis. Accordingly, a bifunctional molecule with at least one carboxyl-ended functionality is included with coniferyl alcohol in biomimetic lignin synthesis to, in one pot, produce a functionalized lignin. The functionalization mechanism is a nucleophilic addition reaction to the quinone methide intermediate of lignin polymerization. The solvent system applied was pure water or 50% aqueous acetone. Several bi-functional molecules differing in the second functionality were successfully inserted in the lignin demonstrating the platform component of this work. Detailed characterization was performed by a combination of NMR techniques which include 1H NMR, COSY-90, 31P NMR, 13C NMR, 13C APT, HSQC, HMBC and HSQC TOCSY. Excellent selectivity towards benzylic carbon and a high functionalization degree were noted. The structure of lignin was tailored through the solvent system choice, with 50% aqueous acetone producing a skeletal structure favorable for a high degree of functionalization. Finally, material concepts are demonstrated using classical thiol–ene- and Diels–Alder-chemistries to show the potential for the thermoset and thermoplastic concepts, respectively. The functionalization concept presents unprecedented opportunities for the green production of lignin-based recyclable biomaterials.

A new approach to the synthesis of monomers and polymers incorporating furan/maleimide Diels-Alder adducts

The Diels–Alder reaction between furan and maleimide moieties is a well-known and widely used strategy to build bio-based macromolecular structures with peculiar properties. The furan-maleimide adducts are thermally reversible because they can be broken above about 120°C and recombined at lower temperatures. At the moment only the monomers exhibiting the furan or the maleimide moieties on their extremity are used in order to get linear or cross-linked polymeric structures. The innovative idea described here consists in using a monomer bearing two carboxylic acidic groups on its extremities and a furan-maleimide Diels-Alder adduct within its structure. This monomer can give rise to classical polycondensation reactions leading to polymers. These polymers (which are polyesters in the present case) can be broken at high temperatures in correspondence of the furane-maleimide Diels-Alder adduct leading to segments exhibiting furan or maleimide moieties at their extremities, which at lower temperature recombine ...