Biomass valorization by C-H activation

Catalytic functionalizations of furfural by selective C-H activations. 

The conversion of biomass derivatives into value-added materials is one of the key branches of the chemical industry of the future. In particular, the C-H functionalization of furan building blocks at the C3, C4 and C5 positions is an important goal in the field of biorefining. This functionalization is an essential condition for improving the inclusion of products from the furan platform in industrial processes. In recent years, the selective formation of new bonds by C-H activation, without changing the redox state of the formyl function, has become an emerging area of JO research. To this end, the use of appropriate furfurylimines, allowing directed C3-H activation of the furan ring, has paved the way for various transformations catalysed by ruthenium or iridium complexes. JO now aims to develop novel strategies for the selective C-H functionalization of the C4 and C5 position. One C4-functionalisation strategy is based on a cooperative palladium/norbornene catalysis, the so-called Catellani reaction. Direct transformations of the C5-H bond into C-X bonds (X = “N”, CF3…), via metal-induced radical processes, will also be studied, which will allow rapid access to complex molecules important in medicinal chemistry and materials science. Finally, in combination with MP expertise, the use of cobalt-based complexes will be considered to make these approaches even more sustainable. For example, well-designed transient steering groups will be attached to the hydroxymethyl substituent of the HMF, and can direct the C-H activation step at the C4 position.

Lignin valorization.

With the support of the ANR (Lidereco) and in collaboration with Prof. Anett Schallmey (TU Braunschweig, DEU), AP (in collaboration with Prof. G. Poli) has initiated a research programme aimed at valorising the products of enzymatic depolymerisation of lignin. Two molecules that can serve as platforms for the synthesis of molecules of interest, guaiacyl- and syringyl-3-hydroxypropanones (GHP and SHP), were identified and synthesised. While the German research team will optimise the enzymatic depolymerisation conditions for the formation and subsequent purification of GHP and SHP, AP is currently developing methods to access indanone-like molecular motifs from these monomers. Other high value-added molecular building blocks such as dihydrochalcones, chromanones and neoflavans can be prepared from GHP and SHP molecules. These molecular platforms could also provide rapid and biobased access to other molecular skeletons such as coumarins encountered in perfumery, benzolactams and tetrahydroisoquinolines, flavonoids and xanthonoids. Applications in synthesis will be envisaged for the preparation of pharmaceutical molecules and natural molecules from bioresources.

Catalytic functionalizations of terpenes. 

AP (in collaboration with Prof. G. Poli) is interested in the activation of terpenes, and in particular limonene, through regioselective C(sp2)-H activation reactions leading to the formation of high value conjugated dienes. An application in the total synthesis of α-bisabolene is under investigation. One of the processes currently being developed is carried out in the presence of a palladium complex and a large amount of silver acetate as oxidant. As a continuation of this project, AP will look at optimising the sustainability of this process by using other methods to reoxidise the Pd(0) formed during the reaction (e.g. electrochemically), which may lead to a possible reduction in the catalytic loading of the introduced palladium salt. The use of other catalysts based on non-noble metals such as cobalt or copper will be considered in the future to replace palladium. Subsequently, other selective C-H allylic functionalisation reactions will be developed in the presence of non-noble copper or selenium catalysts from terpenes for rapid access to molecular units of the guaianolide family.