Review on catalytic cleavage of C-C inter-unit linkages in lignin model compounds: Towards lignin depolymerisation

Lignin depolymerisation has received considerable attention recently due to the pressing need to find sustainable alternatives to fossil fuel feedstock to produce chemicals and fuels. Two types of interunit linkages (C–C and C–O linkages) link several aromatic units in the structure of lignin. Between these two inter-unit linkages, the bond energies of C–C linkages are higher than that of C–O linkages, making them harder to break. However, for an efficient lignin depolymerisation, both types of inter-unit linkages have to be broken. This is more relevant because of the fact that many delignification processes tend to result in the formation of additional C–C inter-unit bonds. Here we review the strategies reported for the cleavage of C–C inter-unit linkages in lignin model compounds and lignin. Although a number of articles are available on the cleavage of C–O inter-unit linkages, reports on the selective cleavage of C–C inter-unit linkages are relatively less. Oxidative cleavage, hydrogenolysis, two-step redox-neutral process, microwave assisted cleavage, biocatalytic and photocatalytic methods have been reported for the breaking of C–C inter-unit linkages in lignin. Here we review all these methods in detail, focused only on the breaking of C–C linkages. The objective of this review is to motivate researchers to design new strategies to break this strong C–C inter-unit bonds to valorise lignins, technical lignins in particular

Production de jeunes bovins maigres ou engraissés en Limousin : campagne 1987-88

[Coll_IRSTEA]Coll. Etudes du Cemagref, Groupement de Clermont-Ferrand, n° 12

Avenir d'une zone rurale fragile dans le Massif Central : quatre communes au coeur du Parc Naturel des Volcans d'Auvergne

What will happen to the uncultivated lands of retired farmers of the Volcans d'Auvergne park? In order to answer this question, the different elements of the rural environment, their relationships and particularly their relationship with the open space should be taken into account. This study includes a presentation of the physical, human environments and the economic activities of the small region on one hand, and evolution scenariis in 5 and 15 years on the other hand. / Qu'adviendra-t-il des terres libérées par les agriculteurs du Parc des Volcans d'Auvergne (l'étude porte sur 4 communes) qui vont prendre leur retraite ? Pour répondre à cette question il est nécessaire de prendre en compte l'ensemble des composantes du milieu rural et leurs relations, en particulier leur rapport avec l'espace. L'étude comprend ainsi d'une part une présentation du milieu physique, humain et des activités économiques de la petite région aujourd'hui et d'autre part des scénarios d'évolution "au fil de l'eau" à terme de 5 et 15 ans

A Highly Convergent Total Synthesis of Leustroducsin B

Leustroducsin B exhibits a large variety of biological activities and unique structural features. An efficient and highly convergent total synthesis of Leustroducsin B was achieved in 17 longest linear and 39 total steps by disconnecting the molecule into three fragments having similar levels of complexity. These pieces were connected via a highly efficient chelate-controlled addition of a vinyl zincate to an α-hydroxy ketone and a silicon-mediated cross-coupling. The stereochemistry of the central and western fragments was set catalytically in high yields and excellent de by a zinc-ProPhenol-catalyzed aldol reaction and a palladium-catalyzed asymmetric allylic alkylation