A representative Lewis base organic catalyst (9‐amino‐9‐deoxy epi‐quinine, QNA) can be adsorbed in high yields onto acidic alginate gels (AGs) using a very simple and straightforward protocol. The resulting solvogel beads (QNA@AGs) are active as heterogeneous catalysts in the addition of aldehydes to nitroalkenes, affording the corresponding adducts in good yields and moderate to excellent diastereo‐ and enantio‐selectivities. In these reactions, the carboxylic functions of the biopolymer act as both acidic co‐catalyst and non‐covalent anchoring site for the tertiary amine catalyst (as observed by IR spectroscopy). Use of heterocationic gels, derived from alkaline earth metal gels by proton exchange, provided materials with better mechanical properties and higher porosities, ultimately resulting in higher catalytic activities. This work represents the first utilization of alginates, abundant and renewable biopolymers, as gel supports/media for asymmetric organocatalytic processes.
The Front Cover shows in the center an alginate gel bead with 9‐amino (9‐deoxy)epi‐quinine (QNA) immobilized thanks to the non‐covalent interactions with the carboxylic groups of the support. The bead is held by two hands that emerge from the seabed. These hands represent the high enantioselectivity of the catalyst as well as its ability to be recovered, making the system fully heterogeneous for a model asymmetric reaction. The algae behind the hands represent the brown macroalgae, the natural source of the alginate. Likewise, the technique chosen for this cover was watercolor due to the association between the sea and the renewable feature of the catalyst precursors. [Artwork and design by Alejandra Aguilera] More information can be found in the Full Paper by L. Bernardi, N. Tanchoux et al.
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