Overcoming the Reversibility in the Diels-Alder Reaction of Bio-Based Electron-Poor Furans with Maleimides Through Liquid-to-Solid Phase Transition.

In the chemistry of bio-based furans, the Diels-Alder reaction plays an important role as a renewable route for the synthesis of fuels, fine chemicals, and monomers. Nonetheless, the unfavorable kinetic and thermodynamic parameters inherent to the Diels-Alder reaction involving furans as dienes often lead to the reversibility of cycloaddition, resulting in decreased equilibrium conversion and diastereoselectivity. In this study, we present a new strategy for overcoming the problem of reversibility in chemical reactions. We demonstrate that conducting the reaction under solvent-free conditions can facilitate the transition from a molten state formed by the initial reactants to a solid phase containing the reaction product along with an excess of the initial substrate. According to our results, such a liquid-to-solid transition of the reaction mixture can lead to exceptionally high conversion and diastereoselectivity in the furan-maleimide Diels-Alder reaction, particularly for challenging electron-poor furanic substrates. Our approach enables the reversible furan-maleimide Diels-Alder reaction to be performed in a cleaner and more environmentally friendly manner, free from the complexities associated with the use of solvents and the need for purification from side products.