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Abstract :
[en] Carbon dioxide (CO2) is a greenhouse gas responsible for global warming. In the last decades, efforts have been put towards the valorization of this abundant, nontoxic inexhaustible C1 source for the synthesis of useful commodity chemicals. The synthesis of cyclic carbonates is attracting much interest due to its 100% atom efficiency reaction and its large potential scope for the design of complex organic molecules or novel functional polymers (polycarbonates, polyurethanes, etc.). 5-membered cyclic carbonates can be obtained by the coupling of CO2 with diols, epoxides and lastly, alkynols. The latter have the advantage of affording cyclic carbonates that are activated by the presence of an exocyclic vinylic bond, making them reactive towards alcohols and amines. In addition, their ring-opening is regio-selective affording β -oxo-carbonate by reaction with alcohols, β-oxo-urethanes with secondary amines or β-hydroxy-oxazolidones with primary amines.
Due to the inertness and high thermodynamic stability of CO2, a catalyst is required to transform alkynols into alkylidene cyclic carbonates. Bases, ionic liquids), carbenes, metal salts, have been shown to promote the cyclisation of CO2 with alkynols. Although full conversions are obtained in certain cases, the selectivity remains an issue. Also, harsh conditions and/or excessive amounts of base are often used.
In this work, we designed novel, cheap, highly efficient organocatalysts for the synthesis of α-alkylidene cyclic carbonates from CO2 and alkynols. Several organocatalysts, based on ammonium cations and basic anions were screened, and kinetic studies were performed by Raman spectroscopy to identify the best anion/cation couple. We further optimized our catalytic system by developing cooperative catalysts providing conditions for the selective formation of α-alkylidene cyclic carbonates and oxoalkylcarbonates under mild experimental conditions and short reaction times at low catalyst loading.
