Resumen de Aluminum-catalyzed coupling of carbon dioxide and cyclic ethers
Utilization of carbon dioxide as a C1-building block for organic chemistry has become increasingly popular over the last decades.
Chapter 1 provides an overview of the general applications of CO2 and more specifically its reaction with epoxides and derivatives to form cyclic carbonates and carbamates. Furthermore, the aluminum triphenolate catalyst is introduced as a potent system to activate epoxides.
A detailed comparative study on the synthesis of 5MCCs is reported in Chapter 2, where the activity of 15 different binary catalytic systems based on aluminum is compared in the conversion of several terminal and internal epoxides to their respective cyclic carbonate products. This type of benchmarking studies is crucial to properly compare catalytic activities and evaluate the best possible catalyst for a given transformation. Best catalysts were the ones based on porphyrin and triphenolate ligand systems, both in terms of high activity and low preparation cost.
In Chapter 3 the first general methodology for the coupling of oxetanes and CO2 has been developed, forming 6MCCs with high yield and selectivity. These 6MCCs monomers are useful starting materials for polymer synthesis or as building blocks for organic synthesis. We have applied the developed method in the formal synthesis of two linear carbamate based drug molecules.
Chapter 4 describes the nucleophile free conversion of epoxides containing alcohol or amine functionalities, making use of an insitu formed carbonate anion that can ring-open the epoxide. This approach differs from the traditional CO2-epoxide coupling reactions where a nucleophilic additive is used to open the epoxide. This strategy resulted in a broad scope of cyclic carbonate structures that would be difficult to synthesize by conventional methods. In addition by using epoxy amines we were able to acces 5-oxazolidinone based structures, which are interesting scaffolds that can be found in many drug molecules. We applied our methodology in the synthesis of the antidepressant Toloxatone.
Chapter 5 provides an in-depth study on the formation and reactivity of alkyl carbonate anions from epoxy alcohols and CO2.
Although the involvement of alkyl carbonates has been proposed in many catalytic transformations, there is little mechanistic or spectroscopic evidence. Herein we provide a complete description of the reaction mechanism related to the coupling of epoxy alchols and CO2, combining mechanistic experiments, in-situ IR spectroscopy and DFT-analysis. We were able to identify and characterize several crucial reaction intermediates through Xray analysis and IR-spectroscopy.
