Disruption of the three-dimensional network of suberin in cork by cholinium hexanoate leads to its efficient and selective isolation. The reaction mechanism, which likely involves selective cleavage of some intermonomeric bonds in suberin, was still unanswered. To address this question, the role of the ionic liquid during suberin depolymerisation and during cleavage of standard compounds carrying key chemical functionalities was herein investigated. A clear demonstration that the ionic liquid catalyses the hydrolysis of acylglycerol ester bonds was attained herein, both experimentally and computationally (DFT calculations). This behaviour is related to cholinium hexanoate capacity to activate the nucleophilic attack of water. The data showed also that the most favourable reaction is the hydrolysis of acylglycerol ester bonds, with the C2 position reporting the faster kinetics, whilst most of the linear aliphatic esters remained intact. The study emphasises that the ionic liquid plays the dual role of solvent and catalyst and leads to suberin efficient extraction through a mild depolymerisation. It is also one of the few reports of ionic liquids as efficient catalysts in the hydrolysis of esters.

The mechanism proposed by Evans for the dialkylaluminum chloride promoted Diels-Alder reaction of cyclopentadiene with alpha,beta-unsaturated N-acyloxazolidinones has been widely used as a basis for the rationalization of the experimental selectivities observed in many different types of reactions in which oxazolidinones or imidazolidinones are used as chiral auxiliaries. In this manuscript we introduce a new and more general model based on molecular modeling and NMR spectroscopy data that avoids several ambiguous concepts raised by the Evans model and fully explains all available experimental data. While the Evans proposal relies on the formation of high-energetic ionic chelates that promote the rotation of the amide bond in the N-acyloxazolidinone molecule, our model is based on the catalysis by means of low-energetic mono- or bicomplexes at the chain and the ring carbonyl groups that are easily observed by NMR spectroscopy measurements. The observed selectivities are explained by a chirality-transfer concept, in which an achiral Lewis acid works as a bridge for the transfer of chirality between a chiral auxiliary and a prochiral reactive center. Different to the Evans proposal, this mechanism fully explains the experimental selectivities for low Lewis acid concentrations, based on the catalysis by means of concurrent monocomplexes at the chain or the ring carbonyl groups, as well as the increased reaction rates and selectivities experimentally observed for high Lewis acid concentrations. The model can be extrapolated to nonchelating and other chelating Lewis acids, thereby allowing for the rationalization of much experimental data that were never explained by the Evans proposal.

Transition states associated with the C-C bond-formation step in proline-catalyzed intramolecular aldol reactions of 1,7-dialdehydes were studied using density functional theory methods (DFT), at the B3LYP/6-31G(d,p) level. A polarizable continuum model (PCM) was used to describe solvent effects. Two reactive channels, corresponding to the anhydrous system or to the explicit inclusion of water have been analysed.

The mechanisms of proline-catalyzed and imidazole-co-catalyzed intramolecular Baylis-Hillman reactions have been studied by using density functional theory methods at the B3LYP/6-31G(d,p) level of theory. A polarizable continuum model (PCM B3LYP/6-31++G(d,p)//B3LYP/6-31G(d,p)) was used to describe solvent effects. Different reaction pathways were investigated, which indicated that water is an important catalyst in the imine/enamine conversion step in the absence of imidazole. When imidazole is used as a co-catalyst, water is still important in the imidazole addition step, but is not present in the Baylis-Hillman cyclization step. The computational data has allowed us to rationalize the experimental outcome of the intramolecular Baylis-Hillman reaction, validating some of the mechanistic steps proposed in the literature, as well as to propose new ones that considerably change and improve our understanding of the full reaction path.