Theoretical Study on Chiral Boron Complex-Promoted Asymmetric Diels-Alder Cycloadditions

The Diels-Alder reaction is a very interesting process that has been deeply studied in its achiral version. More recently, in its chiral version, it has also been the focus of many experimental and theoretical reports. Here, we study the Diels-Alder reaction of 2 '-hydroxychalcones, as dienophiles, with two dienes, catalyzed by chiral organo-boron Lewis acid complexes. We theoretically evaluate the mechanism that has been empirically proposed in the literature, and we clarify several results that didn't allow the full rationalization of the experimental data. Therefore, we show that similar ligands in the complexes lead to quite different enantioselectivities, due to different steric interactions with the attacking diene. In addition, we also conclude that the low endo/exo selectivities result from two opposite effects in the Diels-Alder transition states of the endo pathways, which substantially increase their activation energy, reaching values very similar to those calculated for the exo transition state structures.

Automated summary

The Diels-Alder reaction is a fascinating chemical process that has been extensively studied, both in its achiral and chiral versions. In this study, the authors investigate the Diels-Alder reaction of 2'-hydroxychalcones with two dienes, catalyzed by chiral organo-boron Lewis acid complexes. The authors use theoretical methods to evaluate the proposed reaction mechanism and provide insights into the enantioselectivity and endo/exo selectivity of the reaction.