Selective Lewis Acid Complexation of 2-Hydroxyethyl Esters using Competitive Diels–Alder Reactions as a Mechanistic Probe

Competitive Diels–Alder reactions involving ethyl acrylate, 2-hydroxyethyl acrylate and 2-methoxyethyl acrylate indicate that certain Lewis acids (e.g. EtAlCl2) selectively complex to the 2-hydroxyethyl ester group. Studies using ethyl 2-hydroxyethyl fumarate support these findings. 13C NMR spectroscopy provides some evidence regarding the nature of the interactions between 2-hydroxyethyl esters and EtAlCl2. The influence of EtAlCl2 on the level of diastereocontrol observed in the Diels–Alder reactions of (2R∗,3R∗)-2-(3-hydroxy)butyl acrylate is described.