The Diels–Alder Reaction between Euparin and Dimethyl Acetylenedicarboxylate; a Joint Experimental and Density Functional Theory Study

Abstract

In this project, we have investigated the Diels–Alder (DA) reaction between euparin (as a natural furan derivative) and dimethyl acetylenedicarboxylate (DMAD) as an electrophilic acetylene. The experimental observations during the reaction in different conditions showed that the yield and the rate of the process would increase with increasing the polarity of the solvent. Such observation suspected us that like several recent reports, the mechanism of this DA reaction takes place through a stepwise route containing a zwitterionic intermediate or at least through a relatively polar transition state (TS). Next, during the density functional theory (DFT) studies and the potential energy surface (PES) investigations, we have detected a stepwise reaction pathway in parallel with the one-step route. The results of this work are in agreement with the recent reports about the competition between the one-step and multisteps routes in the DA reactions.