Due to the availability of a comprehensive set of experimental reference data, the Diels-Alder reaction under pressure has been scrutinized extensively with ab initio simulation techniques. Jha and co-workers, for example, studied the Diels-Alder reaction of butadiene and ethylene at pressures up to 1.4 GPa using G-FMPES in combination with hybrid DFT and multireference wavefunction-based methods. It was found that hydrostatic pressure leads to a lowering of the activation energy barrier and to its eventual disappearance if the pressure is high enough. This finding is in agreement with a recent work on the Diels-Alder reaction of cyclopentadiene and ethylene, in which GOSTSHYP was used to apply pressure both statically via DFT and dynamically via AIMD simulations. This study demonstrated that low pressure leads to a compression of the van der Waals complex of the reactants before the reaction becomes barrierless at higher pressures. Due to random thermal oscillations, the point in time at which the product is formed at a given pressure is variable.