Can electrostatic catalysis of Diels–Alder reactions be harnessed with pH-switchable charged functional groups?

Quantum-chemical calculations at the M06-2X/6-31+G(d,p) and G3(MP2)CC levels of theory are used to assess the feasibility of harnessing charged functional groups to electrostatically catalyse Diels-Alder reactions and alter their regio selectivity. For the reaction of the polar diene 2-pyrone with substituted cyclopentene, pH switches of nearly 60 kJ mol-1 are observed in the gas-phase. To switch regioselectivity however it is necessary to toggle between negatively and positively charged functional groups. With the 6-membered cyclohexene derivatives, similar pH-switches are observed but this time an opportunity to pH-switch diastereomeric selectivity is also observed due to the asymmetry of the transition state. When 2-pyrone was replaced with a non-polar diene, cyclopentadiene, pH switches were understandably smaller but still substantial (ca. 15 kJ mol-1). Likewise pH switches are attenuated by solvent but remain substantial (ca. 30 kJ mol-1) in toluene and synthetically useful (ca. 15 kJ mol-1) even in moderately low polar solvents such as dichloromethane.