We start by demonstrating that the level of theory used in this study can predict relative standard activation free energies (∆G •, ‡ ) that are in good agreement with experiment. The relative standard activation free energy is calculated as the difference in Gibbs free energy of TS3 and the reactants at the B3LYP-D3/6-31+G(d,p)(SMD) level. Here, for each catalyst, 50 conformers of TS3 are embedded using a template as previously described and an RMSD pruning cutoff of 0.1 Å is used before each conformer undergoes a constrained GFN2-xTB optimisation where the atoms corresponding to the template are fixed. Furthermore, 50 conformers of the catalyst on its own are created and the same RMSD threshold is used for pruning and the retained conformers undergo GFN2-xTB optimisation. The lowest energy conformer of TS3 and the catalyst on its own are further optimised using Gaussian16 at the B3LYP-D3/6-31+G(d,p)(SMD) level of theory to the respective transition state or minimum. The transition states are characterised by one imaginary frequency along the reaction coordinate corresponding to the abstraction of a proton from the tertiary carbon by a methoxy fragment.