Fig. 7. (a) Free energies (normal text) and enthalpies (bold, italic) calculated at SMD(DCM)-M06-2X/6-31G(d) are in kcal mol–1 relative to separated reactant species shown. Values inside parentheses represent free energies without explicit base. An explicit base (2,6-lutidine) was modelled to study stereoelectronic effects on TSSs involved in the initial DA cycloaddition. (b) Optimized TSSs leading to endo and exo cycloadducts showing π–π stacking and CH–π interactions between the BTM-bound acylammonium salt and the hydrogen-bonded Brønsted base–diene complex. Selected bond distances are shown (Å).
