Transition State π‐Solvation by Aromatic Rings: An Electronic Contribution to Diels–Alder Reaction Diastereoselectivity

Without making any assumptions regarding the ground-state conformation, it was possible to determine the electronic contribution of the substituent R to the Diels–Alder selectivity by comparing alkylation and Diels-Alder reactions involving 1 and 2. π-Stacking interactions, which, however, do not exhibit significant charge-transfer character, are implicated. This was show in part by the observation that, for all substituents that are not capable of π-stacking for steric or electronic reasons, a linear relation was found to exist between alkylation and Diels-Alder selectivities.