Can Electron Transmission from Aza‐Crown Ethers Contribute to Diels‐Alder π‐Facial Selectivity?

A pair of isodicyclopentafulvenes that carries an exocyclic phenyl group para‐substituted with an aza‐15‐crown‐5 or aza‐18‐crown‐6 ring has been prepared. These molecules (5a and 5b) and their respective NaClO4 (11) and KSCN (12) complexes were examined for the extent of π‐facial stereoselectivity operational during their Diels‐Alder cycloaddition to (Z)‐1,2‐bis(phenylsulfonyl)ethylene (2) under conditions of high pressure. Whereas 5a and 5b engage in [4 + 2] condensation with a 2.5–3.1 preference for dienophile capture from the above‐plane direction, their complexes show a substantially reduced tendency for doing so (14/13 = 1.2–1.4). However, this response goes contrary to those para‐substituent effects previously observed. The linear correlation noted earlier conformed to an increased preference for above‐plane cycloaddition to 2 as the para‐substituent became progressively more electron‐withdrawing. Probable reasons for this seemingly divergent behavior are presented.