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 NaClO 4 ( 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.