Studies of intramolecular cyclizations of N-acyliminium ions derived from acyclic ketones: unanticipated stereochemical and structural results.

[reaction: see text] Intramolecular cyclizations of a series of (E)- and (Z)-olefinic acyclic ketone-derived N-acyliminium ions have been studied. It has been found that both the course of the reaction and the stereochemistry of the products are critically dependent upon the tether length and olefin geometry of the cyclization substrate.