N-Acyliminium ions of the 2-aza-1, 5-hexadienyl type frequently rearrange to isomeric ions by a process which is formally a 2-ma-Cope rearrangement. When gem-dimethyl substitution is present at C-4 of the initially formed N-acyliminium ion, the rearranged ion cyclizes to afford a substituted pyrrolidine. This rearrangement-cyclization can be used to prepare pyrrolizidinones and indolizidinones and has been applied to enantioselective ...
