Kinetics and mechanisms of nucleophilic displacements with heterocycles as leaving groups. Part 12. Regio- and stereo-chemistry of nucleophilic displacement and solvolysis reactions of N-(α-methylallyl)-and N-(α-phenylethyl)-pyridiniums

Abstract

N-(α-Methylallyl)pyridiniums rearrange to the N-(γ-methylallyl) analogues in a process analogous to ion return. In the tricyclic series the process (9)→(4) occurs spontaneously. In the monocyclic series (1) can be isolated and thermally rearranged into (2); this rearrangement is intramolecular. N-(α-Phenylethyl)pyridiniums solvolyse in HOAc–NEt₃ with predominant inversion of configuration (90%). In the 2,4,6-triphenyl series this occurs spontaneously. The isolated 1-(α-phenylethyl)-2-isopropyl-4,6-diphenylpyridinium solvolyses in chlorobenzene with first-order kinetics and with racemisation.