Regioselective generation of iminium cation by PET processes: Its in situ trapping by intramolecular nucleophiles and synthesis of some biologically active heterocycles.

Abstract

Efficient, mild and direct route for regiospecific iminium cation is developed by sequential two electron oxidation of several N-alkylated tertiary amines by photoinduced electron transfer processes. The regiospecificity of iminium cation arises from the deprotonation step of amine radical cation to generate α-amino radical which depends on the stereoelectronic factor subject to kinetic acidity of amine radical cation. Iminium cation is efficiently trapped insitu by internal nuleophiles to give cyclic compounds 14–18 and 22a–c. Stereoselective synthesis of cis α,α′-dialkylated piperidines and pyrrolidines 30a–c is achieved by nucleophilic opening of tetrahydro-1,3-oxazines 22a–c.