Studies on intramolecular cycloadditions involving 3-oxidopyridinium

Abstract

3-Oxidopyridinium derivatives bearing a pendant pent-4-enyl group at either N-1 or C-2 undergo intramolecular cycloadditions to form tricyclic systems. The chemistry of these cycloadducts has been explored, and that from the 2-substituted series compared to the cycloadduct from the corresponding pyrylium analogue; the nitrogen containing systems exhibit different chemical reactions in which the nucleophilicity of the nitrogen atom dominates. Quaternisation of the nitrogen atom and base treatment leads to opening of the aza-bridge. In contrast to the oxygen containing systems, no skeletal rearrangements (e.g. of the perhydroazulene to decalin type) were observed.