The synthesis of oxazolo[3,2-a]pyridinium salts

Abstract

A synthesis of 2-substituted oxazolo[3,2-a]pyridinium salts is described. The appropriate 2-(4-ethoxybutyryl)-oxazoles are treated with hydrobromic acid and then cyclised and aromatised by boiling acetic anhydride. Attempts to prepare 2-substituted oxazoles suitable for the synthesis of the parent oxazolopyridinium ion have been unsuccessful. Catalytic reduction of two oxazolopyridinium salts leads to ring opening giving N-substituted 2-piperidones.