Formation of Naphthoquinone Oxo-Pyridinium Inner Salts

When 2-chloro-3-(substitued phenoxy)naphthazarine (1) was treated with pyridine or substituted pyridine at elevated temperature, an unexpected reaction took place. The product was identified as 5,8-Dihydroxy-1,4-dioxo-3-(substituted pyridinium)-2-naphthoxide (3, 4). A reaction mechanism for the formation of this product was postulated.