N-arylphthalazinium cations: synthons for biphthalazinylidenes via endocyclic phthalazinium ylide intermediates

Abstract

Treatment of 2-aryl-1 -hydroxy-1,2-dihydrophthalazines with HClO₄ in MeCN gave 2-N-arylphthalazinium cations as perchlorate salts. These, when heated with NaOAc in MeCN gave good yields of biphthalazinylidenes via an endocyclic 2-arylphthalazin-2-ium-1 -ide intermediate. The presence of the ylide intermediate is supported by deuterium protium exchange at C-1 in the phthalazinium cation. At ambient temperature in water some nucleophiles added to the cations to give 1 -substituted-2-aryl-1,2-dihydrophthalazines.