Synthesis of 1 H ‐naphth[2,3‐ d ]imidazole‐4,9‐diones by acid catalyzed cyclization of 2‐Acylamino‐3‐amino‐1,4‐naphthoquinones

The conversion of 2‐acylamino‐3‐amino‐1,4‐naphthoquinones (II) to the corresponding 2‐substituted 1 H ‐naphth[2,3‐ d ]imidazole‐4,9‐diones (I) under both alkaline and acid catalyzed conditions has been effected and the results compared. Treatment of 3‐(4′‐chlorobutanonyl‐amino)‐3‐amino‐1,4‐naphthoquinone (He) with aqueous ethanolic sodium hydroxide solution gives 1,2‐butanonaphth[2,3‐ d ]imidazole‐4,9‐dione (V); whereas, treatment of lie with refluxing formic acid gave 2‐(4′‐chlorobutyl)‐1 H ‐naphth[2,3‐ d ]imidazole‐4,9‐dione. Treatment of 2‐substi‐tuted 1 H ‐naphth[2,3‐ d ]imidazole‐4,5‐diones in DMF with alkyl halides in the presence of potassium carbonate affords the expected 1,2‐disubstituted naphth[2,3‐d]imidazole‐4,9‐diones (VI). The spectral properties of I, II, V and VI as well as those of some 2‐acylamino‐3‐chloro‐1,4‐naphthoquinones IV are discussed.