Reactions of <i>o</i>‐aminonitriles with isocyanates. 2. A facile synthesis of imidazo[1,2‐<i>c</i>]quinazoline‐2,5‐(3<i>H</i>,6<i>H</i>)dione

Abstract

Abstract Anthranilonitrile reacts with ethyl isocyanatoacetate to form 2‐(3‐ethoxycarbonylmethylureido)benzonitrile (3b) which, upon heating, or treatment with a base, undergoes a double cyclization to yield imidazo[1,2‐ c ]‐quinazoline‐2,5‐(3 H ,6 H )dione ( 5 ) in excellent yield. In the presence of acid, 3b is converted into 1,4‐dihydro‐2,4‐dioxo‐3‐(2 H )quinazolineacetic acid ( 11 ), or its ethyl ester ( 10 ). The action of concentrated sulfuric acid converts the adduct 13 of anthranilic acid and ethyl isocyanatoacetate into 2‐ethoxycarbonyl‐methylamino‐4 H ‐3,1 ‐benzoxazin‐4‐one ( 14 ).