Convenient preparation of N‐substituted 2‐amino‐4H‐3,l‐benzoxazin‐4‐ones and 3‐substituted 2,4(1H,3H)‐quinazolinediones

Room temperature treatment of 2‐(3‐arylureido)benzoic acids (1) and methyl 2‐(3‐alkyl‐, or 3‐arylureido)‐ benzoates (2) with concentrated sulfuric acid leads to N‐substituted 2‐amino‐4H‐3,l‐benzoxazin‐4‐ones (3) in generally very good yields. The isomeric 3‐substituted 2,4(1H,3H)‐quinazolinediones (4) are conveniently made in high yield by the action of aqueous‐ethanolic sodium hydoxide on 2.