Synthesis of NSC‐341,964: An unexpected study on the stability of 2‐aryl‐4 H ‐3,1‐benzoxazin‐4‐ones

Resynthesis of NSC 341,964, which had been assigned structure 1 (1‐[[3‐(7‐chloro‐4‐oxo‐4 H ‐3,1‐benzoxazin‐2‐yl)phenyl]methyl]pyridinium chloride) was approached via 7‐chloro‐2‐(3‐methylphenyl)‐4 H ‐3,1‐benzoxazin‐4‐one ( 5 ) obtained from 3‐methylbenzoyl chloride ( 2 ) and 2‐amino‐4‐chlorobenzoic acid ( 3 ) followed by dehydration in acetic anhydride. Radical bromination provided 6 which with pyridine afforded the bromide analog 7 of 1 . Ion exchange, however, gave ring‐opened benzoic acid 8 rather than 1 . The original sample of NSC 341,964 also proved to be ring‐opened material. However, 7 upon standing exhibited slow hydrolysis to 8 so that the structure of the original NSC 341,964 remains uncertain. A more direct route to compound 8 is also described.