Reinvestigation of a 5 H ‐dibenzo[ d,h ][1,3,6]triazonine synthesis

Treatment of 5‐chloro‐2‐aminobenzophenone ( 1 ) with o ‐phenylenediamine, sodium acetate, and acetic acid gave 2‐(acetyl)amino‐5‐chlorobenzophenone ( 5 ) rather than N ‐[(2‐amino‐5‐chlorophenyl)phenylmethylene]‐1,2‐benzenediamine ( 3 ), as reported by Kulkarni et al , [1]. Authentic 3 was prepared and treated with chloroacetic acid and polyphosphoric acid (PPA) to give 1 , recovered 3 , 2,8‐dichloro‐6,12‐diphenyldibenzo[ b,f ][1,5]diazocine ( 9 ) and 2‐chloro‐6‐(chloromethyl)‐13‐phenyl‐5 H ‐dibenzo[ d,h ][1,3,6]triazonine ( 10 ). Treatment of 5 with PPA, with or without chloroacetic acid, gave [5‐chloro‐2‐[(6‐chloro‐4‐phenyl‐2‐quinolinyl)amino]phenyl]phenylmethanone (11) as the sole product in 90% yield. Treatment of other benzophenones, acetophenones, and anilines with sodium acetate and acetic acid provided acetanilides in 78‐96% yield, with the exception of 2′‐aminoacetophenone ( 20 ), which gave a quantitative yield of 2‐[((2‐acetyl)phenyl)amino]‐4‐methylquinoline ( 21 ). The mechanism of acetanilide formation with sodium acetate and acetic acid is discussed. The structure of 21 was established using high resolution 1 H nmr techniques. Attempts to prepare an authentic sample of 21 from 2‐chlorolepidine ( 26 ) and ( 20 ) gave 4‐methyl‐ N ‐[2‐(4‐methyl‐2‐quinolinyl)phenyl]‐2‐quinolinamine ( 29 ) as the major product.