Highly Active Potential Antituberculotics: 3‐(4‐Alkylphenyl)‐4‐thioxo‐2 H ‐1,3‐benzoxazine‐2(3 H )‐ones and 3‐(4‐Alkylphenyl)‐2 H ‐1,3‐benzoxazine‐2,4(3 H )‐dihiones Substituted in Ring‐B by Halogen

A series of 6‐chloro‐3‐(4‐alkylphenyl)‐4‐thioxo‐2 H ‐1,3‐benzoxazine‐2(3 H )‐ones, 7‐chloro‐3‐(4‐alkylphenyl)‐4‐thioxo‐2 H ‐1,3‐benzoxazine‐2(3 H )‐ones, 6‐bromo‐3‐(4‐alkylphenyl)‐4‐thioxo‐2 H ‐1,3‐benzoxazine‐2(3 H )‐ones, 6,8‐dibromo‐3‐(4‐alkylphenyl)‐4‐thioxo‐2 H ‐1,3‐benzoxazine‐2(3 H )‐ones, 6‐chloro‐3‐(4‐alkylphenyl)‐2 H ‐1,3‐benzoxazine‐2,4(3 H )‐dithiones, 7‐chloro‐3‐(4‐alkylphenyl)‐2 H ‐1,3‐benzoxazine‐2,4(3 H )‐dithiones, 6‐bromo‐3‐(4‐alkylphenyl)‐2 H ‐1,3‐benzoxazine‐2,4(3 H )‐dithiones and 6,8‐dibromo‐3‐(4‐alkylphenyl)‐2 H ‐1,3‐benzoxazine‐2,4(3 H )‐dithiones was synthesized. The compounds exhibited in‐vitro activity against Mycobacterium tuberculosis, M. kansasii (two strains), and M. avium. 6‐bromo‐3‐(4‐propylphenyl)‐4‐thioxo‐2 H ‐1,3‐benzoxazin‐2(3 H )‐one and 6‐bromo‐3‐(4‐propylphenyl)‐2 H ‐1,3‐benzoxazin‐2,4(3 H )‐dithione are the most active compounds against M. tuberculosis . The activity is similar to isoniazid (INH). The compounds under study have a broad spectrum of activity against potential pathogenic strains. The replacement of the oxo group by thioxo group of 3‐(4‐alkylphenyl)‐2 H ‐1,3‐benzoxazine‐2,4(3 H )‐diones often led to an improvement in the antimycobacterial activity against M. tuberculosis .