Synthesis of quinazolino‐1,3‐benzothiazine derivatives

The ring‐closure reactions of N ‐(3,4‐dimethoxyphenylthiomethyl)‐2‐nitrobenzamide derivatives 5a,b with phosphoryl chloride gave 4‐(2‐nitrophenyl)‐2 H 1,3‐benzothiazine derivatives 7a,b , which on reduction yielded 4‐(2′‐aminophenyl)‐3,4‐dihydro‐2 H ‐1,3‐benzothiazines 8a,b. Reaction of these compounds with phosgene led to a new heterocyclic ring system, 6 H ,8 H ‐quinazolino[3,4‐ c ][1,3]benzothiazine derivatives 9a,b. The structures of the title compounds were proved via their ir and nmr ( 1 H, 13 C) spectra.