Synthesis and structural characterisation of 4H‐1,3‐benzothiazine derivatives

The ring‐closure reactions of N‐arylthiomethylaroylamide derivatives ( 1a‐g ) in the presence of phospho ‐rus oxychloride gave 2‐aryl‐4H‐1,3‐benzo‐thiazines (2a‐g). 2‐(3‐Chlorophenyl)‐6‐methyl‐4H‐1,3‐benzoth‐iazine ( 2b ) was reduced with Zn to obtain the corresponding 2,3‐dihydro derivative ( 3b ). Potassium permanganate oxidation of 2‐(4‐chlorophenyl)‐2,3‐diethoxy‐4H‐ ( 2e ) and 2‐(2‐fluorophenyl)‐6,7‐diefhoxy‐4H‐1,3‐benzo‐thiazines ( 2g ) gave the corresponding 4‐ones ( 4e,g ). The reactions of 2‐(4‐chlorophenyl)‐6‐mefhyl‐4H‐1,3‐benzofhiazine ( 2c ) with substituted acetyl chlorides led to linearly condensed ß‐lactams ( 5a,b ). The structures of the compounds studied were confirmed by ¹H and ¹³C NMR and by their characteristic mass spectrometric fragmentations.