Thermolytic ring closure reactions of 4‐azido‐3‐phenylsulfanyl‐and 4‐azido‐3‐phenylsulfonyl‐2‐quinolones to 12H‐quinolino‐[3,4‐b][1,4]benzothiazin‐6(5H)‐ones

4-Hydroxy-3-phenylsulfanyl-2-quinolones 2 and 4-hydroxy-3-sulfonyl-2-quinolones 7, which are readily accessible from 4-hydroxy-2-quinolones 1 and diphenyldisulfide or thiophenol, can be converted to 4-azido-3-phenylsulfanyl-2-quinolones 10 or 4-azido-3-phenylsulfonyl-2-quinolones 12 via 4-chloro-3-phenylsul-fanyl-2-quinolones 5 or 4-chloro-3-phenylsulfonyl-2-quinolones 9, respectively. Thermolysis of the azides 10 and 12 results in a cyclization reaction to give quinolino[3,4-b][1,4]benzothiazinone 11 and quino-lino[3,4-b][1,4]benzothiazinone dioxides 13, respectively. The conditions for thermolysis have been studied by differential scanning calorimetry (DSC).