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