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87. 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 (Organic Azides in Heterocyclic Synthesis, Part 31)
Anna E. Täubl, Klaus Langhans, Thomas Kappe and Wolfgang Stadlbauer J. Heterocyclic Chem. 39, 1259-1264 (2002).

Abstract: 4-Hydroxy-3-phenylsulfanyl-2-quinolones and 4-hydroxy-3-sulfonyl-2-quinolones , which are readily accessible from 4-hydroxy-2-quinolones 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-phenylsulfanyl-2-quinolones or 4-chloro-3-phenylsulfonyl-2-quinolones, respectively. Thermolysis of the azides 10 and 12 results in a cyclization reaction to give quinolino[3,4-b][1,4]benzothiazinone 11 and quinolino[3,4-b][1,4]benzothiazinone dioxides 13, respectively. The conditions for thermolysis have been studied by differential scanning calorimetry (DSC).

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