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65. Ring closure reactions of heterocyclic azides with the assistance of DSC (Organic azides in heterocyclic synthesis, 22)
Dang V.T., Stadlbauer W., Molecules, 1 (1996) 201-206

Abstract: 5-Azido-pyrido[2,3-d]pyrimidine-2,4,7-triones or 6-azido-uracils with reactive ortho-substituents such as aryl-, acyl- or nitro groups were prepared from the corresponding hydroxy compounds by chlorination (or tosylation) and reaction with sodium azide. The azides cyclize thermically to the corresponding indoles, isoxazoles or furoxanes. The cyclization conditions depend upon the structural properties of the ortho-substituents and range between 50 and 150oC. The determination of the reaction temperature and the suitable solvents was carried out with the aid of DSC (Differential Scanning Calorimetry), and also further reactions such as the desoxygenation of the obtained furoxanes could be investigated by DSC in order to find the suitable reaction conditions. As example the synthesis and thermolysis of an 5-azido-6-phenyl-pyrido[2,3-d]pyrimidine-2,4,7-trione to the corresponding indole is shown in the scheme.

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