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100. Synthetic Use of Thermoanalytical Methods in the Determination of Ringclosure Reaction Conditions and Reaction Mechanisms
H. V. Dang, A. E. Täubl, W. Stadlbauer, in Proceedings of ECSOC-9, The Eighth International Electronic Conference on Synthetic Organic Chemistry, http://www.mdpi.org/ecsoc-9.htm, November 1-30, 2005; J. A. Seijas, M. P. Vázquez-Tato (Eds). CD-ROM edition, ISBN: 3-906980-16-2; MDPI, Basel, Switzerland, 2005.

Thermal induced reactions can be planned and elucidated by thermoanalytical methods such as differential scanning calorimetry (DSC) or thermogravimetric analysis (TGA). In this contribution we report about the determination of reaction and cyclization temperatures by DSC methods and the elucidation of the reaction mechanism by TGA methods. Azidoarenes with suitable ortho groups such as aryl- or acyl substituents cyclize thermally to give five-membered rings such as indoles or isoxazoles. The reaction temperature is varying depending on the ortho-group and can determined by means of DSC. It can be shown that solvents lower the cyclization temperature for about 50 °C. o-Nitrohetaryl-malonates of type 3 were found to cyclize on thermal treatment to give isoxazoles by loss of methanol and CO2. The reaction was studied by DSC and TGA in order to elucidate the reaction mechanism.

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