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Browsing by Subject "mikroaalto"

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  • Vesterinen, Johanna (2012)
    Pyrazoles are five-membered nitrogen containing heterocycles, whose derivatives can be widely used in medicinal chemistry. One of the most common ways to produce pyrazoles is 1,3-dipolar cycloaddition, where the dipole containing heteroatom is reacting with a dipolarophile, and forming a cycloadduct. Among others, mesoionic sydnones have been used as dipoles in 1,3-dipolar cycloadditions of pyrazoles. During the last decades solid phase methods, where either a dipole or dipolariphile is being temporarily bound to solid support, have been exploited in 1,3-dipolar synthesis. With the aid of solid phase methods, the synthesis can be controlled chemically by protecting groups that react easily. Also the isolation and purification can be made easier by using these techniques. The 1,3-dipolar solid phase methods can be combined with microwave techniques, to make the synthesis shorter and more effective. The goal of this work was to synthesize new N-unsubstituted pyrazoles, starting from sydnones bound to solid support and alkynes, with use of 1,3-dipolar cycloaddition reaction and to purify and analyze prepared compounds. The aim was also to develop a new 1,3-dipolar solid phase method so, that the end products could be cleaved easily in a traceless manner, and that there would be minor need for purification. There was also an aim to make the last step of the synthesis faster and easier with microwave reactor, and by using this method to standardize the conditions used in the cycloaddition-dehydration reaction step. The AMEBA-resin was chosen to be the solid support in this synthesis. Its traceless cleavage by trifluoroaceitic acid made possible not only the formation of the desired structure, but also effortless purification of the end product. The amino group of pyrazole was protected by the solid support during the N-nitrosation, so that after the traceless cleavage of the resin, N-unsubstituted pyrazoles were obtained. By changing the amino acids used in this synthesis, it was possible to alter the structure of the synthesized pyrazoles, and to create four structurally new pyrazoles. Microwave method used during the last step of synthesis for heating shortened the reaction step significantly, and also the yields of end products were better compared to conventional heating. During this work a functioning and developable 1,3-dipolar solid phase method was created, that can be utilized to synthesize pyrazoles and other compound of similar nature also the in future.