New cyclisation reactions of 3-aminopyrazole derivatives

• Main Author: Mares, Richard W.
• Published: University of Edinburgh 1993
• Subjects: 547.59
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657307

Three synthetic routes to cyclised pyrazole derivatives were investigated:- The first route was based on the chemistry of 2,3-diaminopyrazoles. Reactions with various electrophiles were carried out and some cyclised products were obtained. An important reaction with carbon disulphide was carried out and this resulted in the formation of the photographically important pyrazolo[1,5-<i>b</i>]1,2,4-triazole ring system. The second route explored the chemistry of 3-acetamidopyrazoles. Monoacylation of 3-aminopyrazoles was found to give a mixture of 1- and 2-acylated aminopyrazoles. The mixture surprisingly underwent a solid state rearrangement to the required 3-acetamidopyrazole derivative over a period of a few days. The mechanism and kinetics of this reaction were investigated by solid state and traditional NMR methods. The third route involved the preparation and pyrolysis of pyrazol-3-yl-1,2,3-triazoles to give carbene intermediates which could cyclise. These carbenes were found to undergo a rearrangement to give the pyrazolo[1,5-<i>b</i>]pyrimidin-7-one ring system. The mechanism of this reaction was extensively investigated by isotopic labelling methods.