Nitropyrazoles

A method of preparation of 5-amino-3,4-dinitropyrazole (1) from 3(5)-methyl-5(3)-nitro- and 3(5)-methyl-4,5(3)-dinitropyrazoles was developed, the key step of which was the Hofmann rearrengement of nitro- and dinitropyrazolecarboxamides. The protonation of 5-amino- 3,4-dinitropyrazole was studied by spectral methods (UV spectroscopy, NMR spectroscopy). In spite of low basicity of the amino group, compound 1 undergoes N-arylation, N-nitration, and annulation reactions with formation of dinitropyrazolo[5,1-a]pyrimidine derivatives and hitherto unknown dinitroimidazo[1,2-b]pyrazole derivatives. Diazotization of 1 leads to 5-diazo-3,4-dinitropyrazole (19), which exists in the form of the internal salt. Some reactions of this compound were studied and the formation of the corresponding 5-halogeno(azido)- 3,4-dinitropyrazoles under the action of the halide and azide ion was shown. Dinitropyrazolo- [5,1-c][1,2,4]triazine and 7-hydroxydinitro-4,7-dihydropyrazolo[5,1-c][1,2,4]triazine deriva- tives were obtained by the action of active methylene compounds on the betaine 19.     

Liquid-phase synthesis of combinatorial libraries based on 7-trifluoromethyl-substituted pyrazolo[1,5-a]pyrimidine scaffold

The parallel solution-phase synthesis of more than 2200 7-trifluoromethyl-substituted pyrazolo[1,5-a]pyrimidine and 4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine carboxamides on a 50-100-mg scale has been accomplished. Key reactions include assembly of the pyrazolo[1,5-a]pyrimidine ring by condensation of 5-aminopyrazole derivatives with the corresponding trifluoromethyl-beta-diketones. The libraries from libraries were then obtained in good yields and purities using solution-phase acylation and reduction methodologies. Simple manual techniques for parallel reactions using special CombiSyn synthesizers were coupled with easy purification procedures (crystallization from the reaction mixtures) to give high-purity final products. The scope and limitations of the developed approach are discussed.