A new practical synthesis of 3-amino-substituted 5-aminopyrazoles and their tautomerism

TLDR: In this article, it was found that 3-amino-substituted 5-aminopyrazoles can be effectively prepared via hydrolytic decarboxylation of the corresponding 3-5-diaminopyrazole-4-carboxylates under microwave irradiation.

About: This article is published in Tetrahedron.The article was published on 2019-04-12 and is currently open access. It has received 8 citations till now. The article focuses on the topics: Tautomer & Decarboxylation.

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Table 2. Synthesis of 3-amino-substituted 5-aminopyrazoles (3) from 3,5-diaminopyrazole-4carboxylates (5)a

Figure 1. Selected bioactive 3,5-diaminopyrazoles.

Figure 5. Supramolecular association in the crystal of 3i: a view of the supramolecular layer parallel to (1 1 0). The N‒H…N hydrogen bonding and N‒H…π(pyrazole) interactions (see ESI Fig. S3 and Table S2†) are shown as orange and blue dashed lines, respectively. Only acidic hydrogen atoms and ipso-carbon atoms of the phenyl groups are shown.

Figure 2. (a) and (b) The molecular structures of the first and second independent molecules comprising the asymmetric unit of 3g, respectively, showing atom labelling scheme and 70% anisotropic displacement parameters, and (c) an overlay diagram of the two independent molecules: red image, the molecule shown in (a) and green image, molecule in (b). The molecules are overlapped so that the pyrazole rings are coincident.

Figure 4. Supramolecular association in the crystal of 3g: (a) N‒H…N hydrogen bonding (see ESI Fig. S2 and Table S1†) leading to a supramolecular chain aligned along the b-axis, (b) detail of the amine-N3a‒H…π(phenyl) interaction, (c) a side-on view of the supramolecular layer parallel to (1 0 1) and (d) a plan view of the layer (amine-N3a‒H…π(phenyl) interactions are not shown). Please refer to the text for an explanation of “i”-“vii” in (a)-(c). In all

Figure 3. (a) The molecular structure of the first independent molecule of 3i showing atom labelling scheme and 70% anisotropic displacement parameters and (b) an overlay diagram of the four independent molecules comprising the asymmetric unit of 3i: red image, the molecule shown in (c), green image, molecule “a”, blue, molecule “b” and pink, molecule “c”. The molecules in are overlapped so that the pyrazole rings are coincident.