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- Title
Synthesis and Structural Identification of 5-Amino-4-hydroxyiminopyrazoles and (E)- N1-Aryl-3-aryl-4- [(substituted pyrazolyl)diazenyl] Pyrazoles from 5-Aminopyrazoles with Ethyl Nitrile.
- Authors
Naoto Uramaru; Li-Ya Wang; Hui-Hsuan Chiang; Fung Fuh Wong
- Abstract
Pyrazoles play an important role among a wide variety of nitrogen heterocycles that have been used for developing useful agrochemicals and pharmacological agents. Furthermore, active nitroso compounds have also played significant roles in the synthesis of many biologically active heterocyclic compounds in organic chemistry and served as important chiral ligands or chiral auxiliaries for asymmetric synthesis. Therefore, 5-amino-4-nitrosopyrazole compounds, which graft nitroso group on the pyrazolic ring, were developed to constitute an efficient synthesis of 5-substituted imidazo[4,5-c]pyrazoles as CNS depressants or pyrazolo[3,4,-b]pyrazine. We have developed the conveniently one-pot synthesis method to give the 5-amino-4-hydroxyiminopyrazole and (E)-N1-aryl-3-aryl-4-[(substituted pyrazolyl)diazenyl]pyrazole as the corresponding products by reacting 5-aminopyrazoles with ethyl nitrile (10-20 wt% in EtOH) in presence of 10% HCl(aq).Scheme 1 shows the typical reaction condition of the one-pot synthesis for 5-amino-4-hydroxyiminopyrazole and (E)-N1-aryl-3-aryl-4- [(substitutedpyrazolyl)diazenyl]pyrazoles. The new procedure involved the treatment of 5- aminopyrazole with ~3.0 equivalent of ethyl nitrile in EtOH solution at room temperature for 10-30 mins. The clearly resulting solution was cooled and added with 10% aqueous hydrochloride acid for stirring within 0.5-1.0 h. While the starting material was consumed, the resulting mixture was concentrated under reduced pressure and worked-up. Consequently, the residue was charged onto the column in a little CH2Cl2 and the solvent could percolate down to the surface of silica gel. The column was eluted with EtOAc/n-Hexane (2:8). At first diazenylpyrazole band eluted from the column and then 5-amino-4-hydroxyiminopyrazole green band was sequentially eluted and isolated in high purity. The reaction gave a mixture of5-amino-4-hydroxyiminopyrazoleand the significant amount of coupling dimeric diazenylpyrazole, respectively (see Scheme 1). We have successfully developed the one-pot reaction to prepare 5-amino-4-hydroxyiminopyrazole and diazenylpyrazole derivatives by treating 5- aminopyrazoles with ethyl nitrile in presence of 10% HCl(aq). Following the further single-crystal X-ray diffraction study (ORTEP), the 5-amino-4-hydroxyiminopyrazole tautomer structure was first determined and demonstrated. This newly presented 5-amino-4-hydroxyiminopyrazole was opposed to the previous nitroso structure.
- Subjects
PYRAZOLES; BIOACTIVE compounds; NITROSO compounds; ORGANIC chemistry; ORGANIC compounds; IMIDAZOPYRIDINES
- Publication
Current Trends in Biotechnology & Pharmacy, 2020, p115
- ISSN
0973-8916
- Publication type
Article