Selective synthesis of functionalized pyrazoles from 5-amino-1H-pyrazole-4-carbaldehydes with sodium nitrite: 5-Amino-4-nitrosopyrazoles and pyrazole-4-carbaldehydes

摘要

A novel and efficient redox reaction was developed to react 5-amino-1H-pyrazole-4-carbaldehyde with sodium nitrite (NaNO2) in an acidic solution (HCl/MeOH) to generate 5-amino-4-nitrosopyrazole, pyrazole-4-carbaldehyde, or diazenylpyrazole selectively. The results showed that 5-amino-4-nitrosopyrazoles were formed as the major product in the diluted acidic solution (<= 2 N HCL in MeOH solution) through redox, formylation, and nitrosation reactions of NaNO2. Intriguingly, pyrazole-4-carbaldehyde was the main product under 6 N HCl in MeOH solution. (C) 2019 Elsevier Ltd. All rights reserved.