Sodium ascorbate as an expedient catalyst for green synthesis of polysubstituted 5-aminopyrazole-4-carbonitriles and 6-amino-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles

Abstract

Sodium ascorbate (SA) was used as a safe catalyst for the synthesis of 5-aminopyrazole-4-carbonitriles from the one-pot three-component cyclocondensation (3-CC) of aldehydes, phenylhydrazine, and malononitrile at 50 °C. This 3-CC proceeds in a mixture of ethanol–water as a green reaction medium to give the desired densely functionalized pyrazoles in good to high yields. 6-Amino-1,4-dihydropyrano-[2,3-c]pyrazole-5-carbonitriles were also synthesized in the presence of SA via an eco-friendly and simple four-component cyclocondensation (4-CC). This 4-CC performed in refluxing water as a green medium and dihydropyrano-[2,3-c]pyrazole products were obtained in excellent yields and relatively shorter reaction times. These environmentally friendly multicomponent cyclocondensations offer some interesting advantages, including time-saving, easily available starting materials, mild conditions, minimizing the amount of waste, good atom efficiency, avoiding hazardous organic solvents or catalysts, and the ease of the work-up.