Condensation of N-3-substituted 5-pyrazolones with esters of β-keto acids. Synthesis of pyrano[2,3-c]pyrazol-6-ones

N-Substituted 5-pryazolones undergo thermal condensation with esters of β-keto acids, losing water and alcohol molecules, to form N-substituted pyrano[2,3-c]pyrazol-6-ones. The pyran ring in these products is readily cleaved by the action of alkali to give the corresponding salts of unsaturated acids. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 367–372, March, 2006.