No abstract

Synthesis of 1-Substituted 5-Acetyl (Ethoxycarbonyl)-2,3-dihydropyrazolo[3,4-b]pyridin-3-ones -[via thermal intramolecular cyclization of dihydropyrazolylaminomethylidene β-dicarbonyl derivatives (III)]. -(LEBED*, P. S.; MOZGOVAYA, N. G.; MANOILENKO, O. V.; TOLMACHOVA, V. S.; VOVK, M. V.; Chem. Heterocycl.

Keywords: 5-amino-1-ethoxycarbonyl-1,2-dihydro-1H-pyrazol-3-one, 5-aminopyrazol-3-one, 1,3-dicarbonyl compounds, pyrazolo [3,4-b]pyridin-3-ones, cyclocondensation.Partially hydrogenated pyrazolo [3,4-b]pyridin-3-ones are a biologically important and promising type of fused heterocyclic system. They include compounds with pronounced antispasmodic [1], antidepressant [2], and cytotoxic [3] activity and are also able to inhibit hormone-sensitive lipases [4,5].Two routes have been reported for the construction of this system: annelation of a pyrazole ring to a 2-functionalized nicotinic acid derivatives [6,7] or the condensation of 5-amino-1,2-dihydro-3H-pyrazol-3-one (1) with 1,3-dicarbonyl compounds. With the availability of reagents in mind, the second route is the more acceptable even though the presence in the molecule of compound 1 of three nucleophilic centers is generally a cause of nonselective cyclocondensation so forming, along with the target dihydropyrazolopyridinones, some pyrazolo[1,5-a]pyrimidine derivatives due to participation of the 1-NH and 5-NH 2 groups in the reaction.As a result of the aminodihydropyrazolone 1 reaction with ethyl acetylpyruvate in acetic acid, there has previously been obtained a mixture of ethyl 3-oxo-2,3-dihydropyrazolo[3,4-b]pyridine-4-carboxylate (80% yield) and the corresponding 2,3-dihydropyrazolo[1,5-a]pyrimidin-2-one (10% yield) [8]. However, in many attempts to reproduce this reported method we have found that the content of the latter product is not less than 25-30%. When the same reaction was carried out by us without solvent at 120ºC by another known method [9] it was possible to prepare the target product in a yield no higher that 20%. According to the data in [8, 10] the result of condensation of compound 1 with 3-oxobutanal or 1,3-diketones in acetic acid or hydrochloric acid medium is the formation in all cases of a mixture of the corresponding dihydropyrazolo[3,4-b]pyridine and dihydropyrazolo[1,5-a]pyrimidine. At the same time it was found that the use of the sodium or potassium salt of

Reaction of the title pyrazole‐1‐carboxylate (I) with 1,3‐dicarbonyl compounds or their synthetic equivalents provides a general, regiospecific synthetic route to dihydrapyrazolopyridinones.