Synthesis of Pyrazolo[3,4-b]Pyridine and Pyrido[2′,3′:3,4]Pyrazolo [1,5-a]Pyrimidine Derivatives

Abstract

The synthesis of two series of 1-phenyl and 1H -pyrazolo [3,4-b]pyridine is described. Thus, reacting 5-amino-1phenylpyrazole with chalcone analogues gave 4,6-diarylpyrazolo[3,4-b]pyridine derivatives. While, reacting the same starting material with benzylidene derivatives of ethyl cyanoacetate and malononitrile resulted in 4-oxo and 4aminopyrazolo[3,4-b]pyridine derivatives, respectively. The synthesis of 3-amino-4,6-diarylpyrazolo[3,4-b]pyridines starting from pyridine was also described. Thus, chlorination of 4,6-diarylpyridone derivatives and their subsequent cyclisation with hydrazine hydrate afforded 3-amino-4,6-diarylpyrazolo [3,4-b]pyridines. Reaction of the latter compounds with acetylacetone, ethyl ethoxymethylenecyanoacetate and chalcone analogue gave the tricyclic pyrido[2p,3p: 3,4]pyrazolo[1,5-a]pyrimidines. The structures of the products were confirmed by spectral data.

Synthesis of novel pyrazoline based bis (1,2,3-triazole) scaffolds via click chemistry

“…Moreover, H X appeared as doublet of doublet at δ 4.24 ppm (J XA = 14.8, J XB = 9.6 Hz). 30,52 All the other signals from NMR spectra are in agreement with the proposed structures.…”

Heterocyclizations of β-alkoxy, β-diaminoalkyl, and related β-functionalized enones (enals) with NCN-binucleophiles

“…In turn, most of the known transformations relied on using enones derived from ketoesters 39 (Scheme 32) [197][198][199][200][201][202][203] that were subjected to heterocylizations with (3)5-aminopyrazoles (mostly substituted by alkyl, aryl, halogen, nitrile and nitro groups), or diazo diaminopyrazoles [204,205]. Other reported reactions included enones derived from malonates 41 [206][207][208] or cyanoacetates 36 [208][209][210][211][212][213][214], haloalkyl enones 22-24, and their analogs [206,[215][216][217][218][219][220], and functionalized derivatives bearing sulfonyl [221] or alkynyl [222] groups. Notably, in most cases, the condensation reaction proceeded in a regioselective manner.…”

Regioselective reaction of 5,6-dialkyl-2-halopyridine-3,4-dicarbonitriles with ammonia

“…The halogen atom in 2-halopyridine-3-carbonitriles is activated by the neighboring cyano group, and it can be readily replaced under mild conditions, e.g., by nitrogen-containing nucleophiles [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Depending on the substrate and reagent nature, these transformations may be catalyzed by the reacting nucleophile [5,6] or other base such as potassium [7,8] or cesium carbonate [9,10], sodium hydrogen carbonate [11,12], triethylamine [13,14], ethyl(diisopropyl)amine [15,16], etc. Taking into account reduced nucleophilicity and high volatility of ammonia compared to primary and secondary amines, 2-aminopyridine-3-carbonitriles are synthesized under pressure [12,17,18] or microwave irradiation [19].…”