An NMR and Computational Study of Azolo[a]pyrimidines with Special Emphasis on Pyrazolo[1,5‐a]pyrimidines

Abstract

The reaction of 3(5)‐amino‐5(3)‐hydrazinopyrazole, a bifunctional compound, with 3‐oxo‐3‐phenylpropanenitrile and two of its p‐substituted derivatives affords 2,5‐diaryl‐7‐aminopyrazolo[1,5‐a]pyrimidines. A mechanism for this unexpected reaction involving the formation of hydrazine is proposed. The position of the aryl substituents on the bicyclic ring has been established by the combined use of NMR and DFT calculations. Moreover, the chemical shifts have been calculated, and some general rules have been withdrawn.

Molecular docking design and one-pot expeditious synthesis of novel 2,5-diarylpyrazolo[1,5-a]pyrimidin-7-amines as anti-inflammatory agents

“…In 13 C NMR, two signals at δ 84.7 ppm and δ 91.5 ppm were observed corresponding to 6-C and 3-C. Signal for 7-C appeared at δ 148.45 of pyrazolo[1,5-a]pyrimidine nucleus thus confirming the formation of 2-phenyl-5-p-tolylpyrazolo[1,5-a]pyrimidin-7-amine isomer (4a). The spectral data is in conformity with our recent report where in regioselective synthesis of 7-aminopyrazolo[1,5-a]pyrimidines have been achieved by the reaction of 3(5)-amino5(3)-hydrazinopyrazole with 3-oxo-3-phenylpropanonitrile (2a) and the position of substituents on pyrazolopyrimidine ring has been established by the combined use of NMR (HMBC & HMQC) and DFT calculations[7].…”

Some important inhibitors and mechanisms of rheumatoid arthritis

“…Pyrazole structure and the fused pyrazole six‐membered ring structure are the main skeletal characteristics of different types of non‐steroidal anti‐inflammatory drugs (NSAIDs) (Aggarwal, Kumar, et al, 2015). Pyrazole‐(Dixon et al, 2006; Walker & Farrow, 2007)‐pyrimidine system was similar in nature to purine and represents an important structural type that has anti‐inflammatory activity and selectively inhibits COX‐2 activity (Kosugi et al, 2012).…”

Computational1H and13C NMR in structural and stereochemical studies

“…A number of further illustrative examples deals with azoles, benzoazoles, phosphazoles, [ 215–217 ] imidazoles, [ 218 ] bipyridines, [ 219 ] pyrimidines, [ 220 ] triazines, [ 221 ] indazoles, [ 222,223 ] pyrazolopyrimidines, [ 224 ] carbazoles, [ 225,226 ] and many other heterocycles. [ 227–230 ] Those and further examples are not presented here, insofar as they are thoroughly discussed in the reviews cited in the Introduction.…”