Efficient syntheses of approximately 70 simple substituted representatives of pyrazolo[3,4-Olpyridine 1 are reported from the following: ( a ) suitably substituted pyridines onto which a pyrazole ring is annelated, and (6) appropriately substituted pyrazoles onto which a pyridine ring is annelated. Selected examples of electrophilic, nucleophilic, and homolytic substitution reactions and group transformations are described, providing regiosynthetic paths to useful intermediate species. Some (26)). Our interest in synthesis and reactivity of the parent compound and its substitution products arises from promise shown as inhibitors of xanthine oxidases (27). A minor portion of our work has been reported in another study of purine analogues (28), and we have also described the synthesis of the parent system by rearrangement accompanying decarboxylation of pyrazolo[l,5-alpyrimidine carboxylic acids (29).This paper reports efficient syntheses of pyrazolo[3,4-blpyridines from (a) suitably substituted pyridines onto which a pyrazole ring is annelated, and (b) appropriately substituted pyrazoles onto which a pyridine ring is annelated. We present examples of electrophilic, nucleophilic, and homolytic substitution reactions and group transformations providing regiosynthetic paths to useful intermediate species. Aspects of substituent chemical shift influences in the 'H and 13C nr111. spectra are illustrated.
A general cyclization route to pyrazolo[1,5-a]pyrimidines from 3-aminopyrazole and 1,3-dicarbonyl compounds is applied to synthesis of the parent ring system. In nitration of this species the orientation of substitution is strongly reagent dependent. Mixed nitric and sulfuric acids yield the 3-nitro compound, whereas nitric acid in acetic anhydride yields the 6-nitro compound. Brominations yield 3-bromo and 3,6-dibromo species.The majority reacting species in the strongly acidic medium is identified as the 1-protonated entity by conjoint use of approximate molecular orbital calculations and the variation of coupling constant patterns accompanying protonation. The molecular orbital calculations predict successive 3- and 6-substitution by electrophiles in pyrazolo[l,5-a]pyrimidine and its conjugate acid, and an addition–elimination sequence is proposed to account for the observed 6-nitration.
188ChemInform Abstract With a view to their potential activities as inhibitors of xanthine oxidases, approximately 70 simple substituted representatives of pyrazolo (3,4-b)pyridine are prepared by various methods; the main strategies involve anellation of a pyrazole ring onto a suitable substituted pyridine such as (I) to give the title compounds (IV) and anellation of a pyridine ring onto a pyrazole such as (VII) to give the pyrazolopyridines (V) or (IX).
Das durch Decarboxylieren der Säure (Ia) bei 170°C erhältliche Pyrimidin (Ib) wird mit 1,1,3,3‐Tetramethoxypropan zu der Titelverbindung (II) kondensiert.
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