Condensed pyrazoles

Although only a few condensed 5 6 or 5 5 aromatic pyrazole derivatives can be isolated from biological sources, the chemistry of condensed pyrazoles has received considerable interest. Condensed pyrazoles with an indene skeleton can be considered as purine analogues and, as such, are expected to have biological activity. The discovery of the xanthene oxidase inhibitory action of pyrazolo[3,4-fiT pyrimidine and the cAMP phos-phodiasterase inhibitory action of pyrazolo[l,5-a]pyrimidines has stimulated considerable interest in the synthesis of analogues of both ring systems. 

A review on the synthesis of pyrazoles and condensed pyrazoles covering the period of 1989-1998 was written <99JHC321>. 

K. Makino Synthesis of pyrazoles and condensed pyrazoles 1999JHC32I... 

A review has described the synthetic approaches, chemical properties, biological activities, and structure-activity relationships (SARs) of pyrazole nucleosides and condensed pyrazole nucleosides <2005NN1227>. Many of the references are pre-1996, and only selected post-1996 examples will be cited here. 

Besides AZ-aminoindazoles, there are N-amino derivatives of some other condensed pyrazole systems. Most were obtained on electrophilic amination of the corresponding heterocycles by HOSA [75JCS(P1 )31 ]. For instance, on amination of 5-methylpyrazolo[4,3-Z>]pyridine, 1- and 2-amino derivatives 27 and 28 are formed in yields of 42 and 40%, respectively. Similarly, amines 29 and 30 were obtained, whereas amination of pyr-azolo[3,4-/ ]pyridine (31) failed. 

V-Amino derivatives of condensed pyrazoles 26, 27, 29, and 31 are readily oxidized with LTA to the corresponding triazines [75JCS(P1)31, 75JCS(P1)1747]. 

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