Pyrazoles pyrazole-fused ring systems

Many methods for the preparation of pyrazole-fused ring systems were published. The different structural types are listed in the table below. 

Pyrazole-fused ring systems Pyrazole-fused ring types... 

Pyrazoles, Indazoles, and their Derivatives as Starting Materials for the Syntheses of Fused Ring Systems... 

Fused ring systems containing a pyrazole unit can be prepared either from the heterocyclic moiety by formation of a pyrazole ring or from the reaction between a pyrazole derivative and a suitably functionalized reagent. The ring systems thus obtained are discussed in detail in other chapters (Chapters 4.05, 4.35, 4.36) but it is of interest to discuss here those methods which start from a pyrazole derivative as the reactions involved can be considered as examples of the reactivity of pyrazoles. The most widely studied fused ring systems are the [5.6] systems and the examples described in this section will be chosen from this group and, occasionally, from [5.5] and [5.7] systems. 

Table 34 Synthesis of Fused Ring Systems from Pyrazoles and Indazoles...

Simple 4//-pyrazoles break down in mass spectroscopy by loss of one 4-substituent to give an aromatic ion, followed by elimination of nitrogen and fragmentation of the remaining carbon skeleton.15,66,67 For the fused-ring systems 29, nitrogen loss is not apparent,49,65 and in the case of structures 71 and 72, accurate mass measurements have shown that initial loss of 28 units is due to C2H4 and not Nj.46... 

PYRAZOLES, INDAZOLES, AND THEIR DERIVATIVES AS STARTING MATERIALS FOR THE SYNTHESES OF FUSED RING SYSTEMS... 

Compounds 39 and 40, in which a pyrazole ring is fused to a pyrido[2,3-2,]pyrazinc, are produced as a 3 2 mixture by reaction of pyridine-2,3-diamine with 3-methyl-l-phenylpyrazoline-4,5-dione (Equation 9) <1999T8475>, and the synthesis of compound 41 (Scheme 11) exemplifies a different approach to the same ring system <1997JCM318, 1997JRM2026>. 

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