With polymeric pyrazoles

In these types of 1,3-dipolar cycloaddition only one of two possible isomers is obtained and the pyrazole functions have different orientations by the two methods. Another classical synthesis of pyrazoles (Section 4.04.3.2.l(ii)), the reaction between hydrazines and )3-diketones, has been used with success to prepare high molecular weight polypyrazoles (Scheme 65) (81MI40400). A-Arylation (Section 4.04.2.1.3(ix)) of 4,4 -dipyrazolyl with 1,4-diiodobenzene also yields polymeric pyrazoles (69RRC1263). 

Reactions of copper metal shot with molten pyrazole or substituted pyrazoles in the presence of dioxygen were successfully employed by Ehlert et al. (35— 37) in the synthesis of binary copper(II) pyrazolates of the general formula [Cu(pz )2] (Hpz = Hpz, 4-ClpzH, 4-BrpzH, or 4-MepzH). The complex [Cu(pz)2] , 15, was obtained in 79% yield as a bright green powder when the reaction mixture was heated at 110°C in the presence of air (35). The polymeric nature of 15 was ascertained by an X-ray crystal structure analysis. The Cu atoms have a D2 distorted tetrahedral coordination geometry with Cu—N = 1.957(2) A and N—Cu—N = 94.3(1)-139.5(1)°. In an earlier paper by Vos and Groeneveld (38), reactions of copper(II) salts with Hpz in aqueous base were reported to yield a black material of composition [Cu(pz)2] . The latter reactions were checked by Ehlert et al. (35) who attributed the composition [Cu2(pz)3(OH)] to the black material, rather than [Cu(pz)2] . 

Polymeric compounds are formed from 1,3,5-benzene tricarboxylate and zinc with 2,2 -bipyridyl, phenanthroline, or a pyridyl-2-(l-methyl-lH-pyrazol-3-yl) derivative. A number of compounds were characterized with varying ligand protonation and some, such as [ZnL(pyridine-2-(l-methyl-4-nitro-lH-pyrazol-3-yl))(H20)], containing single-stranded coordinative chains.383... 

The 2,3-dioxo-6-thioxo-2,3,5,6-tetrahydro-l/7-imidazo[l,2-A]pyrazole 393 and 5,6-dioxo-2,3-dihydro-l//-imidazo[l,2- ]-imidazole 395 were synthesized by condensation of the respective 5-amino-3-thioxo-2,3-dihydro-pyrazole 392 and 2-aminoimidazoline 394 compounds with either oxalyl dichloride or diethyl oxalate in moderate to poor yields (Equations 178 and 179) <1995JPR472, 2002EJM845>. These cyclizations can suffer from various side reactions such as expulsion of CO, polymerization, or formation of open-chain products. To solve these problems, reagents such as oxalic acid bis-imidoyl- and bis-hydrazoylchlorides 397 and 400 as well as 2,3-dichloroquinoxalines 403... 

Acetylenecarboxylic esters, reactions with nitrogen-containing heterocycles, 23, 263 Acetylenic derivatives of pyrazoles, synthesis and properties of, 82, 1 Acetylenic esters, synthesis of heterocycles through nucleophilic additions to, 19,297 Acid-catalyzed polymerization of pyrroles and indoles, 2, 287... 

Several d and / transition metals have been found to yield polymeric complexes with pyrazoles 14, 178). Reactions of these polymers with HFA produce monomeric species, HFA adding to the free nitrogen atom and the metal. Substitution of one carbon atom adjacent to nitrogen also results in degradation of the polymers. However, no reaction has been found when both a carbon atoms are sterically hindered 14). 

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