Pyrazole compounds

The syn-anti conformational problem of a- and /3-pyrazofurins (756 one of the rare naturally occurring pyrazole compounds, see Section 4.04.4.4.3), which involves a rotation around a pyrazolic sp carbon atom and a sugar sp carbon atom, has been studied theoretically using the PCILO method (81MI40403). In agreement with the experimental observations, the /3 anomer is energetically more favourable than the a anomer, the preferred conformations being anti and syn, respectively. 

The complex OsH(pz)(CO)(Hpz)(P Pr3)2 is a useful starting material to prepare new pyrazole compounds. Reaction with HBF4-OEt2 leads to the cation... 

Fused pyrazole compounds have been prepared from A-alkyl substituted pyrazoles. For example, a palladium-catalyzed/norbornene-mediated sequential coupling reaction involving an aromatic sp2 C-H functionalization as the key step has been described, in which an alkyl-aryl bond and an aryl-heteroaryl bond were formed in one pot <060L2043>. A variety of highly substituted six-membered annulated pyrazoles 59 were synthesized in a one-step process in moderate yields from IV-bromoalkyl pyrazoles 57 and aryl iodides 58. 

Synthesis of biologically active epoxides were reported by Le Blanc et al. and were synthesized initially as a route into the pyrazole compounds shown in Sect. 3.2.1a Scheme 48 [80]. Scheme 35 shows the synthesis of two of the most active epoxides 139a and 139b. They were formed from the reaction of chal-cones (140a and 140b, respectively) by reaction with H2O2 and K2CO3 in MeOH... 

Wiley RH, BehrLC, Fusco T, Jarboe CH (eds) (2008) Chemistry of pyrazole compounds. In Chemistry of heterocyclic Compounds pyrazoles, pyrazolines, pyrazolidines, indazoles and condensed rings. Wiley, New York... 

In 1889, Buchner (18) reported the formation of the insoluble silver(I) pyr-azolate [Ag(pz)] , la, which he simply denoted as a silver salt . The oligo-metric or polymeric nature of this species was not clarified until 1994, although it was always referred to as being a polynuclear pyrazolate compound (6). A similar structure was claimed for [Cu(pz)], 2, on the basis of IR evidences (6, 19). 

Some pyrazolate complexes were found to possess high catalytic activity for various hydrogen-transfer processes and to be of considerable value in synthesis. The heterodinuclear complexes [(CO)(H)(PPh,)2Ru( -pz)(/x-Cl)M(diolefin)] (M = Rh or Ir diolefin = cod or tfbb) catalyze the hydrogen transfer from isopropanol to cyclohexanone (101). The heterodinuclear complexes were shown to be more active catalysts than the mononuclear pyrazole compounds [Ru(H)(Cl)(Hpz)(PPh,)2] and [M(H)(Cl)(Hpz)(diolefin)] (101). 

After the early reviews in 19712 and 19723 on poly(pyrazolyl)borate chemistry and pyrazole-derived ligands, and the boron pyrazole compounds chemistry described in 1986,4 Trofimenko reported in 1986s and in 19936 a summary on the coordination chemistry of poly(pyrazolyl)-borates. In 1999 Trofimenko described the coordination chemistry of scorpionate ligands in a book.7... 

Likewise, the fused-ring triazoline adducts 112, obtained from 1-methyl-1,2,4-triazolium-4-(acyl)imides and propiolic ester, undergo rupture at the N—N or C—N bond to yield triazole or pyrazole compounds (Scheme 37) (76CPB2568). 

Diels and coworkers have shown that, when n-arafemo-hexulose phenyl-osazone is oxidized with oxygen (or air) in an alkaline medium, a dehydro-osazone is obtained which possesses two hydrogen atoms fewer than the parent osazone. On acetylation, the compound gives a triacetate, and its hydrazine residues could not be removed with p-nitrobenzaldehyde, suggesting their involvement in ring formation. The authors supported this view by the findings that dehydro-osazones cannot be obtained from methylphenylosazones or from the Diels anhydro-osazone (which, at that time, was believed to be a pyrazole compound). 

Ring contraction of (53) under basic conditions has been reported to result in the thiazolo[3,2-Z ]pyrazole compound (54) (Equation (3)) <88S729>. 

These pyrazole compounds show a strong resemblance to the nitrogen-bonded p3frazoylbor-ate complexes. References to a number of these complexes are given in Sections 52.2 and 52.4 an example not previously mentioned is the complex [PtMe(CNBu ) HB(pz)3 ]. The Pt— distances are in the range 2.0-2.1 A. In this complex the ligand adopts bidentate coordination,but many complexes are known where tridentate coordination is observed. 

Tautomerism and Isomerism Syntheses of the Pyrazole Ring General Reactions of Pyrazole Compounds Chemistry of Pyrazole Compounds Introduction [to Reduced Pyrazoles] Pyrazoline Syntheses Chemistry of the Pyrazolines Pyrazolidine Chemistry... 

Fox SL. Potentiation of anticoagulants caused by pyrazole compounds. JAMA (1964) 188, 320-1. 

Idemitsu also concentrated their efforts on new acids, with emphasis on those in which the alkylsulfonyl substituent at the 4 position was joined into a ring at the 3-postion (typical Idemitsu types 57-61 are shown in Fig. 4.3.10) [55]. Although they received a patent for compounds of this type with 2-chloro substituent (e.g., 59) they were also forced to switch to more complicated substituted heteroaromatic systems after the publication of interfering patents from Zeneca [33], or to pyrazoles [56]. They now appear to have a pyrazole compound (generic structure 61, Fig. 4.3.10) in development for use in corn, based on recently published mixture patents [57]. 

SOLID-PHASE SYNTHESIS OF RELATED PYRAZOLE COMPOUNDS AND 1,3,4-TRIAZOLES VIA A DITHIOCARBAZATE LINKER... 

SOLID-PHASE SYNTHESIS OF RELATED PYRAZOLE COMPOUNDS... 

Mechanistic studies have been carried out on the formation of diazines by ring expansion of azolyl-1-methyl radicals formed upon FVP of 1-aryloxy-methylpyrazoles and 1-aryloxymethylimidazoles at 700 °C (2015UP1). The pyrazole compound 368 gives exclusively pyrimidine, while the imidazole compound 369 gives both pyrazine and pyrimidine in the ratio shown in Scheme 74 (2015UP1). The effect of methyl substituents is demonstrated by the results for the imidazoles 370 and 371 (Scheme 74). 

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