Researches on pyrazoles

Alkyl and aryl pyrazoles are acylated at position 4 by the chloroanhydrides and anhydrides of the lowest fatty and aromatic acids in the presence of catalytic amounts of sulfuric acid. Reaction is readily effected because it is the neutral pyrazole molecule which is being acylated. In individual cases 1, 3, 5-trimethylpyrazole can be alkylated at position 4 by the Friedel-Crafts reaction.For Part IL see [6].     

Researches on pyrazoles

The existence of an ortho effect in 1-phenyl-5-substituted pyrazoles is proved by analyzing the UV and fluorescent spectra of a number of 1-phenylpyrazoles. The effect leads to destruction of the coplanarity of the phenyl and pyrazole rings.For Part III see [19].     

Researches on pyrazoles

The pyrazole ring is opened by sodamide to give the corresponding -iminonitriles.For Part L see [11].     

Researches on pyrazoles LII. IR Spectra and lactim-lactam tautomerism of pyrazolopyridones

The IR spectra of the previously synthesized pyrazolo[3,4-b]- and pyrazolo [4, 5-b] pyridones are investigated. From analysis of the IR spectra of the pyrazolopyridones themselves, and of complexes with heavy metal salts, as well as of some model compounds, conclusions are drawn regarding their lactam structure.     

Researches on pyrazoles LII. IR Spectra and lactim-lactam tautomerism of pyrazolopyridones

The IR spectra of the previously synthesized pyrazolo[3,4-b]- and pyrazolo [4, 5-b] pyridones are investigated. From analysis of the IR spectra of the pyrazolopyridones themselves, and of complexes with heavy metal salts, as well as of some model compounds, conclusions are drawn regarding their lactam structure.For Part LI see [20].     

Studies on pyrazoles

A number of -amino acids of the pyrazole series have been synthesized by the direct Rodionov reaction and have been characterized by their UV spectra, electrophoretic mobility, and paper chromatography.For part LVIII, see [1].     

Studies on pyrazoles

A new method has been developed for the synthesis of N-vinylpyrazoles from pyrazoles not substituted at the nitrogen atom. This synthesis is accomplished by the action of vinyl acetate and is catalyzed by mercuric sulfate.For part LIX, see [1].     

Studies on pyrazoles

The possibility of the separation into optical antipodes of racemic amino acids of the pyrazole series has been investigated. The trans configuration of the acrylic acids obtained as by-products in the synthesis of -amino acids of the pyrazole series by the Rodionov reaction has been shown by PMR and IR spectroscopy. The IR spectra of a series of amino acids are discussed.For part LXII, see [1].     

Synthesis of pyrazoles and condensed pyrazoles

This review introduces the synthesis of various pyrazoles reported by us and some other research groups during 1989–1998. Some of papers in this review deal with the development of potent pyrazoles or with the synthesis of potential pyrazoles aiming at agrochemicals and/or drugs.     

Research on pyrazoles. XLVII. Synthesis of pyrazoles with long-chain alkyl substituents

A number of alkylpyrazoles with long alkyl side chains are synthesized.In investigating the pharmacological activity of a number of pyrazole derivatives [2, 3], it was found that alkylpyrazoles have an appreciable effect on the central nervous system. To investigate this effect in greater detail, a number of alkylpyrazoles with long alkyl side chains at positions 1 and 3 were synthesized.For part XLVI see [1].     

5-Fluoro-substituted pyrazoles

A preparative method was developed for the synthesis of 5-fluoro-substituted pyrazoles by the reaction of fluoroolefins with substituted hydrazines in the presence of triethylamine. The fluorine atom at the C₅ position of the pyrazoles obtained is readily substituted by O-, N-, and S-nucleophiles with the formation of 5-alkoxy-, amino-, mercapto-substituted fluoroalkylpyrazoles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2583–2589, November, 1990.     

Synthesis of pyrazoles

This review summarizes the synthesis of various pyrazoles reported by us and some other research groups in 1981–1989.     

A study of pyrazoles

The reactivity of pyrazolo[2, 3-a]pyridine in electrophilic substitution reactions has been studied. It has been shown that electrophilic attack is directed to position 3 (equivalent to position 4 of the pyrazole nucleus). The position of entry of the substituents was shown by chemical methods and was confirmed by a study of PMR spectra.     

An investigation of pyrazoles

Methods have been developed for obtaining vinyl derivatives of various pyrazoles containing vinyl groups in positions 1 and 4 from the corresponding hydroxyethyl derivatives.For communication LVT, see [1].     

Synthesis of tetra-substituted pyrazoles

A set of highly substituted pyrazoles bearing different functional groups on the pyrazole core was developed. Employing a suitable protecting group strategy we could regioselectively introduce various substituents in position 1, 3 and 4 of the pyrazole. This enabled the synthesis of various derivatives of a pyrazole–biscarboxamide with insecticidal activity. During the optimization process we focused on the precise exchange of carboxamide as well as other functional groups based on the concept of bioisosterism.     

Columnar metallomesogens derived from unsymmetrical pyrazoles

The synthesis and mesomorphism for two series of unsymmetrical pyrazoles and their nickel(II) complexes were described. This is the first example of nickel complexes exhibiting columnar phase. The derivatives with two alkoxy chains exhibited smectic A or smectic C phases; however, all derivatives with four alkoxy chains formed hexagonal columnar phases. In contrast, all nickel(II) complexes 1a formed hexagonal columnar phases. The crystal and molecular structures of 1-(4-propyloxyphenyl)-2-(3-(4-propyloxyphenyl)-1H-pyrazol-5-yl)ethanone were determined, and it crystallizes in the triclinic space group P-1. The overall molecular shape is considered as rod-shaped. The pyrazole and one phenyl ring were coplanar, however, they were not coplanar with other phenyl ring by a dihedral angle of ca. 66.2°. A dimeric structure formed by an intermolecular H-bond (2.11 Å) and a weak π-π interaction (3.51 Å) was observed, which was probably attributed to the formation of the mesophase. The XRD experiments confirmed their structures of the mesophases.     

Calamitic metallomesogens derived from unsymmetric pyrazoles

Three series of copper(II) complexes 1a-1c derived from unsymmetric pyrazoles 2a-2c were prepared and their mesomorphic properties investigated. The mesomorphic behavior of compounds was studied by differential scanning calorimetry, polarizing optical microscopy, and powder X-ray diffractometry. The crystal and molecular structures of mesogenic copper complex (2a; n=10) of 3-[4-decyloxyphenyl]-1H-pyrazole were determined by means of X-ray structural analysis. It crystallizes in the triclinic space group P-1, with a=4.0890(1) Å, b=18.0167(2) Å, c=25.5015(5) Å, and Z=2. The geometry at copper center was not perfectly square planar. A weak intermolecular H-bond (d=2.36 Å) between Cl1 and H2 atoms and π-π interaction (ca. 3.45-3.55 Å) was also observed. All their precursors 2a-2c were not mesogenic. In contrast, copper complexes 1a formed nematic or smectic C phases and complexes 1b-1c formed crystalline phases. Powder X-ray diffraction experiments confirmed the presence of SmC phase.     

Hydroxy- and alkoxymethylation of polyfluoroalkyl pyrazoles

A synthetic route to 1-hydroxy- and 1-alkoxymethyl-3-polyfluoroalkylpyrazoles via regioselective N-hydroxy- and alkoxymethylation of N-unsubstituted pyrazoles with paraformaldehyde has been proposed. The alkoxyalkylation of polyfluoroalkylpyrazoles proceeds in aqueous-alcohol medium, whereas hydroxymethylation requires anhydrous conditions.     

Researches on alkoxysilanes

Reaction of 1,2-, 1,3-, 1,4-, 1,5-, and 1,6-glycols, and of catechol, pentaerythritol, and glycerol with dialkyldichlorosilanes (in the presence of tertiary amines) dialkyldialkoxysilanes, or polydialkylsiloxanes gives 30 ethers of dialkylsilanediols containing 5, 6, 7, 8, 9, and 10-membered rings (16 being new). Among them are 8-membered ring ethers containing along with Si, O, and C, N or S, and 6-membered ring ethers containing NH₂, NO₂, and OH groups. 2-Sila -1,3-dioxolanes are obtained only when formation of the 1,3,6,8-tetraoxa-2, 7-disilacyclodecane ring is hindered or prevented by the presence of one or two substituents on each carbon atom with two substituents on the silicon. 2, 2-Dialkyl-1, 3-dioxa-2-silacyclanes, which contain 8 and 9-membered rings, can be obtained only by thermal depolymerization of originally formed polymeric ethers of the type [-O(CH₂)_nOSiR₂-]_m. Many of the monomeric cyclic ethers prepared dimerize or polymerize on keeping.For Part XVI see [1].     

Researches on imidazoles

Reaction of 1,2-dialkylbenzimidazoles with -halogenoketones followed by cyclization of the 1,2-dialkyl-3-ß-ketoalkyl(aralkyl)-benzimidazolinium halides in aqueous solution, in the presence of bases, leads to the synthesis of a number of derivatives of a new aromatic tricyclic system, 4H-pyrrolo[1,2-a]benzimidazole.For Part XXXII see [8].