Formation of Pyrazolines From Unsymmetrically Substituted Dibenzalacetones

Abstract

The purpose of this work was to extend our study of the action of phenylhydrazine on a ,/3-unsaturated ketones. In previous experiments (1) it was found possible in some instances to isolate the phenylhydrazones assumed by Auwers and co-workers (2) to be the first products in this reaction, but in many cases these compounds rearranged immediately to the isomeric pyrazolines. Straus (3) claimed that the ease of rearrangement will depend on the presence of substituents in the ketone and hydrazine residues. He stated that if one of the latter contains halogen or the nitro radical, closure of the pyrazoline ring will occur readily, while if both are substituted the hydrazone will be stable. It was desired to test these possibilities further.To decide whether this rearrangement had occurred, in previous work a number of methods have been studied. Auwers and Voss (4) found that the color test for pyrazolines proposed by Knorr (5), in which a drop of solution of ferric chloride, chromic acid, nitrous acid, or similar oxidizing agent is added to a concentrated sulfuric acid solution of the suspected compound, to give a blue-violet color, is not satisfactory. A trace of pyrazoline will give a positive reaction, and the fact that acids are the reagents which most readily bring about the rearrangement of these hydrazones1 raises the question whether some pyrazoline is formed when the reagent is applied. When the compound in question can be reduced by sodium amalgam (6) to give aniline as one product, it is regarded as a hydrazone.2 This can usually be rearranged by boiling acetic acid.3 Products

Synthesis of hydroxylated 3,5-diaryl-2-pyrazolines by the reaction of hydroxychalcones with hydrazines

“…Formation of 2-pyrazolines by the reaction of α,β-unsaturated ketones and hydrazines may take place under various reaction conditions using ethanol, 18 acetic acid [8][9][10]16,21,[25][26][27] or pyridine 28,29 as solvent. After some preliminary experiments, acetic acid was found to be a convenient solvent in our present case.…”

Synthesis of carboxylic acid derivatives of 2-pyrazolines

“…A mixture of the appropriate chalcone (13,(16)(17)(18)(20)(21)(22)10.0 mmoles), (2-carboxyphenyl)-hydrazine (30.0 mmoles) and acetic acid (60 mL) was refluxed for 5 h, then poured onto crushed ice. The oily precipitate was extracted with chloroform.…”

“…A mixture of chalcone (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)10.0 mmoles), (4-carboxyphenyl)hydrazine (30.0 mmoles) and acetic acid (50 mL) was heated at reflux for 7 h, then pured onto crushed ice. The precipitate was separated by filtration, washed with water and crystallized from methanol to afford 1-(4-carboxyphenyl)-2-pyrazolines 31-41 (Scheme 2).…”

Synthesis, Characterization and In-Silico Analysis of New 2-Pyrazolines

“…Pyrazolines are nitrogen containing five membered heterocyclic compounds [1] having wide range of biological activities such as cytotoxic [2], anti-platelet, anti-microbial [3,4], anti-tubercular [5], anti-inflammatory [5][6][7], anti-amoebic [8], hypotensive [9], antidepressant [10], antiviral [11], anti-cancer [12], anti-proliferative [13], anthelmintics [14], antioxidant [5], analgesic [15] and herbicidal activity [16]. The stability and biological activity motivated the researcher to synthesise and study more pyrazoline derivatives [4,16].…”