Über Pyrazoline

Preparation and Thermal Decomposition of Selected Pyrazolines.

“…The method used to establish the structure of the pyrazoline involved bromine oxidation to pyrazoles of known structure. shown by the non-conju-(XII) (9).…”

Aerobic aromatization of 1,3,5-triarylpyrazolines in open air and without catalyst

“…One of the most common routes to these compounds involves oxidative aromatization of the corresponding pyrazolines (4,5-dihydropyrazoles), since these are readily obtained by reaction of a chalcone with a hydrazine derivative. 10 Reagents used for this aromatization are diverse and have included manganese dioxide, 5 lead tetraacetate, 11 mercury oxide, 12 potassium permanganate, 13 various nitrates, [14][15][16] 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 17 hypervalent iodine reagents, 18 calcium hypochlorite, 19 Nbromosuccinimide, 20 iodic acid, 21 trichloroisocyanuric acid, 22 a 1,3,4-triazole-3,5-dione, 23 hydrogen peroxide/NaI or oxalic acid/NaI, 24 and a DABCO-Br 2 complex. 25 As a more unusual reagent, human hemoglobin in the presence of hydrogen peroxide has also been used.…”

Mild and efficient oxidation of 2-pyrazolines and isoxazolines by trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane–NH4Cl–HOAc in water–MeCN

“…Isoxazoles and 2-pyrazoles can be easily obtained by oxidation of isoxazolines [12][13][14][15][16][17] and 2-pyrazolines [18], respectively. Several methods have been reported for oxidation of isoxazolines and 2-pyrazolines including Pd-C-acetic acid [19], carbon-activated oxygen [20], cobalt soap of fatty acids [21] [23], manganese dioxide [24], potassium permanganate [24,25], silver nitrate [26], iodobenzene diacetate [27], zirconium nitrate [28], nickel peroxide [29], chromite [16], N-bromosuccinimide (NBS) [30], manganese triacetate [31], sodium bicarbonate-dimethylformamide [32], 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) [33], sodium carbonate-methanol [10], and tetrakis pyridine nickel(II) dichromate [34]. However, many of these methods have such disadvantages as long reaction times, low yields, and toxicity because of the elements present in the reagents used.…”