1,3-Diketones from Acid Chlorides and Ketones:  A Rapid and General One-Pot Synthesis of Pyrazoles

Abstract

[reaction: see text] 1,3-Diketones were synthesized directly from ketones and acid chlorides and were then converted in situ into pyrazoles by the addition of hydrazine. This method is extremely fast, general, and chemoselective, allowing for the synthesis of previously inaccessible pyrazoles and synthetically demanding pyrazole-containing fused rings.

Self‐Assembly in Helical Columnar Mesophases and Luminescence of Chiral 1H‐Pyrazoles

“…However, this reaction often gives low yields and extensive hydrolysis of the benzoate ester, and it is very sensitive to the storage conditions of NaH. For this reason, we prepared the pyrazoles described in this work by adapting a recently described one-pot procedure [20] to our polyalkoxy starting materials. The method uses a weaker base (lithium 1,1,1,3,3,3-hexamethyldisilazane or LiHMDS) to generate the enolate of the acetophenone, low temperatures, and acid chlorides, which are better electrophiles than esters.…”

A facile synthesis and charecterization of 2,5 disubstituted Pyrazolones

“…Colored crystals of 4-arylmethylene-2,4-dihydro-2,5-disubstituted-3H-pyrazol-3-one were separated, filtered, dried and recrystallized from benzene. At this stage, if no crystals separated, a small amount of water was added till slight turbidity appeared and the mixture was allowed to stand to get colored crystals of 4-arylmethylene-2,4-dihydro-2,5-disubstituted-3H-pyrazol-3-ones [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], filtered, dried and recrystallized from benzene.…”

Regioselective One‐Step Synthesis of Pyrazoles from Alkynes and N‐Tosylhydrazones: [3+2] Dipolar Cycloaddition/[1,5] Sigmatropic Rearrangement Cascade

“…[10] For these reasons, the development of new methodologies for the regioselective synthesis of polysubstituted pyrazoles continues to be an active area of research of high impact in fine chemistry. [11] The most popular approaches to the synthesis of trisubstituted pyrazoles consist of: 1) condensation of hydrazines with 1,3-dicarbonyl compounds or synthetic equivalents; [12] 2) [3+2] cycloadditions of diazo compounds or other N = Ncontaining dipoles with alkynes [13][14][15] or alkenes; [16] 3) transition-metal-catalyzed cross-coupling reactions. [17] Nevertheless, the efficient preparation of 3,4,5-trisubstituted pyrazoles in a regioselective manner is still a challenging task which involves several synthetic steps.…”