Studies in the azole series. CIII. adamantyl and halogeno pyrazolin‐5‐ones

Abstract

Nine new pyrazolinones are described together with the crystal structure of one of them, namely 344-chloropyrazol-1 -yl)-4,4-dichloro-2-pyrazolin-5-one, 8, which has been solved. by X-ray crystallography. The molecule is planar since it lies on a mirror plane and packs first in chains through hydrogen bonds, then in sheets through strong CI-0 interactions. An NMR study in the solid state and in solution proves that the major tautomer is the 3-pyrazolin-5-one c.

Preparation and Chemistry of 3/5-Halogenopyrazoles

“…As depicted in Scheme , chlorination of pyrazole ( 15 ) does lead to 4-chloropyrazole ( 16 ) along with polymeric material from which was later identified the symmetrical compound 17 . More recently, additional chlorination of this trimer, followed by hydrolysis, was shown to lead to the trichlorinated dimeric derivative 18 . We also observed such side reactions in the course of chlorination trials with N -chlorosuccinimide .…”

“…41 More recently, additional chlorination of this trimer, followed by hydrolysis, was shown to lead to the trichlorinated dimeric derivative 18. 42 We also observed such side reactions in the course of chlorination trials with N-chlorosuccinimide. 43 Bromination of 4-methylpyrazole (19) with bromine was established, by 1 H NMR, to lead to the symmetrical trimer 20 44−46 related to compound 17.…”

The amphoteric role of nitrogen in the NX2 unit within crystals

“…Other weak interactions were hidden for clarity. The CSD codes are: (i) BEXNAV, 46 (ii) DESKER, 47 (iii) FUBXOQ, 48 (iv) KECRAN, 49 (v) NOPREP, 50 (vi) PICCIN, 51 (vii) PIMXUH 52 and (viii) PUYQIK. 53 Table S3 † shows the k-means cluster analysis, and Table S4 † lists the centroids of each group.…”