Synthèse Et Isomérie De Thiométhylpyrazoles

Abstract

The shortly performed thermal conversion of 1, 2‐dimethylpyrazolin‐5‐thiones leads to 1‐methyl‐3‐methylthiopyrazoles. The isomerization of these compounds into mixtures of 3‐methylthio and 5‐methylthiopyrazoles is observed after several months at room temperature or more rapidly after prolonged heating. 1‐methyl‐3‐methylthio‐ and 5‐methylthiopyrazoles appear thus respectively as the kinetic and thermodynamic products of the reaction which proceeds at least mainly via an intermolecular mechanism. The thermal intermolecular conversion of 1‐phenyl‐2‐methylpyrazolin‐5‐thiones leads exclusively to 1‐phenyl‐5‐methylthiopyrazoles as described in the literature.

N-arylation of 3-alkoxypyrazoles, the case of the pyridines

“…28 More thorough studies of the tautomeric forms of some pyrazol-3-ones adopted in solution have also been reported. 29,30 As depicted in Scheme 3, further reactions were studied from 2-bromopyridine (2a) and the 3-ethoxypyrazoles 10a-k, previously reported 1,2,31 or prepared as described in the Experimental part. Few remarkable facts were noticed in this study.…”

Spectrométrie de Masse de Pyrazoline‐5‐Ones N1 Substituées. II. 2‐Pyrazoline‐5‐Ones A Structure Fixe et Pyrazoline‐5‐ones Tautomérisables.

“…Ces faits tendent P prouver l'existence en phase gazeuse de XXI sous forme CH. Ce resultat est conforme P celui attendu au dgpart des donnees concernant l'influence du milieu (25). En outre, le spectre infrarouge(")en phase vapeur de la substance prdsente une bande a 1740 cm-l, reprdsentative de l'isombre CH.…”

Tautomérie dans la Série des Pyrazolinones II. Influence Du Milieu Sur L'équilibre Prototropique Des Pyrazoline‐5‐Ones N1 Substituées

“…de ces compos6s phdnyl&s, notre etude se limite 11 la l-phEnyl-3-m&thyl-pyrazoline-5-one (11). Cette substance presente, en fait, un comportement semblable B celui de la 1,3-dim6thylpyrazoline-5-one (1). Dans le m6thano1, on observe une faible bande v(C=O) 5 1697 cm-' correspondant 3 l'isombre CH dont la teneur deterrninde par R.M.N.…”

“…La faible absorption aux environs de 240-260 nm du composd alkyl6 ( I X ) mantre 6galement que les isomeres CH et NH sont quantitativement peu importants. Les pourcentages approximatifs des diff6rents tautomeres de la 1 , 4 -d i m 6 t h y l p y r a z o l i n e -5 -o n e (Tableau 6) sont Bvalu6sSelOn la m6thode d6crite anterieurement(1).…”