Pyrazolin-5-thiones

The reaction requires temperatures of 100-150° and all pyrazolinones of this type undergo it. The oxygen of 2-pyrazolin-5-ones can also be replaced by sulfur if phosphorus pentasulfide at about 130-150° is used (eq. 44).739-1343 This reaction is widely used for preparation of 2-pyrazolin-5-thiones. 

The reaction of 2-pyrazolin-5-ones with phosphorus pentasulfide forms 2-pyrazolin-5-thiones (eq. 44).759 990,1343 The reactants are usually heated at the temperature of boiling xylene. A second method used in the preparation of such compounds is the reaction of 5-chloro-pyrazoles with potassium hydrogen sulfide (eq. 88).977,990,1003... 

Michaelis and co-workers990 have prepared 3-methyl-l-phenyl-4-phenylazo-2-pyrazolin-5-thione by coupling of the corresponding pyrazolinthione with phenyldiazonium chloride. 

Benzoyl-3-methyl-l-phenyl-2-pyrazolin-5-thione has been prepared by Michaelis and co-workers977,990 by the reaction of sodium and potassium hydrogen sulfide with 4-benzoyl-5-chloro-3-methyl-l-phenyl-pyrazole. The thiono compound forms a methiodide and gives the characteristic reactions of both ketones and 2-pyrazolin-5-thiones. 

When the oxygen atom is replaced by a sulfur atom as in pyrazoline-5-thiones, the CH form (145a) never occurs, and the tautomerism implies only the SH (145b) and the NH (145c) forms (77BSB949). 

Pyrazoline-5-thione, 2,3-dimethyl-1 -phenyl- CNMR, 5, 194 (74JHC135) 3-Pyrazoline-5-thione, 1,2,4-trimethyl-PE, 5, 205 (78JA1275)... 

C NMR, 5, 193 Pyrazoline-5-thiones tautomerism, 5, 215 Pyrazoline-5-thiones, 1-aryl-reactions, 5, 102... 

Pyrazoline-5-thiones photoelectron spectroscopy, 5, 205 Pyrazolinium salts reduction, 5, 254 Pyrazolinium salts, 1,2-dimethyl-synthesis, 5, 276... 

Similar behavior was also observed for analogous 3-oxopyrazolidines 282 (X = O) and pyrazoline-3-thiones 282 (X = S) (Scheme 101). 

In variants of the above processes, the bifunctional reactivity of 4-(dialkylamino-methylene)pyrazolin-5-thiones (155) (Scheme 25) and oxazolin-5-thiones (157) (Equation (45)) with a-halocarboxylic acids (or esters) was exploited for the synthesis of thieno[2,3-c]pyrazoles (156)... 

More complex tautomeric equilibria have been observed for compound 21 involving the l,2,4,5-tetrazin-3-thione G. The equilibrium is strongly shifted toward the isoxazoline form A in solvents such as pyridine, acetone, dimethyl-sulfoxide (DMSO), and dimethylformamide (DMF), whereas the pyrazoline form D does not exceed 5-10% (Scheme 3) <2002CHE730>. The presence of the above tautomeric species has been demonstrated by NMR. 5-Hydroxy-3,3,5-trimethylisoxazolidine showed a similar behavior <2003CHE1257>. The presence of a CF3 group such as in 22 affects considerably the stmcture of these compounds, which exist only in the cyclic isoxazoline form <2000RCB1910>. 

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