3- -2-pyrazoline

ELALffiRETARDANTS - PHOSPHORUS FLALffi RETARDANTS] (Vol 10) l-Aryl-2-pyrazolin-5-ones... 

Pyrazolones. The 0x0 derivatives of pyrazolines, known as pyrazolones, are best classified as follows 5-pyrazolone, also called 2-pyrazolin-5-one [137-44-0] (36) 4-pyrazolone, also called 2-pyrazolin-4-one [27662-65-3] (37) and 3-pyrazolone, also called 3-pyrazolin-5-one [137-45-1] (38). Within each class of pyrazolones many tautomeric forms are possible for simplicity only one form is shown. 

A -Pyrazolines and A -isoxazolines (302 Z = NH, O) are cyclic hydrazones and oximes, respectively. 2-Pyrazolines are quaternized at the 2-position (306 307) (64AHC(. ll). 1,3,4-Oxadiazolines (e.g. 308) are very easily ring-opened (66AHCi7 183). 

Methyl-l -phenyl-2-pyrazolin-5 -one CDCI3 -186.4 -54.5 C- N and H- coupling constants 77JCS P2)1024 ... 

Pyrazolones show a great variety of reactions with carbonyl compounds (B-76MI40402). For instance, antipyrine is 4-hydroxymethylated by formaldehyde and it also undergoes the Mannich reaction. Tautomerizable 2-pyrazolin-5-ones react with aldehydes to yield compound (324) and with acetone to form 4-isopropylidene derivatives or dimers (Scheme 8 Section 4.02.1.4.10). 

A-Oxidation with peracids (Section 4.04.2.1.3) and the transformation of pyrazoles into 4,4-dihalogeno-2-pyrazolin-5-ones (Section 4.04.2.1.4(v)) have already been discussed. Transformation of non-aromatic 2-pyrazolin-5-ones into the 4-oxo derivatives will be examined in Section 4.04.2.2.l(ii). 

Pyrazolin-5-ones with an exocyclic double bond at the 4-position (369 X = CMe2> react as heterodienes towards alkyl vinyl ethers (77G91). The kinetics of this Diels-Alder reaction giving pyrazolopyrans (370) have been studied. 

LiAlH4 did not reduce 2-pyrazolin-5-ones (70BSF1974). See also formulae (365) and (366). (68M2157). 

Pyrazolines substituted at position 4 or 5 with hydroxy or amino groups readily eliminate a molecule of water or amine yielding pyrazoles. The 4-substituted derivatives are relatively more stable than the 5-substituted ones, because for the last group the lone pair at N-1 assists the elimination (407) -> (408) -> (409). The sulfonyl group at position 1 is also easily eliminated and this property is taken advantage of in Dorn s elegant synthesis of 3-aminopyrazole (Section 4.04.3.3.1). 

A -Pyrazolines such as (410) are oxidized by iodine, mercury(II) acetate and trityl chloride to pyrazolium salts (411), and compound (410) even reduces silver nitrate to Ag° (69JOU1480). Electrochemical oxidation of l,3,5-triaryl-2-pyrazolines has been studied in detail (74BSF768, 79CHE115). They Undergo oxidative dimerization and subsequent transformation into the pyrazole derivative (412). 

The fact that an OH or OR group in position 3 or 5 enhances the reactivity of the pyrazolic 4-position towards electrophiles has already been discussed (Section 4.04.2.1.3). Likewise, the non-aromatic reactivity of 2-pyrazolin-5-ones has been examined in Section 4.04.2.2.1(ii). 

Muzolimine (710), a 1-substituted 2-pyrazolin-5-one derivative, is a highly active diuretic, differing from the structures of other diuretics since it contains neither a sulfonamide nor a carboxyl group. It has a saluretic effect similar to furosemide and acts in the proximal tubule and in the medullary portion of the ascending limb of the loop of Henle. Pharmacokinetic studies in dogs, healthy volunteers and in patients with renal insufficiency show that the compound is readily absorbed after oral administration (B-80MI40406). 

Phenidone, l-phenyl-3-pyrazolidone (738) (B-76M140404), has been used as a nonstaining, high contrast photographic developer. New optical brighteners containing 2-pyrazolines (739) and pyrazoles (740) have been synthesized recently and their properties and applications reviewed (75AG(E)66s). 

H NMR, 5, 188 (70BSF3466, 67MI40402) 2-Pyrazoline, 5-methoxycarbonyl-4,5-diphenyl-X-ray, 5, 191 (76BSB545)... 

Pyrazolin-5-one, 3-methyl- H NMR, 5, 187 (B-73NMR165) 2-Pyrazolin-5-one, 3-methyl-1 -phenyl- H NMR, 5, 187 (B-73NMR165)... 

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