L//-3-Pyrazoline

A simple preparative route to the previously unknown lff-3-pyrazolines via azomethine lmines was developed. Olefins of the type r cH=CHR2 react with hexafluoroacetone azine to give azomethine imines, which undergo a sequence of prototropic shifts to form l//-3-pyrazolines [196, 202]. On heating, the latter are transformed into 3-trifluoromethylpyrazoles [196, 206] and, on treatment with bases, into 1,2,5,6-tetrahydropynmidines [206] (equation 45)... 

Based on this concept, a preparatively simple route to the previously unknown l//-3-pyrazolines was developed. Olefins of type RCH=CHR and hexafluoroacetone azine react to give azomethine imines, which subsequently are transformed in a series of prototropic shifts to give 1//-3-pyrazolines [75JCS(P1)538 79T389]. The latter on heating with AIBN undergo fluoroform elimination with heteroaromatization to yield trifluor-omethyl-substituted pyrazoles [82JFC(I9)437] (Scheme 63). 

Using hexafluoroacetone azine in reactions with olefins affords 5,5-bis(tri-fluoromethyl)-l//-3-pyrazolines 25, whose thermolysis yields 3-trifluoro-methylpyr-azoles 26 (82JFC( 19)437) (Scheme 25). 

Two syntheses of the rare l//-3-pyrazoline ring system have been reported/ and both rely on the ability of azines to act as 1,3-dipolar species in [3 + 2] cycloaddition reactions (Scheme 111). Certain annulated pyridazines are con-... 

PyraZolines. l,3-Diphenyl-2-pyia2olines (7) (Table 2) aie obtainable from appiopiiately substituted phenyUiydiazines by the Knoii reaction with either P-chloro- or P-dimethylaminopropiophenones (30,31). They are employed for brightening synthetic fibers such as polyamides, cellulose acetates, and polyacrylonitriles. 

The photorearrangement of pyrazoles to imidazoles is probably analogous, proceeding via iminoylazirines (82AHC(30)239) indazoles similarly rearrange to benzimidazoles (67HCA2244). 3-Pyrazolin-5-ones (56) are photochemically converted into imidazolones (57) and open-chain products (58) (70AHC(ll)l). The 1,2- and 1,4-disubstituted imidazoles are interconverted photochemically. 

Scheme 19 contains all the reactions observed in different examples, none being so complex (B-76MI40402). Most studies deal with the methylation of 3-methyl-1-phenyl-pyrazolone, since in this case one of the products obtained is antipyrine (2,3-dimethyl-l-phenyl-3-pyrazolin-5-one), one of the classical antipyretic agents (Section 4.04.4.1.1). 

Sulfonation of 2- and 3-pyrazolin-5-ones occurs at position 4. Thus 3-methyl-1-phenyl-pyrazolin-5-one with 20% oleum at 10-15 °C yields the corresponding 4-sulfonic acid (304) (64HC(20)l). Higher temperatures cause sulfonation not only of the heterocycle but also of the phenyl group. Antipyrine treated with sulfuric acid and acetic anhydride yields (305). 

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). 

Forbisen, 2,2, 3,3 -tetramethyl-l,l -diphenyl-4,4 -bi-3,3 -pyrazoline-5,5 -dione (706) (B-76MI40404), a by-product obtained in the manufacture of antipyrine, has been used in bovine anaplasmosis. 

Finally, benzpiperylon or l-(l-methyl-4-piperidyl)-3-phenyl-4-benzyl-2- (or 3-) pyrazolin-5-one has been utilized by Sandoz as an investigational agent in connective tissue disorders (B-76MI40404). 

Methyl-l-phenyl-3-pyrazolin-5-one gives a green-black dye (736) with 4-nitroso- or 4-amino-dimethylaniline and silver chlorides in the presence of light, a process of great importance in colour photography (B-76MI40403). 

Pyrrolidino[l,2-6][l,3,4]oxadiazoline, 5-phenyl-biological activity, 6, 1024 Pyrrolidino[2,1 -6][1,3]oxazolidines synthesis, 5, 137 Pyrrolidino[l,2-6]pyrazolines synthesis, 5, 148... 

Dippii solution I Dissolve 1 g 4-aminoantipyrine (4-aminophenazone 4-ami-no-2,3-dimethyl-l-phenyl-3-pyrazolin-5-one) in 100 ml 80% ethanol. 

In order to synthesize 1,3-diphenyl-l, 3-diamines 3 containing a C2 axis of symmetry, which can be employed as auxiliaries and controller groups in asymmetric syntheses, the diastereoselective addition of organometallic reagents to racemic pyrazolines 2, prepared from cinnamaldehyde (l)23, was investigated. 

Dimethyl-l-phenyl-3-pyrazolin-5-one, a299 Dimethyl propanedioate, d630... 

Imidazole, purification of, 48, 45 reaction with phosgene, 48, 44 Imldazole, 1,1 -carbonyldi-, 48, 44 Imidazolium chloride, 48, 46 3-Imino-l-( -tolylsulfonyl)pyrazolidine, from 3-amino-3-pyrazoline sulfate and / -toluenesulfonyl chloride, 48, 9... 

Xiao D, Xi L, Yang W, Fu H, Shuai Z, Fang Y, Yao J (2003) Size-tunable emission from l,3-diphenyl-5-(2-anthryl)-2-pyrazoline nanoparticles. J Am Chem Soc 125 6740-6745... 

Peng AD, Xiao DB, Ma Y, Yang WS, Yao JN (2005) Tunable emission from doped l,3,5-triphenyl-2-pyrazoline organic nanoparticles. Adv Mater 17 2070-2073... 

This paper discusses the synthesis and physico-chemical consequences of binding low ionization 17-donors, such as TTF monocarboxylic acid (I) and l,3-di-(p-methoxyphenyl)-5-(p-hydroxyphenyl)-A2-pyrazoline (II) to a poly(vinylbenzylchloride) backbone. 

The transition metal-catalyzed reaction of diazoalkanes with acceptor-substituted alkenes is far more intricate than reaction with simple alkenes. With acceptor-substituted alkenes the diazoalkane can undergo (transition metal-catalyzed) 1,3-dipolar cycloaddition to the olefin [651-654]. The resulting 3//-pyrazolines can either be stable or can isomerize to l//-pyrazolines. 3//-Pyrazolines can also eliminate nitrogen and collapse to cyclopropanes, even at low temperatures. Despite these potential side-reactions, several examples of catalyzed cyclopropanations of acceptor-substituted alkenes with diazoalkanes have been reported [648,655]. Substituted 2-cyclohexenones or cinnamates [642,656] have been cyclopropanated in excellent yields by treatment with diazomethane/palladium(II) acetate. Maleates, fumarates, or acrylates [642,657], on the other hand, cannot, however, be cyclopropanated under these conditions. 

C-4 protonation would be expected to occur preferentially in 3-pyrazolines. It is in fact found that the thermodynamically stable conjugate acid is protonated on C-4 (Aubagnac et al., 1967a and 1969), but a transitory existence of an N-protonated form could also be demonstrated (Aubagnac et al., 1967b). This was identified as N-1 protonated by measurements of chemical shifts caused by protonation of l,2,4-trimethyl-3-phenyl-3-pyrazoline [158]. The signal of... 

The reaction of aroylhydrazines with DMAD gives rise to the hydrazones of oxaloacetic ester, which undergo thermal transformation to the corresponding diaroylhydrazines. b. Hydrazones. Ethyl l,3,5-triphenylpyrazole-4-carboxylate has been reported to be formed in the reaction of benzaldehyde phenylhydrazone with ethyl phenylpropiolate. In a detailed investigation, George and co-workers have shown that aldehyde phenylhydrazones react with DMAD, yielding a mixture of pyrazoles and pyrazolines. Thus, in the reaction of benzaldehyde phenylhydrazone with DMAD, products such as dimethyl l,3-diphenylpyrazoline-4,5-dicarboxylate (129), dimethyl... 

Antipyrine 2t3- imetbyl-l pkenyl-3 pyrazolin 3 one or Pbenazone, listed in Beil as 1-Phenyl-2.3 dimethyI-pyrazolon-(5) or... 

An interesting preparation of aliphatic diazoalkanes (R R2C = N2 R1, R2 = alkyl) involves the photolysis of 2-alkoxy-2,5-dihydro-l,3,4-oxadiazoles (see Scheme 8.49). When the photolysis is carried out in the presence of an appropriate dipolarophile, the diazo compounds can be intercepted (prior to their further photolysis) by a [3 + 2] cycloaddition reaction (54). As an example, 2-diazopropane was intercepted with A-phenylmaleimide (54) and norbornenes (55) to give the corresponding A -pyrazolines. 

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