Imino-3-pyrazolines

Imino-2-pyrazolin-5-ones of the type (XXIX) have become very important in the field of color photography and will be discussed in... 

For purposes of classification the 4-aminopyrazoles are considered to be 4-imino-2-pyrazolines and analogs of 2-pyrazolin-4-ones. These compounds are listed in Table XL. Such compounds can be prepared by direct cyclization using ethyl diazoacetate and ethyl cyanoacetate.92 This is the same as eq. 243, except that the malonic ester is replaced by ethyl cyanoacetate. Purines can be hydrolyzed to 4-imino-2-pyrazolines by using strong acid.1210 1846 By far the most frequently used preparation is reduction of appropriately substituted pyrazoles, such as 4-nitro,368,812,819,1015,1019,1049 4-nitroso1165 or 4-aryl-azo.671 974,995 The hydrolysis of the carbethoxy 4-imino-2-pyrazolines derived from ethyl cyanoacetate and ethyl diazoacetate forms 4-imino-2-pyrazolin-3-carboxylic acid which is readily decarboxylated to the parent compound.92... 

The 4-imino-2-pyrazolines react as would be expected of 4-amino-pyrazoles. For example, acylation368,1043 and diazotization812,819 occur readily. 

Only two bis(4-imino-2-pyrazolines) have been prepared. These were reported by Michaelis and Schafer.995... 

Only half-a-dozen of these compounds are known (Table XLI) and at least this number of methods of preparing them have been reported. Borsche and Manteuffel125 have found that 2-pyrazolin-4,5-diones are formed as the by-products when oc-ketoesters are treated with aryl-diazonium salts. The principal products are 4-arylazo-2-pyrazolin-5-ones. Nitric acid oxidation of 3-methyl-l-phenyl-2-pyrazolin-5-one forms the corresponding 4,5-dione.809 Wislicenus and Gtiz1842 heated 4 -bromo - 4 - nitro -1 - (4 - bromophenyl) - 3 - methyl - 2 -pyrazolin - 5 - one in water and obtained the analogous 4-oxo compound. Acid hydrolysis of rubazonic acids, which are 4-imino-2-pyrazolin-5-ones, leads to 2-pyrazolin-4,5-diones.424 809 Oxidation of 4,4 -bis(2-pyrazolin-5-ones) or of rubazonic acids with nitric acid809 forms the 4,5-diones. 

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... 

VII), since Glauert and Mann578 found no imino or hydroxyl absorption in the infrared spectra of l,4-diaryl-2-pyrazolin-5-ones. Recently366a the infrared spectra of 3-methyl-, 3-trifluoromethyl-,... 

Alphen1513 it is also obtained by the reductive cyclization of a crotonic ester (eq. 56). The replacement of a 4-imino function in a 2-pyrazolin-5-one by a 2-pyrazolin-5-one lacking a 4-substituent also leads to a... 

It is probable that most of the 5-imino-2-pyrazolines exist as the corresponding aminopyrazoles (XXIV). Gagnon, Boivin and Trem-... 

Several methods for the synthesis of 5-imino-2-pyrazolines depend upon the amination of a pyrazole ring. 5-Chloropyrazoles react with aniline to give the corresponding 5-amino compound.826,1002 The chloropyrazoles can be prepared and amination accomplished in one... 

Cusmano340 341,345 has converted 5-alkyl- and 5-arylisoxazole-3-carboxylic acids into 5-imino-2-pyrazolines by treatment with phenyl hydrazine. Musante has also used this procedure.1043-1045 This reaction goes by way of /J-ketonitrile intermediates and gives very poor yields.86... 

The decarboxylation of l,3-diphenyl-5-imino-2-pyrazolin-3-carboxylic acid gives l,3-diphenyl-5-imino-2-pyrazoline.506 Druey and Schmidt391 have taken advantage of the selective replacement of an oxo group by chlorine over that of an imino group to prepare 5-imino-2-pyrazolines (eq. 95). 

Druey and Schmidt391 have reported that alkylation of N-l unsubstituted 4,4-dialkyl-5-imino-2-pyrazolines with dimethyl sulfate occurs at the N-l position. 

Moureu and Lazennec1025 were unable to hydrolyze 3-alkyl-5-imino-2-pyrazolines to the 5-oxo analogs, but Cusmano340 claims to... 

Michaelis996 has reported that oxidation of various 5-imino-2 pyrazolines with hydrogen peroxide or nitrous acid gives what were called azipyrazoles of type (XXVI). It seems highly unlikely that these... 

A few bis(2-pyrazolin-5-ones) having one or both 5-oxo groups replaced by imino groups have been prepared. The preparation of those having one imino group is shown in eqs. 99 and 100. Those linked... 

A number of 5-imino-3-pyrazolines are known and are listed in Table XIX. Those which have no substituent at N-l can exist as... 

Pyrazolin-5-one hydrochlorides react with hydrazines at about 100° to form 5-imino compounds (eq. 155).983 A similar reaction has... 

A few 5-imino- and 5,5 -iminobis(3-pyrazolines) are listed in Table XV. These are prepared by reaction of the appropriate chloropyrazole methiodide with ammonia.991... 

The few 3-acyloxy-5-imino-2-pyrazolines known are prepared by acylation of 5-imino-3-pyrazolidinones.391,594,1599 Crippa and Gau-meri32 have treated 3-methyl-l-phenyl-5-imino-2-pyrazoline with p-nitrophenylsulfenyl chloride to obtain a 4-arylmercapto compound. These compounds are listed in Table XII. 

All of these derivatives of 2-pyrazolin-5-ones have a nitrogen atom substituted at the 4-position as the 3-nitrogen-substituted-2-pyrazolin-5-ones are tautomeric with the 5-imino-3-pyrazolidinones and are considered as such in this discussion. The 4-nitrogen-substituted-2-pyrazolin-5-ones are not usually prepared by cyclization directly to the desired pyrazolinone ring but rather by modification of already formed pyrazolinones. The methods used are usually those employed in... 

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