5- Imino-3-pyrazolidinones

Amino-3-pyrazolin-5-ones (4-imino-3-pyrazolidinones) react with nitrous acid as do ordinary aromatic amines to form diazonium salts.426,984,1353 These then couple readily with aromatic amines,1017,1018,1060 phenols992,1323 and aliphatic compounds having active hydrogen atoms,428,1017 such as acetoacetic esters. The products are 4-azo-3-pyrazolin-5-ones (eq. 200). The diazonium salts also couple... 

TABLE XLVI. Miscellaneous Bis(3,5-pyrazolidinediones), Bis(5-imino-3-pyrazolidin-ones), and Bis(4-imino-3-pyrazolidinones)... 

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... 

The 5-oxo-3-pyrazolincarboxylic acids react normally. A number of their reactions have already been discussed in connection with the synthesis of analogous aldehydes and ketones. The Curtius rearrangement of the azide will be discussed in more detail in the section concerning 5-imino-3-pyrazolidinones. Both the 3- and 4-carboxylic acids decarboxylate at elevated temperatures.107,108,370 Hydrolysis of 4-carboxanilides with hydrochloric acid first forms the acid which then loses carbon dioxide.826... 

The 5-imino-2-pyrazolines having no N-l substituents can be acylated with acetic anhydride to form the 1-acyl derivatives,301,342,391 as can their 5-oxo analogs. Compounds of this type having a 3-acetoxy substituent have been prepared by reaction of 3-amino-2-pyrazolin-5-ones (5-imino-3-pyrazolidinones) with acetic anhydride (eq. 237).594,1598 Cusmano and Sprio343,344 have treated a-benzylidene-j8-ketonitriles... 

The reaction of 5-imino-3-pyrazolidinones with acetic anhydride forms 2-acetyl-3-acetoxy-5-acetimido-3-pyrazolin-5-ones as well as the 5-imino-2-pyrazoline derivatives already mentioned.594-1599... 

Synthetic methods involving conversion of other, but similar, ring systems to 3,5-pyrazolidinediones have been reduction of 1,2-diphenyl-3,4,5-pyrazolidinetrione with tin and hydrochloric acid63 and hydrolysis of 5-imino-3-pyrazolidinones (3-amino-2-pyrazolin-5-ones) with acid.1339,1596... 

The most frequently used procedures for preparation of 5-imino-3-pyrazolidines can all be considered as variations of cyclization of malonic acid derivatives. Various hydrazines react with ethyl /3-amino-/ -ethoxyacrylate to form 2-substituted-5-imino-3-pyrazolidinones (eq. 261). Complex alkyl groups,706 aryl groups693,695,922,1140,1601 and... 

One of the most widely used methods for the preparation of 5-imino-3-pyrazolidinones is from 5-oxo-3-pyrazolin-3-carboxylic acids or their derivatives by use of the Hofmann167,697 or Curtius167,1387,1395 rearrangements (eq. 264). A similar synthesis is from the analogous... 

Acylation of 5-imino-3-pyrazolidinone can occur at several places. Most commonly reaction occurs at the 5-imino group and further reaction then may occur by acylation of the enol form of the 5-oxo group. 

In compounds which have no substituents at N-l or N-2 nuclear acylation also occurs and under some conditions acylation occurs at C-4. The use of 2-alkyl- or aryl-5-imino-3-pyrazolidinones, which exist as the 3-amino-2-pyrazolin-5-one isomer, with an equivalent of acid chloride, either aliphatic or aryl, leads to 3-acylamides (eq. 266),14,67,594,695,1247,1594,1595 although in some cases a side-reaction gives both N- and O-acylation.1595 Under the same conditions 3-hydroxy-5-imino-2-pyrazolinones give O-acylation.1599 The reaction of... 

The reactions undergone by 5-imino-3-pyrazolidinones are in general very similar to those of 2-pyrazolin-5-ones. The hydrogen atoms at C-4 are active and this position is the reactive center in the nucleus of these molecules. Condensation with aldehydes and ketones occurs with formation of benzylidene644,1083 or 4,4 -benzylidenebis... 

Imino-3-pyrazolidinones having functional group substituents are listed in Sections B and C of Table XLIX. These compounds are usually synthesized by procedures which are used for introduction of the same substituents into previously discussed pyrazolinone and pyrazolidinone systems. 

Bromo-5-imino-3-pyrazolidinones are synthesized by Curtius rearrangement of the azides of 4-bromo-5-oxo-3-pyrazolin-3-carboxylic acids.697 4-Nitroso-5-imino-3-pyrazolidinones are believed to exist as the oximino tautomers.337 They are usually prepared by direct nitro-sation with nitrous acid.644-1339 1649 A Curtius rearrangement of 4-oximino-5-oxo-2-pyrazolin-3-carboxylic acid azide has also been used.337... 

Amino-5-imino-3-pyrazolidinones have been synthesized by reduction of the corresponding oximes.644,1339 Such amines form ureas and thioureas by reaction with potassium cyanate in acid solution and with phenyl isothiocyanate.644 4-Arylimino-5-imino-3-pyrazolidinones have been prepared by reaction of the 5-imino-3-pyrazolidinones with p-amino-A.-AT-diethylaniline in the presence of silver salts as oxidizing agents (eq. 172).244,519,1255,1538 4-Arylazo-5-imino-3-pyrazolidinones have most frequently been prepared by reaction of 5-imino-3-pyrazoli-dinones with aryldiazonium chlorides, as is usual for the preparation of similar compounds.591,594,920,1087,1255,1339,1539,1649 One such compound has been prepared by the Curtius rearrangement of the corresponding 4-arylazo azide.594... 

The preparation of C-4 acyl and N-l and N-2 acyl 5-imino-3-pyrazolidinones has been partially discussed in the preceding section. 4-Acetyl-5-imino-3-pyrazolidinones have been prepared by reaction of ethyl acetylcyanoacetate with phenylhydrazine (eq. 263, R1 = CH3CO, R2 = H).498 4-Carbethoxy derivatives of 5-imino-3-pyrazolidinones have been prepared in two ways. One of these was by the cyclization procedure shown in eq. 271.1650 The second method is direct introduction... 

Amino-5-imino-3-pyrazolidinones react with formaldehyde at the 4-amino group giving methylol derivatives.644 The 4-arylimino derivatives are reduced catalytically to give 4-arylamino analogs.1538 An interesting reaction of the 4-arylazo-5-imino-3-pyrazolidinones is the replacement of the 4-arylazo group by arylimino (eq. 272).1255 1296... 

Bis(5-imino-3-pyrazolidinones) linked at the 4,4 -positions by one or two atoms of sulfur are known (Table L) and their preparation was mentioned in the previous section. 

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