4-Amino-3-pyrazolin-5-ones acylation

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 amino group of 4-amino-3-pyrazolin-5-ones reacts normally. Acylation occurs readily with a wide variety of acylating agents. Amides are formed by reaction with acid chlorides,50,533,984,1414,1473 acids618,984,1471 and esters in the presence of phosphorus pentoxide.1471 Thioformamides have been prepared by reaction with dithioformic acid and its salts.472,556,1374 Sulfonyl chlorides react to form sulfonamides.98,489,984,1249,1504 Chlorophosphates react with 4-amino-3-pyrazolin-5-ones to form phosphoramide derivatives.509,1498... 

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... 

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