4-Amino-3-pyrazolin-5-ones alkylation

A mechanism has been proposed to rationalize the results shown in Figure 23. The relative proportion of the A -pyrazolines obtained by the reduction of pyrazolium salts depends on steric and electronic effects. When all the substituents are alkyl groups, the hydride ion attacks the less hindered carbon atom for example when = Bu only C-5 is attacked. The smaller deuterohydride ion is less sensitive to steric effects and consequently the reaction is less selective (73BSF288). Phenyl substituents, both on the nitrogen atom and on the carbon atoms, direct the hydride attack selectively to one carbon atom and the isolated A -pyrazoline has the C—C double bond conjugated with the phenyl (328 R or R = Ph). Open-chain compounds are always formed during the reduction of pyrazolium salts, becoming predominant in the reduction of amino substituted pyrazoliums. 

Pyrazblin-5-one, 3-alkyl-(l,2,4-thiadiazol-5-yl)-reactions, 6, 483 2-Pyrazolin-5-one, 3-amino-tautomerism, 5, 215 2-Pyrazolin-5-one, 4,4-diazido-rearrangement, 5, 720 2-Pyrazolin-5-one, 3-hydroxy-tautomerism, 5, 215 2-Pyrazolin-5-one, 3-methyl-1 -phenyl-reactions, 5, 252... 

Pyran, tetrahydro-, 3 chloro 2 methyl [2H Pyran, tetrahydro, 3 chloro-2-mcthyl ], cis, trans mixture, 55, 64 2-PYRAZOLIN-5-ONES, 3-alkyl-, 55, 73 2-Pyrazolin 5-one, 3-(l-propyl)-, 55, 73 Pyridine, 2-amino-, p-bromination of, 55, 23... 

The 4-amino-2-pyrazolin-5-ones react as do other amines. They can be alkylated with alkyl halides992 and react with aldehydes to form Schiff bases.633"2 Oxidation of these amino compounds with ferric chloride leads to the rubazonic acids (eq. 178) in which two 2-pyrazolin-... 

Most syntheses of tertiary amino-3-pyrazolin-5-ones are based on an alkylation by one means or another of the primary or secondary amino analogs. In some cases simultaneous reduction of a nitroso or nitro compound or of a Schiff base and alkylation of the amine so formed is carried out. 4-Dimethylamino-3-pyrazolin-o-ones (amino-... 

A variety of 4-amino-5-alkoxy- and acyloxy-l,3-disubstituted-pyrazoles have been treated with alkylating agents such as alkyl halides to give 4-dialkylamino-3-pyrazolin-5-ones.525 There is a simultaneous alkylation of ring nitrogen and extranuclear nitrogen. 

The alkylation of 4-amino-3-pyrazolin-5-ones has already been discussed to a considerable extent in connection with the preparation of such compounds having two substituents on the extranuclear nitrogen atom (see p. 76). The most straightforward alkylation is that with alkyl halides.101,431 Alkylation by means of formation of the Schiff base with aldehydes or ketones followed by catalytic reduction has frequently been used.111,131,1303 Treatment of 4-amino-2,3-dimethyl-l-phenyl-3-pyrazolin-5-one with formaldehyde and sodium bisulfite in 5 ... 

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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