Pyrazole. alkylation nitration

We have already noted (Section 4.04.2.1.4(xi)) that alkyl groups on pyrazoles are oxidized with permanganate to carboxylic acids. Silver nitrate and ammonium persulfate transform 4-ethyl-1-methylpyrazole (436) into the ketone (437) (72JHC1373). The best yield was obtained starting with the alcohol (438) and using an acid dichromate solution as oxidizing agent. 

An important development of the synthesis described above is derived from the observations of Scott, O Donovan and Reilly [159], which were taken up by others [109]. l-Guanyl-3,5-dimethylpyrazole nitrate reacts with alkyl- and aryl-amines in hot water, ethanol, or without solvent to give good yields of guanidines. Use of this pyrazole nitrate or other salt for obtaining guanidines now competes with older methods if yield and ease of isolation of the product are the main considerations [95, 138, 140, 143, 160-164]. 

Only a few reports have dealt with the behavior of tetra-azaindenes toward electrophiles, and the reactions reported involved the pyrazole ring. Thus, alkylation of 336 with alkyl halides affords a mixture of the A-alkylated derivatives 337 and 338. Compound 336 is produced by alkylation of 339. Bromination of 339 (R = H) affords the 7-bromo derivative 340 (82JHC817) (Scheme 34). Nitration of 2-methylpyrazolo[3,4-c] pyridazine occured at pyrazole C-3 (73JAP76893). Bromination of 341 with bromine in acetic acid gives 342 (83AP697). 

Chloroperoxidase catalysis by, 58, 302 in chlorination of pyrazoles, 57, 337 Chlorophyll, thioaldehyde synthetic intermediate to, 55, 3 Chlorosulfonyl isocyanate, reaction with 2-arylhydrazono-3-oxobutanoate, 59, 148 Chromatography, of [l,2,4]triazolo[l,5-a]-pyrimidines, 57, 106 Chrom-3-enes, see 2//-l-Benzopyrans Chromium tricarbonyl complexes of 3,5-diphenyl-l-(alkyl- or oxido-)-thiabenzenes, 59, 206, 227 indoles, lithiation of, 56, 181, 184 of pyridine, 58, 160 pyridines, lithiation of, 56, 230, 239 of 2f/-thiopyrans, 59, 227 Chromones, see l-Benzopyran-4-ones Cinnamonitrile, a-cyano-, condensations with thio-, seleno-amides, 59, 184, 186 Cinnoline, nitration, MO calculation, 59, 302... 

Die aus 3-Oxo-alkansaure-estem mit Hydrazin leicht zuganglichen 3-Alkyl-5-oxo-4,5-dihydro-pyrazole werden in methanolischer Losung durch Thallium(III)-nitrat zu 2-A1-kinsaure-estern oxidiert303 ... 

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