5-hydroxy-pyrazole-3-carboxylic acids

Our explorative chemistry approach was considerably facilitated by the fact that a variety of a-, p-, y-amino acid derivatives is commercially available. And the other starting material - the 5-hydroxy-pyrazole-3-carboxylic acids - for the amide coupling reaction delivering our target molecules was accessible by only one synthetic step (Scheme 23.2) [2]. 

Pyridazinones may undergo ring contraction to pyrroles, pyrazoles and indoles, the process being induced either by an acid or base. The structure of the final product is strongly dependent on the reaction conditions. For example, 4,5-dichloro-l-phenylpyridazin-6(lFT)-one rearranges thermally to 4-chloro-l-phenylpyrazole-5-carboxylic acid (12S), while in aqueous base the corresponding 4-hydroxy acid (126) is formed (Scheme 40). 

Hydroxy-6-methyl-2-phenylpyridazin-3(2Fr)-one and 4-hydroxy-5-nitropyridazin-3(2FT)-one rearrange in acidic medium to 3-methyl-l-phenylpyrazole-5-carboxylic acid and 4-nitropyrazole-5-carboxylic acid. 4-Hydroxypyridazin-3(2FT)-ones with a hydroxy group or other group at positions 5 or 6, which is easily replaced in alkaline medium, are transformed into 5-(or 3-)pyrazolones with hot alkali. An interesting example is ring contraction of 5-chloro-4-(methylthio)-l-phenylpyridazin-6(lFT)-one which gives, besides pyrazole derivative (127), 4-hydroxy-5-methylthio-l-phenylpyridazin-6(lFf)-one (128 Scheme 41). 

Thieno[3,4-d]oxazole-3a(4H)-carboxylic acid, dihydro-2-methyl-synthesis, 6, 1020 Thieno[2,3-d Joxazoles synthesis, 6, 990 Thieno[3,2-g]pteridine structure, 3, 284 lH-Thieno[3,4-c]pyran-2-ones synthesis, 4, 1032 Thienopyrazines synthesis, 4, 1022-1024 Thieno[2,3-6]pyrazines, 4, 1023 electrophilic substitution, 4, 1024 Thieno[3,4-6]pyrazines, 4, 1024 Thieno[3,4-c]pyrazole, 4,6-dihydro-3-hydroxy-carbamates... 

A method frequently used to determine aromatic amines in water-soluble dyes involves their extraction with chloroform, followed by diazotization of amines and coupling of diazonium salts with a reagent R-salt (disodium-3-hydroxy-naphthalene-2,7-disulfonate) or pyrazolone T (4,5-dihydro-5-oxo-l-(4-sulfophenyl-)l/7-pyrazole-3-carboxylic acid). The separated products are detected by UV-VIS spectrophotometry or fluorescence (210-212). 

H-Pyrazole-3-carboxylic acid, 4,5-dihydro-5-oxo-l-(4-sulfophenyl)-4-[(4-sulfophenyl)azo]-trisodium salt — see Tartrazine Pyrazole-5-carboxylic acid, 4-hydroxy-synthesis, 5, 276 Pyrazolecarboxylic acids decarboxylation, 5, 260 reactions... 

From 3(5)-hydroxypyrazoles. 5-Hydroxy-l-phenyl-lH-pyrazole-4-carboxylic acid ethyl ester 303, derived from diethyl (ethoxymethylene)-malonate and phenylhydrazine hydrochloride, when methylated with dimethyl sulfate in aqueous sodium hydroxide solution afforded pyrazole 304 together with pyrazol-3-one 305 in 16% and 33% yield, respectively (95JHC1341) (Scheme 68). 

Dihydro-5-oxo-l- 4-sulfophenyl)-4-[ 4-sulfopheny[)azo -lH-pyrazole-3-carboxylic acid, 9CI. 5-Hydroxy-1- 4-sulfophenyl)-4-l 4-sulfophenyl)azo pyrazole-3-carboxylic acid. Hydrazine yellow. C.I. Food yellow 4. C.I. Acid yellow 23, SCI... 

Hydroxy-1 -naphthalenyl) azoj-1 //-pyrazole-4-carboxylic acid, see H-00353... 

---