5-Amino-3-arylpyrazoles

The data about MCRs involving 5-amino-3-arylpyrazoles are more discrepant. Quiroga et al. [82] reported three-component treatment of this pyrazole with dime-done and aromatic aldehydes in boiling ethanol, yielding only pyrazoloquinolinones... 

Treatment of arylidenepyruvic acids 236 with 5-amino-3-arylpyrazoles 222 (R is Ar, Ri is H) in most cases was not regioselective and yielded mixtures of several regioisomers and products of their heteroaromatization 2,7-diaryl-4,7-dihydropyrazolo[l,5-tf]pyrimidine-5-carboxylic acids 246 (main product), 3,4-diaryl-4,7-dihydropyrazolo[3,4-Z ]pyridine-6-carboxylic acids 247 and their heteroaromatized derivatives 248 (Scheme 3.68). 

The rearrangement of 2-amino-5-aryl-6//-l,3,4-thiadiazines (57 R = Ar) in hot acetic acid has some merit as a synthetic route to 5-amino-3-arylpyrazoles (62 R = Ar) <87Mi 6l7-0l>. The yields of pyrazole increase markedly relative to those obtained from the 6-unsubstituted thiadiazine (57 ... 

However, further a possibility of the formation of several different reaction products in similar processes was reported [97-99]. With the help of microwave irradiation and ultrasonication, the problem of selectivity was also touched in these communications. It was found that three-component reaction of equimolar mixture of 5-amino-Al-arylpyrazole-4-carboxamides, aldehydes, and cyclic (3-diketones in DMF under conventional thermal heating or under microwave irradiation at 150°C yielded pyrazoloquinazolines 68. The treatment at room temperature under ultrasonication gave the same reaction products, although addition of catalytic amounts of hydrochloric acid changed direction and positional isomeric quinazolines 69 were only isolated in this case. 

Substitution and cyclization of the tertiary amino group of aminomethyleneketones by hydrazine leads to 3-formylpyrazole in good yield (equation 193). In the same way 2-pyrazolylpyridine is accessible in high yield (equation 194). Even specially substituted 3-arylpyrazoles and 4-arylpyrimidines are thus accessible in good yield (equation 195). 

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