Treatment of 2-hydrazino-3-methylquinoxaline (1) with phenyl-1,3-butanedione (2b) in THF affords regioisomeric 1-(3'-methylquinoxalin-2'-yl)-3(5)-methyl-5(3)-phenylpyrazoles (3b and 4b) as major products along with the formation of small amount of 1,4-dimethyl-1,2,4-triazolo[4,3-a]quinoxaline (5) rather than the reported exclusive formation of 5. Several other regioisomeric 1-(3'-methylquinoxalin-2'-yl)-3,5-disubstituted pyrazoles have similarly been synthesized using other aryl-and heteroaryl-1,3-diketones. The identity of the regioisomeric pyrazoles is based upon NMR ( 1 H & 13 C) spectral data and an unambiguous synthesis.
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