A reinvestigation of reaction of 2-hydrazino-3-phenylquinoxaline with 1,3-diketones: Synthesis and characterization of regioisomeric 1-(3′-phenylquinoxalin-2′-yl)-3,5-disubstitutedpyrazoles and 1,2,4-triazolo[4,3-a]quinoxalines

A reinvestigation into the reaction of 2-hydrazino-3-phenylquinoxaline 1 with several 1,3-diketones 2a-g reveals that a mixture of regioisomeric 1-(3'-phenylquinoxalin-2'-yl)-3,5-disubstitutedpyrazoles 3a-g and 4a-e and 1-methyl-4-phenyl/methyl-1,2,4-triazolo[4,3-a]quinoxalines 5a,b is formed as reaction products rather than erroneously reported exclusive formation of triazole 5 in case of aryl alkyl-1,3-diketones or 1-(3'-phenylquinoxalin-2'-yl)-3-alkylpyrazoles 4 in case of dialkyl and diaryl-1,3-diketones. Structural elucidation of the regioisomeric pyrazoles has been established by the spectroscopic data (H-1, C-13 NMR, COSY experiments and FIRMS) and minimum energy 3-D diagrams.