Acetic Acid → 6-[1-(1H-imidazol-1yl)-2-methylpropyl]-3-propyl-2(1H)-quinoxalinone

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To a stirred and cooled (0° C.) mixture of 9 parts of 4-[1-(1H-imidazol-1-yl)-2-methylpropyl]-1,2-benzenediamine in 80 parts of acetic acid and 20 parts of water were added 5 parts of 2-oxopentanoic acid. The reaction mixture was stirred for 12 hours at room temperature. The whole was poured into ice water and neutralized with a sodium hydroxide solution 3N. The product was extracted three times with 130 parts of dichloromethane. The combined extracts were dried, filtered and evaporated. For obtaining 6-[1-(1H-imidazol-1yl)-2-methylpropyl]-3-propyl-2(1H)-quinoxalinone, the residue was purified by column chromatography (HPLC) over silica gel using a mixture of dichloromethane and methanol (98:2 by volume) as eluent. The pure fractions were collected and the eluent was evaporated. The residue was crystallized from a mixture of 2-butanone and 1,1'-oxybisethane. The precipitated product was filtered off and stirred in cold 4-methyl-2-pentanone. After filtration, the product was recrystallized from a mixture of methanol and 2-propanone, yielding 1.6 parts (13.2%) of the above product; mp. 259.7° C. (comp. 100).

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