Synthesis of fused tetrahydro-β-carbolinequinoxalinones in 1-n-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([bdmim][Tf2N]) and 1-n-butyl-2,3-dimethylimidazolium perfluorobutylsulfonate ([bdmim][PFBuSO3]) ionic liquids

Starting from tryptophan methyl ester, a three-step synthesis of fused tetrahydro-β-carbolinequinoxalinones in two new ionic liquids, [bdmim][Tf2N] and [bdmim][PFBuSO3], was described. Both ionic liquids can be readily prepared from commercially available starting materials in high yields. Unlike the commonly used [PF6]-based ionic liquids that evidently undergo slow hydrolysis of the PF6 anion with the concomitant release of HF, ionic liquids of [bdmim][Tf2N] and [bdmim][PFBuSO3] are not only chemically stable but also apparently inert to hydrolysis and therefore organic reactions carried out in both ionic liquids proceed smoothly with good yields. The overall isolated yields for this three-step synthesis of tetrahydro-β-carbolinequinoxalinones were 34–55%. To the best of our knowledge, the preparation of fused tetrahydro-β-carbolinequinoxalinones was unprecedented.