Deep eutectic solvents (DESs) are a class of ionic liquids (ILs) successfully implemented for many organic transformations.1,2 Several reports have shown the immense potential of using ILs with ultrasound, as the blend of these two practices can fulfill several important criteria of green chemistry. Indoles are key heterocyclic systems, present in naturally-occurring compounds such as tryptophan, serotonin, melatonin, tryptamine, and plant growth hormones, as well as synthetic materials.9 Their varied biological activities have made them of much interest. In the development of the latter, an important focus of research has been on functional-ization at the C-3 position.10 Numerous reports have been published on the synthesis of 3-substituted indoles by using such techniques as the electrochemical approach,11 such catalysts as copper(II) sulfonate salen,12 Zn(II) salen,13 2-pyrrolecarbaldiminato-Cu(II) complexes,14 hybrid nanoparticles H5PW_(10)V2O_(40)@VOx/SBA-15-NH2)15 H3PW_(12)O_(40)/SBA-15,16 L-proline,17 PEG-400,18 PEG-200,19 tetrabutylammonium fluoride,20 and such ILs as tetrabutylammonium glycinate.21
展开▼
