Background: A facile, effective, new and green methodology has been developed for the
synthesis of 3,3-di(indolyl)indolin-2-one through electrophilic condensation reaction of indole derivatives
with various isatins in the presence of 1,4-diazabicyclo[2.2.2]octanium diacetate as an efficient
homogeneous media under grinding. This work consistently has advantages as excellent yields, short
reaction time, mild condition and simple work-up procedures. The catalyst could be easily recovered
and reused for six cycles with almost consistent activity. All of the synthesized compounds were characterized
by their physical constant, comparison with authentic samples, IR, 1H NMR, 13C NMR spectroscopy
and elemental analysis.
Methods: A mixture of isatin derivatives (1 mmol) or synthesized bis isatin (0.5 mmol), indole derivatives
(2 mmol) and [DABCO] dihydroacetate (0.5 mmol) were added to a mortar and the mixture was
pulverized with a pestle for the required reaction time. After completion of the reaction, as indicated by
TLC, the reaction mixture was dissolved in 20mL of H2O. The product was separated by filtration and
recrystallized from EtOH and dried to afford powdery compounds 3a-n. The filtrate was concentrated
under reduced pressure and washed with diethyl ether. Then, it was dried in a vacuum evaporator to
recover the ionic liquid for subsequent use.
Results: In continuation of our ongoing studies to synthesize heterocyclic and pharmaceutical compounds
under mild and practical protocols, herein we wish to report our experimental results on the
synthesis of 3,3-di(indolyl)indolin-2-one using various isatins and indoles in the presence of novel
ionic liquid ([DABCO]diactate). After the reaction, the used ionic liquid was separated and recycled to
use for the next reaction run. Our experiments also indicated that after five runs, the catalytic activities
of the reagents were almost the same as those of fresh catalysts.
Conclusion: In conclusion, we have investigated DABCO-diacetate as a mild and efficient catalyst for
the synthesis of oxindoles. This method should be useful from the industrial point of view because it is
high yielding and time saving under solvent free condition. DABCO-diacetate is inexpensive, nontoxic,
easy to handle, and can act as a green medium. Simple work-up procedure, short reaction times,
high yields of product with better purity, and green aspect due to the recyclability of media are major
advantages of this protocol.