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A. B. ATAR ET AL.
inexpensive, safe, and environmentally non-hazardous.[2] Most importantly they are
immiscible with a number of organic solvents which provide nonaqueous, polar alterna-
tive for two-phase systems instead of the use of water. Recently ionic liquids have been
considered as a new class of green solvents.[3] Moreover, ionic liquids have great ability
to control the selectivity of chemical transformations as well as reduce the time of com-
pletion reaction. Therefore, the development of synthetically useful reactions in ILs is of
considerable interest in the scientific community.[4]
Currently, there has been increasing concern with regard to the tight legislation on
the maintenance of “greenness” in synthetic pathways and processes. Green chemistry
strongly influences chemical research, and there is an insistence on the use of “greener”
reaction conditions.[5] Indeed, the use of ILs, as a green solvents, in organic reactions
has improved not only the aspect of the reactions from the viewpoint of green and sus-
tainable properties but also the synthetic efficiency by stabilizing the catalyst, changing
the reaction selectivity or facilitating product isolation.[6–14] Particularly, ILs, as a green
solvents, showed a great ability for multicomponent reaction (MCRs).[15] In contrast of
conventional multistep synthetic protocols, the MCRs using ILs deliver outstanding ben-
efits, such as simple experimental procedures, creation of several carbon–carbon and
carbon–heteroatom bonds in a single operation, high atom economy, high yields, less
formation of by products, short reaction times, and restraint of complex isolation and
purification of intermediates.[16]
Pyrroles are one of the major classes of heterocyclic compounds, having increasing
importance in medicinal chemistry and organic synthesis. Several pyrroles as core
structures are found in natural products, bioactive compounds, drug molecules, and
optoelectronic materials. The pyrroles structural motifs have shown a wide range of
biological properties such as antibacterial,[17] antioxidant,[18] anti-inflammatory,[19]
antifungal agents,[20] and antitumor.[21] In addition, they are used as a chromophores
in an electro-optic (EO) devices. Recently Nishihara et al. showed pyrroles based
p-conjugated system as a candidates for molecular flat-band ferromagnets.[22] The
pyrroles derivatives have significant importance in the pharmaceutical industry and
the synthesis of these novel type of heterocycles desirable. Numerous elegant
approaches have been developed to access for the pyrroles derivatives. These include
traditional methods such as classical Knorr reaction, the Hantzsch reaction, and the
Paal ꢁ Knorr condensation reaction, multicomponent coupling, tandem reactions,
transition-metal-catalyzed cyclization, and catalytic C–H bond functionalization
strategies.[23]
Until now, a three-component reaction of amines, aldehydes, and b-nitrostyrene is
reported to give tetrasubstituted pyrroles derivatives using FeCl3 as a transition metal
catalyst.[24] But unfortunately, the tetrasubstituted pyrroles derivatives has basically been
catalyzed by transition metals or carried out in toxic solvents whose uses have been lim-
ited from its noncompliance with the requirements of green chemistry. Thus, the search
for green solvent as well as convenient catalyst is desirable. In continuation of our
ongoing research to development of greener methods for the synthesis interesting bio-
logically active heterocycles,[25–28] we disclose herein for the first time a greener method
one-pot multicomponent synthesis of tetrasubstituted pyrroles derivatives using imida-
zolium Brønsted acidic ionic liquid (Scheme 1).
Balu Atar, Amol
