Abstract:
Multicomponent reactions (MCRs),
a significant subclass of reac
tions, are one-pot processes
in which three or four easily-approachable components react to form a single product. The
methodology is a powerful synthetic tool for the preparation of important drugs and other
biologically active compounds.
1
MCRs have been useful in the development of environ-
mentally-friendly and less expensive procedure
s for the generation of libraries of heterocy-
clic compounds
2
and the development of MCRs can le
ad to new, efficient, synthetic
methodologies. Tetrahydrobenzo[b]pyrans an
d their derivatives are an important class of
heterocyclic compounds with antic
oagulant, antitumor, spasmoly
tic, antibacterial, diuretic,
potassium channel activating and
insulin-sensitizing activities.
3–6
4H-Benzo[b]pyrans are
usually synthesized from
a
-cyano cinnamonitrile derivatives with dimedone catalyzed by
acid or base.
7
Recently MCRs have been used for their preparation. As compared to the
conventional linear step synthesis, they can make the process easier, reduce time, save
money, energy, and raw materials, resulting in both economic and environmental bene-
fits.
8–9
A number of methods have been reported using dimedone, aromatic aldehydes and
malononitrile in the presence of catalysts, such as CeCl
3
¢
7H
2
O,
10
N-methylimidazole,
11
tet-
ramethyl ammonium hydroxide,
12
MgO,
13
amines,
14
2,2,2-trifluoroethanol,
15
and TiO
2
.
16
Other methods have involved microwave heating,
17
ultrasonic irradiation,
18
electrosynthe-
sis,
19
hexadecyldimethylbenzylammonium bromide (HDMBAB),
20
Na
2
SeO
4
,
21
DABCO,
22
