Highly Efficient and Single Step Synthesis of 4-Phenylcoumarins and 3,4-Dihydro-4-phenylcoumarins over Montmorillonite K-10 Clay, under Microwave Irradiation

Article abstract of DOI:10.1039/a708103k

A simple, elegant and one-pot synthesis of 3,4-dihydro-4-phenylcoumarins, 4-phenylcoumarins and their derivatives by making use of solid support, montmorillonite K-10 clay in conjunction with microwave irradiation is described.

Full text of DOI:10.1039/a708103k

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280 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 280±281$
Highly Efficient and Single Step Synthesis of
4-Phenylcoumarins and 3,4-Dihydro-4-
phenylcoumarins Over Montmorillonite K-10 Clay,
Under Microwave Irradiation$
Jasvinder Singh,* Jasamrit Kaur, Sandeep Nayyar and
Goverdhan L. Kad
Department of Chemistry, Panjab University, Chandigarh-160 014, India
A simple, elegant and one-pot synthesis of 3,4-dihydro-4-phenylcoumarins, 4-phenylcoumarins and their derivatives by
making use of solid support, montmorillonite K-10 clay in conjunction with microwave irradiation is described.
Coumarins and dihydrocoumarins are an important class of
organic compounds, used in the pharmaceutical industry
and as intermediates in the synthesis of useful pesticides and
bioactive compounds. A number of syntheses of coumarins
are available which o€er a variety of intermediates and
reaction conditions.1±7 Some of the problems which arise
with these have been avoided by employing solid supports
under microwave conditions.8±10
We have found that some 3,4-dihydro-4-phenylcoumarins
and 4-phenylcoumarins can be obtained in a single step and
in good yield. Phenol (or its derivatives) and cinnamic
Scheme 1
acid (or its derivatives) impregnated on activated mont-
morillonite K-10 clay (by heating under vacuum for 2 h),
when subjected to microwave irradiation (MWI), in an
open vessel and employing optimized conditions of 640 W
power output in a domestic microwave oven, for 8±10 min,
furnished 3,4-dihydro-4-phenylcoumarin and its derivatives
1±5, Scheme 1. The results of this reaction are summarized
in Table 1.
The methodology adopted has a few advantages (i) no
solvent is required and (ii) since an open vessel is used there
is no question of excessive accumulation and consequent
danger of explosion. The exact role of the microwave
radiation is not known, that is whether it provides a thermal
e€ect or in some way decreases the activation barrier, so that
the reaction proceeds quickly. Montmorillonite KSF-clay
predoped with or without ZnCl2 was also used, however
Table 1 Reaction between phenols and cinnamic acids to form 3,4-dihydro-4-phenylcoumarins
13C NMR
300 MHz
1H NMR
(d)
Mass
spectrum
m/z M /% 8C
Solid
support
Yield (d)/phase
Mp (lit.)/
1
‡
Compound
R
H
R'
t/min (%)
on DEPT
ꢀ
max/cm
1
p-OMe
K-10
8
85
167.827/
37.21/ ve
2.94±3.09
(m, 2 H)
4.28±4.32
(t, 1 H)
1760, 1160, 254/100
1240
98a
39.90/ ‡ ve 3.79 (s, 3 H)
2
m-OH
H
H
KSF/ZnCl2 20
(no acid)
79
167.001/
2.83±3.00
(m, 2 H)
4.06±4.24
(t, 1 H)
1760, 1210, 240/24
3200±3400
140±142
(1401)
36.54/ ve
38.93/ ‡ ve 6.45 (br s, OH)
K-10
K-10
8
8
75
81
38.93/ ‡ ve 6.45 (br s, OH)
240/22
3
4
5
m-OMe
167.741/
2.96±3.10
(m, 2 H)
1760, 1130, 254/100
1220
110±114
(1121)
37.404/ ve 4.26±4.31
(t, 1 H)
40.192/ ‡ ve 3.80 (s, 3 H)
H
H
m,p-OCH2O- K-10
10
65
167.683/
2.94±3.09
(m,2 H)
1770, 1230, 268/100
1260
118b
37.32/ ve
4.25±4.29
(t, 1 H)
39.89/ ‡ ve 5.95 (s, 2 H)
167.645/ 2.98±3.13
(m, 2 H)
37.063/ ve 4.32±4.37
(t,1 H)
H
K-10
10
22
82
74
1780, 1140, 224/65
1240
80±82
(831)
KSF
(no acid)
40.749/ ‡ ve
aFound: C, 75.43; H, 5.59. C16H14O3 requires C, 75.58; H, 5.55%. bFound: C, 71.69; H, 4.55. C16H12O4 requires C, 71.64; H, 4.51%.
greater exposure time to MWI was required. When a mix-
ture of phenol, cinnamic acid and one drop of H2SO4 was
re¯uxed in dimethylformamide for 10 h, with or without
K-10 clay, no reaction was observed.
*To receive any correspondence.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

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J. CHEM. RESEARCH (S), 1998 281
Table 2 Reactions of phenols and phenylpropynoic acid to form coumarins
Main peak in
300 MHz
Mass
spectrum
m/z M /% 8C
Yield
(%)
Mp (lit.)/
1
‡
Compound
R0
R000
t/min
1H NMR (d)
ꢀmax/cm
6
7
8
H
m-OMe
H
H
10
10
10
69.5
55.0
67.0
6.42 (s, 1 H)
6.28 (s, 1 H)
6.20 (s, 1 H)
1710, 1620, 1240
1700, 1630, 1220
1690, 1620, 1260
222/60
252/54
252/46
102±104(10513
)
H
p-OMe
138a
101±103b
aFound: C, 76.29, H, 4.51. C16H12O3 requires C, 76.18; H, 4.79%. bFound: C, 76.06, H, 4.70. C16H12O3 requires C, 76.17; H, 4.77%.
NaHCO3 solution, brine and dried over Na2SO4. Evaporation of
the solvent in vacuo yielded the product, 1.05 g (82%). 1H NMR
(300 MHz, CDCl3): ꢁ 7.29±7.26 (d, J ˆ 4, 1 H), 7.11±7.08 (t, J ˆ 4,
4 H), 6.99±6.97 (d, J ˆ 4, 1 H), 6.89±6.86 (d, J ˆ 4, 2 H), 4.32±4.28
(t, J ˆ 6 Hz, 1 H), 3.79 (s, 3 H) and 3.09±2.94 (m, 2 H). Mass
Similarly, when phenol (or its derivatives) and phenyl-
propynoic acid (or its derivatives) were subjected to MWI
in the presence of montmorillonite K-10 clay with one drop
of H2SO4 and placed in a silica bath, coumarins 6±8
(Scheme 2) were obtained in good yield as shown in Table 2.
‡
‡
spectrum (m/z, % base): 255/24 (M ‡1), 254/100 (M ), 253/5
‡
(M 1), 149/4 and 148/17. 13C NMR (CDCl3/phase on DEPT):
ꢁ 167.827, 159.005, 151.681, 132.240, 128.643/‡ve, 128.310/‡ve,
126.250, 124.659/‡ve, 117.097/‡ve, 114.502/‡ve, 55.320/‡ve,
39.900/‡ve and 37.210/ ve. IR (CCl4, cm 1): 1760, 1240, 1160
and 750±710.
We are grateful to the CSIR, New Delhi, for providing
®nancial assistance for this work.
Received, 11th November 1997; Accepted, 27th January 1998
Paper E/7/08103K
Scheme 2
References
The results of the spectral data were compared with the
data for analogs or similar systems.11 The most relevant
resonance in the 13C NMR spectrum is at d 167±168, corre-
sponding to the carbonyl carbon. Condensation reactions
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Experimental
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Montmorillonite K-10 clay was purchased from Fluka.
Typical Procedure.ÐTo activated montmorillonite K-10 clay (2 g)
in a 100 ml Erlenmeyer ¯ask was added a mixture of freshly distilled
phenol (0.50 g, 5.3 mmol) and recrystallized p-methoxycinnamic
acid (0.94 g, 5.3 mmol) dissolved in CH2Cl2 (5 ml) along with one
drop of concentrated H2SO4. The solvent was evaporated and the
resultant free-¯owing solid placed on a silica bath and subjected
to MWI at 640 W for 10 min. Dichloromethane (20 ml) was added,
the reaction mixture ®ltered and the ®ltrate washed with saturated
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