Bi(NO3)3Al2O3-mediated efficient synthesis of 4-aryl-2,6-dicoumarinylpyridines under solventless conditions

Article abstract of DOI:10.1071/CH07206

A new efficient and eco-friendly methodology has been developed for the synthesis of 4-aryl-2,6-dicoumarinylpyridines from coumarinylchalcones and urea, using Bi(iii) nitrate?Al₂O₃ as catalyst. Coumarinylchalcones were in turn prepar

Full text of DOI:10.1071/CH07206

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2007, 60, 883–888
Bi(NO3)3–Al2O3-Mediated Efficient Synthesis
of 4-Aryl-2,6-dicoumarinylpyridines Under
Solventless Conditions
Anil K. Verma,A Summon Koul,A,B Kamal K. Kapoor,A and Tej K. RazdanA,C
ADepartment of Chemistry, University of Jammu, Ambedkar Road, Jammu-180 006, India.
BPresent address: Department of Chemistry, British Columbia University, Canada.
CCorresponding author. Email: tk_razdan@rediffmail.com
A new efficient and eco-friendly methodology has been developed for the synthesis of 4-aryl-2,6-dicoumarinylpyridines
from coumarinylchalcones and urea, using Bi(iii) nitrate–Al2O3 as catalyst. Coumarinylchalcones were in turn prepared
from salicylaldehyde and ethylacetoacetate by the tandem reaction with aldehydes on the surface of Bi(iii) nitrate–Al2O3
in the presence of the co-catalyst Zn(ii) chloride.
Manuscript received: 16 June 2007.
Final version: 7 September 2007.
Introduction
report the preparation of 4-aryl-2,6-dicoumarinylpyridines from
coumarinylchalcones using the same reagents, under solventless
conditions.
Coumarins are well documented for their photosensitizing[1]
and a wide range of other biological activities.[2] They also
find industrial[3] and analytical applications.[4] Their 3- and
4-heteroaryl derivatives are associated with monoamine reduc-
tase inhibiting activity,[5] and bactericidal,[6] fungicidal,[7] and
CNS-depressant activities.[8] For obvious reasons, the synthe-
sis of pyridylcoumarins has gained considerable attention.[9]
Symmetrically substituted triarylpyridines too are pharmaco-
logically potent compounds.[10] These products also display
photodynamic activity[11] and show fluorescence and scintil-
lation properties.[12] Moreover, these products are structurally
related to the photodynamic 2,4,6-triaryl-selenopyrylium,
-telluropyrylium, and -thiopyrylium cell-specific cancer thera-
peutic agents.[11] We envisaged that, by virtue of their syner-
gistic photodynamic activity, the suitably substituted pyridine
derivatives bearing one or more coumarin pharmacophores
might prove pharmacodynamically more efficacious than the
aforementioned products and might avoid the metal toxicity.
Traditionally, coumarin derivatives are synthesized by the Pech-
man condensation,[13] Knoevenagel’s reaction,[14] or the Wittig
reaction[15] or their modified versions involving Lewis acids[16]
or cation-exchange resins.[17] However, these methodologies fail
to bring about the substitutions in the pyridine nucleus.Although
several approaches to the synthesis of triarylpyridines have
emerged,[18] these products are mostly prepared by Krohnke[19]
or modified Krohnke synthesis.[20]
Results and Discussion
Our protocol for the synthesis of 4-aryl-2,6-dicoumarinyl-
pyridines consisted of 3-acetylcoumarin, an aldehyde, urea, and
Bi(iii) nitrate immobilized on alumina. As we have been inter-
ested in exploring the catalytic efficiency of the readily available
non-toxic, air- and moisture-resistant Bi(iii) nitrate immobilized
on neutral alumina, in the synthesis of heterocyclic products,
we first prepared 3-acetylcoumarin by heating an equimolar
mixture of salicylaldehyde and ethylacetoacetate on the sur-
face of 5% w/w Bi(iii) nitrate–Al2O3 in the absence of solvent.
3-Acetylcoumarin was obtained but in low yield and the reac-
tion proceeded with the formation of a multicomponent mixture.
Therefore, it occurred to us that the use of a co-catalyst might
help in arresting the side reactions.As our primary goal has been
to make use of biocompatible metal salts as catalysts, we chose
Zn(ii) chloride as a co-catalyst in the cycloaddition reaction of
salicylaldehyde. After several experiments for optimization, the
optimum concentration of Zn(ii) chloride, as the co-catalyst, was
found to be 2.5% w/w. 3-Acetylcoumarin 3[17] was obtained in
85% yield (Scheme 1).
Next, we attempted further condensation of the
3-acetylcoumarin with the aromatic aldehydes, using the mod-
ified bismuth(iii) nitrate–Al2O3–ZnCl2 catalyst. The reaction
mixture was heated at 120 5◦C, in a hot-air oven, for 4–5 h,
when coumarinylchalcones 5a–g (Scheme 2) were obtained in
65–75% yield (Table 1). Encouraged by these observations, we
conducted the tandem reactions of salicylaldehyde, ethylaceto-
acetate, and aldehydes 4a–g on the surface of bismuth(iii)
nitrate–Al2O3–ZnCl2 (5%, 2.5% w/w) catalyst, at a temperature
of 120 5◦C. The coumarinylchalcones were obtained in nearly
the same percentage yield as in the two-stage reaction. Although
the exact role of the co-catalyst zinc(ii) chloride in the presence
In both cases, although improvements in the percentage yield
of the products has been registered, each synthesis is compli-
cated by one or more drawbacks, such as the involvement of
multistage laborious processes, stringent and environmentally
hazardous reaction conditions, the use of expensive rare-earth
Lewis acids and their substrate selectivity, and the require-
ment of stoichiometric amount of reagents. Recently,[21] we
observed that Bi(iii) nitrate, immobilized on Al2O3, efficiently
convertedchalconesandureainto2,4,6-triarylpyridines.Wenow
© CSIRO 2007
10.1071/CH07206
0004-9425/07/110883

884
A. K. Verma et al.
of bismuth(iii) nitrate in the reaction is not understood, the
formation of 3-acetylcoumarin may involve a Mukaiyama-type
aldolcondensationofsalicylaldehydewithethylacetoacetatefol-
lowed by cyclization. The 3-acetylcoumarin may then undergo
further aldol condensation with the aldehydes (Fig. 1) to give
5a–g.
In the next step, the coumarinylchalcones and urea (2:1 mol
ratio), in chloroform solution, were adsorbed on 5% w/w Bi(iii)
nitrate–Al2O3 catalyst (Scheme 3). After the mixture was dried
in air, the reaction mixture was heated at 120 5◦C in a thermo-
statically controlled hot-air oven. On completion of the reaction
(5–6 h), as evidenced from the TLC of the aliquots drawn out
at 0.5-h intervals from a simultaneously run separate experi-
ment, the products 7a–g were extracted with hot chloroform
and were purified by column chromatography on silica gel, using
petroleum spirits (bp 40–60◦C)/benzene graded solvent systems.
The products 7a–g were obtained in 65–75% yield (Table 2)
and were characterized as 4-aryl-2,6-dicoumarinylpyridines by
spectroscopic methods (HREIMS, IR, 1H NMR, 13C NMR,
DEPT 135◦).
(Scheme 3).These reaction also yielded minor quantities of alde-
hydes from which the chalcones were initially prepared. The
percentage yield of the 4-aryl-2,6-dicoumarinylpyridines thus
obtained are given in Table 2.
Mechanistically, the reaction seems to follow the path-
way involving the homomolecular Michael addition of two
coumarinylchalconesfollowedbytheheteroannulationwithurea
and simultaneous retro-aldol disproportionation. Subsequent
dehydration and catalytic oxidation may lead to the forma-
tion of the pyridinium ion, which on hydrolysis may afford
4-aryl-2,6-dicoumarinylpyridines (Fig. 2).[21]
Conclusions
We have thus developed a simple two-stage straightforward, eco-
friendly and efficient procedure for the synthesis of coumarins,
coumarinylchalcones, and 4-aryl-2,6-dicoumarinylpyridines,
using for the first time the biocompatible immobilized bis-
muth(iii) nitrate as a catalyst in the presence and absence of
the co-catalyst zinc(ii) chloride. This procedure has an added
advantage that the catalysts are non-toxic and biocompatible.
Further work on the use of these catalysts in the preparation of
bioactive heterocyclic compounds is in progress.
All these reactions afforded minor quantities of the aldehydes
from which the coumarinylchalcones were initially prepared.
The IR spectra of the compounds showed absorption bands
at νmax 3000–2990, 1723–1736, 1620, 1600, and 1450 cm−1
.
Experimental
The 1H NMR spectra of the compounds displayed characteristic
resonance signals at δ 7.20–7.30 (s, 2H), due to the protons of
the pyridine ring. The 13C NMR spectrum exhibited the char-
acteristic resonance signals at δ 91.8, 112, 115.9, 129.3, 151.9,
160.7–161.5.
Melting points are uncorrected and were determined on Per-
fit melting point apparatus. IR spectra were recorded from
KBr disks. 1H NMR, 13C NMR, and DEPT 135◦ spectra were
recorded on a 200 MHz Bruker AcDPX-200 spectrometer, and
chemical shifts were determined from expanded peak segregated
graphs. HREIMS was recorded at 70 eV. TLC was performed on
0.5-mm thick plates using silica gel G adsorbent. Column chro-
matography was performed on silica gel (60–120 mesh) using
graded solvent systems of petroleum spirits (bp 40–60◦C) and
benzene (9:1; 7:3; 3:7; 1:9 v/v). The products were crystallized
from chloroform/petroleum spirits (bp 40–60◦C).
In order to generalize this reaction, we carried out the reac-
tions of coumarinylchalcones 5a–c with acetamide 6b, benza-
mide 6c and thiourea 6d, using the aforementioned procedure
R1
R2
O
Two steps
O
CH3
ꢀ
Table 1. Percentage yield of coumarinylchalcones 5a–g
OEt
OH
N
O
O
O
O
O
Product
% yield (stepwise)
% yield (tandem)
O
5a
5b
5c
5d
5e
5f
65
75
70
72
71
73
69
64
73
71
70
70
72
68
O
CH3
OEt
(i) Bi(III)–Al2O3–Zn(II) chloride
O
CH3
ꢀ
120 ꢁ 5°C, ∆
OH
O
3
O
O
2
(85%)
1
Scheme 1. Preparation of 3-acetylcoumarin from salicylaldehyde and
ethylacetoacetate in the solid state.
5g
O
O
O
CH3
R2
R1
Bi(III)–Al2O3–Zn(II) chloride
H
ꢀ
120 ꢁ 5°C, ∆
R1
O
O
O
O
R2
5a–g
3
4a–g
4a: R1 ꢂ R2 ꢂ H
4b: R1 ꢂ OCH3; R2 ꢂ H
4c: R1 ꢂ Cl; R2 ꢂ H
4d: R1 ꢂ Br; R2 ꢂ H
4e: R1 ꢂ R2 ꢂ Cl
4f: R1 ꢂ R2 ꢂ Br
4g: R1 ꢂ R2 ꢂ ꢃOCH2Oꢃ
Scheme 2. Coumarinylchalcones 5a–g from 3-acetylcoumarin and substituted aromatic aldehydes.

Synthesis of 4-Aryl-2,6-dicoumarinylpyridines
885
Preparation of Catalyst
aliquots drawn out from a simultaneously run separate exper-
imental flask, under identical reaction conditions. The reaction
was complete in 30 min. On completion of the reaction, the
product was extracted with chloroform and recrystallized from
ethanol.
Bismuth(iii) nitrate (2.5 g) in 50% methanol (100 mL) was added
to neutral alumina (50 g) and the mixture was stirred at room
temperature for 12 h. The mixture was air-dried and then heated
at 110 5◦C, in a thermostatic hot-air oven, for 6 h. In the second
case, the catalyst 5% w/w bismuth(iii) nitrate, prepared as above,
was treated with zinc(ii) chloride (1.25 g) in CHCl3 (100 mL),
and the mixture was stirred for 4 h. The solvent was removed
under pressure. The mixture was reactivated at 110 5◦C for
4 h. The activated bismuth(iii) nitrate–zinc(ii) chloride–Al2O3
mixture was cooled in a dessicator and preserved. The catalyst
was reactivated at 110 5◦C for 0.5 h each time before use.
Table 2. Percentage yield of coumarinylpyridines with
amino derivatives
Product
Yield with different amino compounds
6a
6b
6c
6d
7a
7b
7c
7d
7e
7f
70
75
68
65
69
71
67
67
71
64
–
–
–
65
74
64
–
–
–
68
73
67
–
–
–
General Procedure for the Synthesis of 3-Acetylcoumarins
Salicylaldehyde (1 mol) and ethylacetoacetate (1 mol) were
adsorbedonthebismuth(iii)nitrate–zinc(ii)chloride–Al2O3 cat-
alyst in proportion by weight of the substrates. The mixture was
dried in air and heated at 120 5◦C in a thermostatically con-
trolled hot-air oven. The reaction was monitored by TLC of
7g
–
–
–
OH
O
Cat.
O
O
O
H
Cat.
O
O
H
Bi(NO3)3–Al2O3–ZnCl2
H
O
OEt
CH3
Cat.
O
EtO
O:
H
OEt
Cat.
O
O
O
O
O
O
Cat.
H
O
Cat.
O
O
O
OEt
O
H
ꢃCat.Hꢀ
R1
R2
O
R1
O
O
R2
Fig. 1. Probable mechanism for the formation of 3-acetylcoumarin and coumarinylchalcones.
R1
R2
O
X
Bi(III) nitrate–Al2O3
ꢀ
R1
NH2
R3
120 ꢁ 5°C, ∆
O
O
N
6a–d
R2
5a–g
O
O
O
O
5a: R1 ꢂ R2 ꢂ H
6a: X ꢂ O; R3 ꢂ NH2
6b: X ꢂ O; R3 ꢂ CH3
6c: X ꢂ O; R3 ꢂ C6H5
6d: X ꢂ S; R3 ꢂ NH2
7a–g
5b: R1 ꢂ OCH3; R2 ꢂ H
5c: R1 ꢂ Cl; R2 ꢂ H
5d: R1 ꢂ Br; R2 ꢂ H
5e: R1 ꢂ R2 ꢂ Cl
5f: R1 ꢂ R2 ꢂ Br
5g: R1 ꢂ R2 ꢂ ꢃOCH2Oꢃ
Scheme 3. 4-Aryl-2,6-dicoumarinylpyridines from coumarinylchalcones and urea derivatives.

886
A. K. Verma et al.
Cat.
O
R2
O
R1
R2
Cat.
X
R3
NH2
R1
O
Coum.
R2
Bi(III)–Al2O3
Coum.
120 ꢀ 5°C, ∆
ꢀ
Cat.
Coum.
R1
O
Michael-addition
Cat.
R2
Cat.
O
R2
Coum.
R1
R1
O
Coum.
X
R1
R1
Condensation
N
R3
O
O
O
Coum.
Cat.
R2
Coum.
R2
Heteroannulation and
retro-aldol
R1
R1
R1
R2
R2
R2
H
O
H
1. ꢃH2O
2. Oxidation
ꢀ
Hydrolysis
H
..
R2
HO
Coum.
Coum.
N
Coum.
N
Coum.
Coum.
N
Coum.
R1
X
R3
X
R3
Coum. ꢂ
O
O
Fig. 2. Probable mechanism of the formation of 4-aryl-2,6-dicoumarinylpyridines.
General Procedure for the Synthesis of
Coumarinylchalcones 5a–g
conditions as described above. To this mixture, the appropriate
aromatic aldehyde (1 mol) was added and the mixture was again
heated for 4–5 h. The resulting products were isolated by the
same procedure as described above and were confirmed by mp
and mixed mp with the products formed in the stepwise reaction.
A mixture of 3-acetylcoumarin and appropriate benzaldehyde
4a–g (1:1 mol ratio) were absorbed on Bi(iii) nitrate–Al2O3–
ZnCl2, in proportion by weight of the substrates. The mixture
was thoroughly mixed and charged into a stoppered flask. The
flask was heated at 120 5◦C in a thermostatically controlled
hot-air oven. Separate experiments were run, simultaneously,
to monitor the reaction by comparative TLC of the chloroform
extracts of the aliquots, drawn out from reaction flask at 0.5-h
intervals, using pet. ether/benzene (7:3; 1:1 v/v) graded sol-
vent systems. The plates were developed first by exposure to
iodine vapour followed by spraying with Ceiv ions, when the
products were observed as pink spots. On completion of the
reaction (4–5 h), the products were extracted with chloroform in
a Soxhlet extractor. The solvent was distilled off. The products
were purified by column chromatography, using petroleum spir-
its (bp 40–60◦C)/C6H6 graded solvent systems and finally by
crystallization from chloroform/petroleum spirits.
General Procedure for the Synthesis of 7a–g
Coumarinylchalcones 5a–g (2 mmol) and the substrate carrying
the terminal amino group viz. urea 6a, acetamide 6b, benzamide
6c, and thiourea 6d (1 mmol) in 10 mL chloroform solution were
adsorbed on the surface of the catalyst Bi(iii) nitrate–Al2O3 in
proportion by weight of the substrates. The solvent was evapo-
rated in air and the air-dried mixture was charged in a stoppered
flask. The flask was then heated at 120 5◦C in a thermo-
statically controlled hot-air oven. The reaction was monitored
by comparative TLC of the chloroform extracts of the aliquots
drawn out at 0.5-h intervals from the reaction flask (petroleum
spirits (bp 40–60◦C)/C6H6 (19:1 and 3:7 v/v) were used as a
graded solvent system for TLC). The plates were developed first
by exposure to iodine vapour followed by spraying with Ce(iv)
ions, when dark blue spots against a pale white background were
observed. On completion of the reaction (5–6 h), the products
were extracted with CHCl3 in a Soxhlet extractor, freed from
the solvent, and purified by column chromatography, by using
the petroleum spirits (bp 40–60◦C)/C6H6 graded solvent system
General Procedure for the Tandem Reactions
for the Preparation of 5a–g
A mixture of salicylaldehyde (1 mol) and ethylacetoacetate
(1 mol) were adsorbed on the catalyst by weight of the sub-
strates. The mixture was heated in a hot-air oven, under the same

Synthesis of 4-Aryl-2,6-dicoumarinylpyridines
887
described above, and finally crystallized from CHCl3/petroleum
spirits (bp 40–60◦C).
730 cm−1. δH (CDCl3, 200 MHz) 7.19 (s, 1H, H6ꢀꢀ), 7.26 (d, 1H,
J 8.0, H3ꢀꢀ), 7.32 (dd, J 8.0, 3.2, 2H, H5ꢀ, H5ꢀꢀꢀ), 7.38 (s, 2H,
H3, H5), 7.50 (dd, J 8.0, 3.2, 4H, H6ꢀ, H6ꢀꢀꢀ, H7ꢀ, H7ꢀꢀꢀ), 8.09
(dd, J 8.0, 3.2, 2H, H8ꢀ, H8ꢀꢀꢀ), 8.18 (d, J 8.0, 1H, H2ꢀꢀ), 8.78 (s,
2H, H4ꢀ, H4ꢀꢀꢀ). δC (CDCl3) 91.6 (C3ꢀ), 110.3 (C4ꢀꢀ), 112.8 (C4),
113.4 (C4aꢀ), 116.8 (C6ꢀꢀ), 117.4 (C8ꢀ), 122.9 (C5ꢀ), 125.3 (C5ꢀꢀ),
125.6 (C6ꢀ), 125.7 (C3ꢀꢀ), 127.1 (C2ꢀꢀ), 129.1 (C3), 132.5 (C7ꢀ),
136.5 (C1ꢀꢀ), 152.6 (C6), 153.1 (C8aꢀ), 154.2 (C2), 161.5 (C2ꢀ).
m/z 511.0270 (calc. for C29H15Cl2NO4: 511.0320, 515.0320),
484, 456, 364, 272, 224, 79.
Spectroscopic Data for Compounds
4-Aryl-2,6-dicoumarinylpyridine 7a
Colourless crystals (0.620 g), mp 165◦C. νmax 3000, 1730,
1716, 1610, 1495, 1450, 1395, 1278, 1210, 1050, 999, 876 cm−1
.
δH (200 MHz, CDCl3) 6.80 (dd, J 8.02, 2.3, 4H, H5ꢀ, H7ꢀ, H5ꢀꢀꢀ,
H7ꢀꢀꢀ), 7.12–7.26 (m, 5H, ArH), 7.46 (d, J 1.8, 2H, H3, H5), 7.56
(dd, J 8.0, 2.1, 2H, H6ꢀ, H6ꢀꢀꢀ), 8.17 (dd, J 8.1, 2.3, 2H, H8ꢀ,
H8ꢀꢀꢀ), 8.88 (s, 2H, H4ꢀ, H4ꢀꢀꢀ). δC (CDCl3) 91.2 (C3ꢀ), 113.1
(C4aꢀ), 114.5 (C3ꢀꢀ, C5ꢀꢀ), 115.3 (C4), 117.8 (C8a), 119.8 (C5),
122.4 (C4ꢀ), 122.5 (C5ꢀ), 122.8 (C1ꢀꢀ), 125.0 (C6ꢀ), 130.7 (C2ꢀꢀ,
C6ꢀꢀ), 132.5 (C7ꢀ), 136.8 (C4ꢀꢀ), 153.1 (C8aꢀ), 154.0 (C2, C6),
161.2 (C2ꢀ). m/z 443.1153(calc. for C29H17NO4: 443.1158) 415,
387, 295, 203, 155, 79.
4-(3,4-Dibromophenyl)-2,6-dicoumarinylpyridine 7f
Colourless needles (0.850 g), mp 190◦C. νmax 3020, 1605,
1545, 1490, 1385, 1350, 1142, 1096, 920, 700 cm−1. δH
(200 MHz, CDCl3) 7.19 (s, 1H, H6ꢀꢀ), 7.20 (d, J 8.0, 1H, H3ꢀꢀ),
7.33 (dd, J 8.0, 3.2, 2H, H5ꢀ, H5ꢀꢀꢀ), 7.36 (s, 2H, H3, H5), 7.50 (dd,
J 8.0, 3.2, 4H, H6ꢀ, H6ꢀꢀꢀ, H7ꢀ, H7ꢀꢀꢀ), 7.80 (d, J 8.0, 1H, H2ꢀꢀ),
8.09 (dd, J 8.0, 3.2, 2H, H8ꢀ, H8ꢀꢀꢀ), 8.80 (s, 2H, H4ꢀ, H4ꢀꢀꢀ).
δC (CDCl3) 91.6 (C3ꢀ), 113.4 (C4aꢀ), 116.7 (C4ꢀꢀ), 117.4 (C8ꢀ),
117.8 (C4), 119.8 (C3ꢀꢀ), 120.4 (C5), 122.9 (C5ꢀ), 125.6 (C6ꢀ),
126.7 (C5ꢀꢀ), 129.1 (C3), 130.5 (C1ꢀꢀ), 132.5 (C7ꢀ), 135.5 (C6ꢀꢀ),
138.7 (C4ꢀ), 144.2 (C2ꢀꢀ), 152.6 (C6), 153.1 (C8aꢀ), 154.1 (C2),
161.1 (C2ꢀ). m/z 599.0564 (calc. for C29H15Br2NO4: 599.0569,
602.9329), 573, 545, 453, 361, 313, 79.
4-(4-Methoxyphenyl)-2,6-dicoumarinylpyridine 7b
Colourless crystals (0.709 g), mp 180◦C. νmax 3020, 1730,
1716, 1606, 1550, 1495, 1420, 1359, 1157, 1028, 1010, 990,
870, 755 cm−1. δH (200 MHz, CDCl3) 3.80 (s, 3H, OCH3), 6.89
(dd, J 8.0, 2.3, 4H, H5ꢀ, H7ꢀ, H5ꢀꢀꢀ, H7ꢀꢀꢀ), 6.95 (dd, J 8.1, 2H,
H3ꢀꢀ, H5ꢀꢀ), 7.48 (s, J 2.3, 2H, H3, H5), 7.56 (dd, J 8.0, 2.1,
2H, H6ꢀ, H6ꢀꢀꢀ), 7.69 (dd, J 8.1, 2.3, 2H, H2ꢀꢀ, H6ꢀꢀ), 8.19 (dd,
J 8.1, 2.3, 2H, H8ꢀ, H8ꢀꢀꢀ), 8.88 (s, 2H, H4ꢀ, H4ꢀꢀꢀ). δC (CDCl3)
55.10 (OCH3), 91.80 (C3ꢀ), 113.1 (C4aꢀ), 114.8 (C3ꢀꢀ, C5ꢀꢀ),
112.3 (C4), 117.8 (C8aꢀ), 119.8 (C3, C5), 122.7 (C5ꢀ), 125.3
(C6ꢀ), 130.9 (C2ꢀꢀ, C6ꢀꢀ), 130.0 (C1ꢀꢀ), 138.9 (C4ꢀ), 132.5 (C7ꢀ),
153.1 (C8aꢀ), 154.0 (C2, C6), 161.3 (C2ꢀ). m/z 473.1260 (calc.
for C30H19NO5: 473.1264) 445, 417, 325, 233, 185, 79.
4-(3,4-Dioxymethylenephenyl)-
2,6-dicoumarinylpyridine 7g
Colourless crystals (0.652 g), mp 195◦C. νmax 3056, 1730,
1710, 1610, 1549, 1450, 1385, 1350, 1260, 1096, 1050, 980, 926,
765 cm−1. δH (200 MHz, CDCl3) 6.01 (s, 2H, OCH2O), 6.90 (s,
1H, H2ꢀꢀ), 7.26 (d, J 8.5, 3H, H3, H5, H3ꢀꢀ), 7.32 (dd, J 8.0, 3.2,
2H, H5ꢀ, H5ꢀꢀꢀ), 7.50 (dd, J 8.0, 3.2, 4H, H6ꢀ, H6ꢀꢀꢀ, H7ꢀ, H7ꢀꢀꢀ),
7.53 (dd, J 8.5, 3.2, 1H, H6ꢀꢀ), 8.09 (dd, J 8.0, 3.2, 2H, H8ꢀ, H8ꢀꢀꢀ),
8.86 (s, 2H, H4ꢀ, H4ꢀꢀꢀ). δC (CDCl3) 91.6 (C3ꢀ), 101.0 (OCH2O),
113.4 (C4aꢀ), 114.5 (C4), 117.4 (C8ꢀ), 119.8 (C5), 122.7 (C5ꢀ),
124.1 (C5ꢀꢀ), 125.3 (C2ꢀꢀ), 125.6 (C6ꢀ), 129.1 (C6ꢀꢀ), 132.5 (C7ꢀ),
133.1 (C8aꢀ), 138.5 (C4ꢀ), 139.4 (C1ꢀꢀ), 152.6 (C6), 154.2 (C2),
157.2 (C4ꢀꢀ), 157.3 (C3ꢀꢀ), 162.2 (C2). m/z 487.1043 (calc. for
C30H17NO6: 487.1050) 459, 431, 339, 247, 199, 79.
4-(4-Chlorophenyl)-2,6-dicoumarinylpyridine 7c
Colourless needles (0.648 g), mp 185◦C. νmax 3000, 1728,
1710, 1608, 1550, 1490, 1420, 1355, 1152, 1030, 1010, 980,
870, 755 cm−ꢀꢀꢀ1. δH (200 MHz, CDCl3) 6.89 (dd, J 8.0, 2.3, 4H,
H5ꢀ, H7ꢀ, H5 , H7ꢀꢀꢀ), 7.32 (s, 2H, H3, H5), 7.48 (dd, J 8.5, 3.2,
2H, H3ꢀꢀ, H5ꢀꢀ), 7.56 (dd, J 8.0, 2.3, 2H, H6ꢀ, H6ꢀꢀꢀ), 7.73 (dd,
J 8.1, 2.3, 2H, H2ꢀꢀ, H6ꢀꢀ), 8.12 (dd, J 8.5, 3.2, 2H, H8ꢀ, H8ꢀꢀꢀ),
8.13 (s, 2H, H4ꢀ, H4ꢀꢀꢀ). δC (CDCl3) 91.8 (C3ꢀ), 113.1 (C4aꢀ),
115.9 (C4), 116.8 (C4ꢀꢀ), 117.8 (C8ꢀ), 119.8 (C5), 122.7 (C5ꢀ),
125.3 (C6ꢀ), 128.2 (C3ꢀꢀ), 132.5 (C7ꢀ), 129.3 (C3), 133.9 (C2ꢀꢀ,
C6ꢀꢀ), 139.4 (C1ꢀꢀ), 152.8 (C6), 153.1 (C8aꢀ), 154.0 (C2). m/z
477.0730 (calc. for C29H16ClNO4: 477.0739, 479.0739), 449,
421, 329, 237, 189, 79.
Acknowledgements
The authors are thankful to Dr R. G. Bhat, I.I.Sc. Bangalore, India, and Dr
S. K. Date, National Chemical Laboratory, Pune, for spectral analysis.
4-(4-Bromophenyl)-2,6-dicoumarinylpyridine 7d
References
Colourless needles (0.677 g), mp 170◦C. νmax 2990, 1730,
1728, 1610, 1545, 490, 1387, 1359, 1227, 1072, 1018, 925,
720 cm−1. δH (CDCl3, 200 MHz) 7.19 (d, J 8.0, 2H, H3ꢀꢀ, H5ꢀꢀ),
7.30 (d, J 8.0, 2H, H5ꢀ, H5ꢀꢀꢀ), 7.24 (s, 2H, H3, H5), 7.59
(d, J 8.0, 2H, H2ꢀꢀ, H6ꢀꢀ), 7.50 (dd, J 8.0, 3.2, 4H, H6ꢀ, H7ꢀ,
H6ꢀꢀꢀ, H7ꢀꢀꢀ), 8.08 (dd, J 8.0, 3.2, 2H, H8ꢀ, H8ꢀꢀꢀ), 8.88 (s, 2H,
H4ꢀ, H4ꢀꢀꢀ). δC (CDCl3) 91.6 (C3ꢀ), 110.4 (C4ꢀꢀ), 113.2 (C4),
113.5 (C4aꢀ), 117.5 (C8ꢀ), 119.9 (C5), 122.9 (C5ꢀ), 125.6 (C6ꢀ),
126.3 (C3ꢀꢀ, C5ꢀꢀ), 129.8 (C3), 132.7 (C7ꢀ), 137.8 (C1ꢀꢀ), 138.7
(C4ꢀ), 152.6 (C6), 153.1 (C8aꢀ), 161.5 (C2ꢀ). m/z 521.0856 (calc.
for C29H16BrNO4: 521.0863, 523.0243), 494, 466, 374, 282,
234, 79.
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