Synthesis and characterization of some chalcones and their cyclohexenone derivatives

Article abstract of DOI:10.2478/s11532-009-0124-x

A series of chalcones and their derivatives have been synthesized. Chalcones, 1-(1,3-benzodioxol-5-yl)-3-(aryl)-prop-2-en-1-ones were prepared by the aldol condensation of 1-(1,3-benzodioxol-5-yl)ethanones and aryl aldehydes. Based-catalyzed condensation

Full text of DOI:10.2478/s11532-009-0124-x

Cent. Eur. J. Chem. • 8(1) • 2010 • 174–181
DOI: 10.2478/s11532-009-0124-x
Central European Journal of Chemistry
Synthesis and characterization of some
chalcones and their cyclohexenone derivatives
Research Article
Thekke V. Sreevidya1, Badiadka Narayana1*, Hemmige S. Yathirajan2
1 Department of Post-Graduate Studies and Research in Chemistry, Mangalore
University, Mangalagangotri 574 199, INDIA
2 Department of Studies in Chemistry,
University of Mysore, Mysore 570 006, INDIA
Received 27 February 2009; Accepted 18 August 2009
Abstract: A series of chalcones and their derivatives have been synthesized. Chalcones, 1-(1,3-benzodioxol-5-yl)-3-(aryl)-prop-2-en-1-ones
were prepared by the aldol condensation of 1-(1,3-benzodioxol-5-yl)ethanones and aryl aldehydes. Based-catalyzed condensation
of 1-(1,3-benzodioxol-5-yl)-3-(aryl)prop-2-en-1-ones with ethyl acetoacetate yields corresponding ethyl 4-(1,3-benzodioxol-5-yl)-6-
(aryl)-2-oxocyclohex-3-ene-1-carboxylates. Some of the synthesized chalcones were reported in the literature; the newly synthesized
compounds were characterized by single crystal X-ray studies, IR, 1H-NMR and LCMS mass spectral analysis.
Keywords: Chalcones • Michael addition • Single crystal XRD • Cyclohexenones
© Versita Warsaw and Springer-Verlag Berlin Heidelberg.
1. Introduction
sclerosis patients and are thus useful in controlling the
progressive nature of the disease [16]. Apart from being
Chalcones, one of the major classes of natural products
with widespread occurrence in fruits, vegetables,
spices, tea and soy-based foodstuff, have been
recently the subject of extensive investigations due to
their interesting pharmacological activities. Chemically
they consist of open-chain flavonoids in which the
two aromatic rings are joined by a three-carbon α,β-
unsaturated carbonyl system. It is a unique template
molecule that is associated with several biological
activities. The radical quenching properties of the
phenolic groups present in many chalcones have raised
interest in the use of the compounds or chalcone-rich
plant extracts as either drugs or food preservatives [1].
Chalcones have been reported to possess many useful
properties, including anti-inflammatory [2], antifungal
[3-5], antioxidant [6], cytotoxic [7] and anticancer [8-11]
activities. Certain chalcone derivatives are reported to
inhibit the polymerization of tubulin to form microtubules
and can be used as antimitotic agents [12-15]. Chalcone
derivatives are also known to inhibit the destruction of
myelin sheath in the central nervous system of multiple
biologically important compounds, chalcone derivatives
show non-linear optical (NLO) properties with excellent
blue light transmittance and good crystallizability. Not
only photonics deals with the synergy between optics
and electronics, it also provides the ties between optical
materials, devices and systems. The inventions of
lasers and nonlinear optical phenomena (NLO) have
opened up many new areas of devices and systems,
like frequency conversion and optical switching, that are
of practical interest to mankind [17]. The NLO effect in
the organic molecules originates from a strong donor-
acceptor intermolecular interaction,
a delocalized
π-electron system, and is also due to the ability to
crystallize in non-centrosymmetric manner. Organic
NLO materials are attracting a great deal of interest as
they have greater optical susceptibilities, and higher
optical thresholds for laser power compared to inorganic
materials, as well as inherent ultrafast response times
[18]. It is widely accepted that the NLO response is
greatly increased upon lengthening of the chain of the
conjugated π-bridge and chalcone derivatives have
* E-mail: nbadiadka@yahoo.co.uk
174

T.V. Sreevidya, B. Narayana, H. S. Yathirajan
such a configuration, with two planar rings connected by was filtered off and washed with cold methanol.
a conjugated double bond and hence, show significant Recrystallization from methanol yielded the pure
nonlinearity [19].
compounds with 62-89% yields.
Many chalcones have been reported as having high
Synthesis of chalcones can also be carried out using
antimalarial activity, probably as a result of Michael LiOH as a dual activation catalyst [25].
addition of nucleophilic species to the double bond of the
enone [20,21]. Licochalcone A, isolated from Chinese
2.2. General procedure for the synthesis of
ethyl 4-(1, 3-benzodioxol-5-yl)-2-oxo- 6-(aryl)
cyclohex-3-ene-1-carboxylate (5a-i)
liquorice roots, has been reported as highly effective in
chloroquine resistant Plasmodium falciparum strains in
a [3H] hypoxanthine uptake assay [22,23].
Chalcones and ethyl acetoacetate in the 1:1 ratio were
refluxed in 15 mL of ethanol for 2 h in the presence of
0.5 mL 10% KOH. The reaction mixture was kept
overnight at room temperature. The precipitate was
filtered off and recrystallized from ethanol to yield the
required material, as an isomeric mixture, with 58-78%
yield.
Michael addition reactions of chalcones and
azachalcones with ethyl acetoacetate have been
successfully performed in the presence of catalytic
amount of K2CO3 and under high speed vibration milling
conditions [24]. The reactions took place at ambient
temperature, without any solvent, and were completed
within a very short time. In most cases, conventional side
reactions were avoided and thus high chemoselectivity
and quantitative yields were achieved. The desired
Michael adducts obtained consisted exclusively
of two diastereomers, ‘anti’ and ‘syn’, which were
determined and assigned by 1H-NMR spectroscopy.
Herein, we discuss the synthesis and characterization
of two series of organic compounds, viz., chalcones
and their cyclohexenone derivatives. Some of the
chalcones were already reported in literature [25-28].
The newly synthesized compounds were characterized
2.3. Spectral data
2.3.1. Ethyl 4-(1,3-benzodioxol-5-yl)-6-(4-lorophenyl)-
2-oxocyclohex-3-ene-1-carboxylate (5a)
IR (KBr, cm-1): 1664 cm-1 (νc=o ketone), 1735 cm-1 (νc=o
1
ester); H-NMR (300 MHz): δ 1.06 (t, 3H, CH3), 2.56-
2.70 (m, 2H, -CH-CH-Ar), 3.23-3.41(m, 2H, CH2-CH-
Ar), 4.07- 4.14 (q, 2H, -OCH2), 6.05 (s, 2H, -OCH2O),
6.32 (s,1H, =CH), 6.89 (m, 3H, ArH), 7.31 (m, 4H, ArH);
LCMS: 399 (M+1), 400 (M+2).
1
by elemental, IR, H-NMR and LCMS mass spectral
2.3.2. Ethyl 4-(1,3-benzodioxol-5-yl)-6-(3,4-
dimethoxyphenyl)-2-oxocyclohex-3-ene-1-carboxylate
(5b)
analysis; a few chalcones were characterized using
single crystal XRD.
IR (KBr, cm-1): 1656 cm-1 (νc=o ketone), 1735 cm-1
(νc=o ester); 1H-NMR (300 MHz): δ 1.14 (t, 3H,
CH3), 2.82-3.12 (m, 2H, -CH-CH-Ar), 3.56-3.68 (m,
2H, CH2-CH-Ar), 3.79 (s, 3H, OCH3), 3.82 (s, 3H,
OCH3), 4.10- 4.16 (q, 2H, -OCH2), 6.08 (s, 2H,
-OCH2O), 6.42 (s,1H, =CH), 6.74(d, 1H, ArH), 6.82
(m, 2H, ArH), 7.12 (m, 3H, ArH); LCMS: 425 (M+1),
426 (M+2).
2. Experimental procedure
Melting points were taken in open capillary tubes and
are uncorrected. The purity of the compounds was
confirmed by thin layer chromatography using Merck
silica gel 60 F254 coated aluminium plates in petroleum
ether/ethyl acetate medium. IR spectra were recorded
on Shimadzu- FTIR Infrared spectrometer in KBr (νmax
1
in cm-1). H NMR spectra were recorded in CDCl3 on a
2.3.3. Ethyl 4-(1,3-benzodioxol-5-yl)-6-(3-
bromophenyl)-2-oxocyclohex-3-ene-1-carboxylate (5c)
IR (KBr, cm-1): 1663 cm-1 (νc=o ketone), 1733 cm-1 (νc=o
Bruker (300 MHz) spectrometer using TMS as internal
standard and mass spectra were recorded in LC/MSD
Trap XCT spectrometer.
1
ester); H-NMR (300 MHz): δ 1.10 (t, 3H, CH3), 2.86-
3.10 (m, 2H, -CH-CH-Ar ), 3.71-3.82 (m, 2H, CH2-CH-
Ar), 4.07- 4.14 (q, 2H, -OCH2), 6.04 (s, 2H, -OCH2O),
6.49 (d,1H, ArH), 6.86 (d, 1H, ArH), 7.05 (d, 1H, ArH),
2.1. General procedure for the synthesis of
chalcones (3a-n)
3’,4’-Methylenedioxyacetophenone (0.01 mol) and 7.12 (m,1H, ArH), 7.26 (m, 2H, ArH), 7.44 (m, 1H, ArH),
substituted aryl aldehydes (0.01 mol) were dissolved in 7.49 (s,1H, =CH); LCMS: 445 (M+1), 446 (M+2).
methanol (25 mL) and 5 mL of 10% KOH solution was
slowly added to it under stirring at 15-20°C. Stirring 2.3.4. Ethyl 4-(1,3-benzodioxol-5-yl)-6-(2-
continued for 2 h at the same temperature. Progress methoxynaphthalen-6-yl)-2-oxocyclohex-3-ene-1-
of the reaction was monitored by TLC. The precipitate carboxylate (5d)
175
175

Synthesis and characterization of some chalcones
and their cyclohexenone derivatives
IR (KBr, cm-1): 1658 cm-1 (νc=o ketone), 1737 cm-1 (νc=o ester); aryl aldehydes. The reaction of chalcones with ethyl
1H-NMR (300 MHz): δ 1.06 (t, 3H, CH3), 2.82-3.11 (m, 2H, acetoacetateisknowntoleadtothreestructurallydiverse
-CH-CH-Ar ), 3.75-3.80 (m, 2H, CH2-CH-Ar), 3.86(s, 3H, types of compounds, depending on the experimental
OCH3), 4.03- 4.10 (q, 2H, -OCH2), 6.08 (s, 2H, -OCH2O), conditions.Thecatalystplaysamajorroleindirectingthe
6.39 (s,1H, =CH), 6.82 (dd, 2H, ArH), 6.86 (d, 1H, ArH), reaction towards different end products. A strong Lewis
7.44 (m, 6H, ArH); LCMS: 445 (M+1), 446 (M+2).
acid such as BF3.etherate generates pyrylium cations
during the reaction of chalcones and acetoacetic esters,
2.3.5. Ethyl 4-(1,3-benzodioxol-5-yl)-6-(3-nitrophenyl)- but basic catalyst would turn the intermediate Michael
2-oxocyclohex-3-ene-1- carboxylate (5e)
addition product into cyclohexenones through the
IR (KBr, cm-1): 1660 cm-1 (νc=o ketone), 1733 cm-1 (νc=o intramolecular cyclocondensation of the methyl group,
1
ester); H-NMR (300 MHz): δ 1.12 (t, 3H, CH3), 2.92- originating from acetoacetic acid ester, and the ketone
3.15 (m, 2H, -CH-CH-Ar ), 3.73-3.81 (m, 2H, CH2-CH- function of the chalcone. Thus in the presence of a base,
Ar), 4.07- 4.16 (q, 2H, -OCH2), 6.08 (s, 2H, -OCH2O), chalcones containing 1,3-benzodioxolyl (3a-n) react
6.51 (s,1H, =CH), 6.86 (m, 3H, ArH),7.25 (m, 2H, ArH), with ethyl acetoacetate (4) to produce cyclohexenones
7.62 (m, 2H, ArH); LCMS: 406 (M+1), 407 (M+2).
(5a-i) by means of an intermediate Michael adduct, as
given in Scheme 1. 1-(1,3-Benzodioxol-5-yl)-3-(aryl)
2.3.6. Ethyl 4,6-bis(1,3-benzodioxol-5-yl)-2- prop-2-en-1-ones (3a-n) were prepared by the reaction
oxocyclohex-3-ene-1-carboxylate (5f)
of 1-(1,3-benzodioxol-5-yl)ethanones (1) with aromatic
IR (KBr, cm-1): 1658 cm-1 (νc=o ketone), 1729 cm-1 (νc=o aldehydes (2) in presence of KOH in ethanol as given
1
ester); H-NMR (300 MHz): δ 1.05 (t, 3H, CH3), 2.82- in Scheme 1. The newly synthesized chalcones were
3.07 (m, 2H, -CH-CH-Ar), 3.66-3.77 (m, 2H, CH2-CH- characterized by elemental and X-ray analysis. Some
Ar), 4.03- 4.10 (q, 2H, -OCH2), 6.04 (s, 2H, -OCH2O), of the synthesized chalcones were already reported
5.97 (s, 2H, -OCH2O), 6.48 (d,1H, ArH), 6.79 (d, 1H, in literature as being synthesized in the presence of
ArH), 6.83 (d,1H, ArH), 6.86 (s, 1H, =CH ), 7.05 (d, 1H, LiOH in methanol. In both, the reported and proposed
ArH), 7.09 (d, 1H, ArH), 7.12 (d, 1H, ArH); LCMS: 409 method, the yields were higher than 70%; it seemed that
(M+1), 410 (M+2).
the presence of LiOH increased the rate of the reaction.
A much shorter reaction time and lack of an extraction
2.3.7. Ethyl 4-(1,3-benzodioxol-5-yl)-6-(2- step are the advantages of our procedure over the one
bromophenyl)-2-oxocyclohex-3-ene-1-carboxylate (5g) reported in literature [25].
IR (KBr, cm-1): 1664 cm-1 (νc=o ketone), 1737 cm-1 (νc=o
Thus 1-(1,3-benzodioxol-5-yl)-3-(aryl)prop-2-en-1-
1
ester); H-NMR (300 MHz): δ 1.10 (t, 3H, CH3), 2.86- ones formed on treatment with ethyl acetoacetate in
3.12 (m, 2H, -CH-CH-Ar ), 3.73-3.81 (m, 2H, CH2-CH- presence of KOH in ethanol yield Michael addition
Ar), 4.07- 4.14 (q, 2H, -OCH2), 6.06 (s, 2H, -OCH2O), product. The intermediate formed on cyclization gave
6.49 (d, 1H, ArH), 6.79 (d, 1H, ArH), 7.08 (d, 1H, ArH), ethyl 4-(1,3-benzodioxol-5-yl)-2-oxo-6-(aryl)cyclohex-3-
7.16 (m, 1H, ArH), 7.41 (m, 3H, ArH), 7.48 (s,1H, =CH); ene-1-carboxylate. This cyclization proceeds through
LCMS: 445 (M+1), 446 (M+2).
the intramolecular condensation of a methyl group and
a carbonyl group. The cyclocondensation of ethyl
2.3.8. Ethyl 4-(1,3-benzodioxol-5-yl)-2-oxo-6- acetoacetate with chalcones leads to the generation of
phenylcyclohex-3-ene-1-carboxylate (5i)
two chirality centers in the structure of cyclohexenones
IR (KBr, cm-1): 1663 cm-1 (νc=o ketone), 1737 cm-1 (νc=o and both, R and S, configurations of the chiral carbon
1
ester); H-NMR (300 MHz): δ 1.05 (t, 3H, CH3), 2.76- atoms are expected a mixture of diastereomers will
3.11(m, 2H, -CH-CH-Ar), 3.76-3.81(m, 2H, CH2-CH-Ar), result. No attempt has been undertaken to separate the
4.03- 4.10 (q, 2H, -OCH2), 6.04 (s, 2H, -OCH2O), 6.50 diastereomeric cyclohexenones and they have been
(d, 1H, ArH), 6.86 (d,1H, ArH), 7.12 (dd, 2H, ArH), 7.32 characterized as a mixture. The newly synthesized
(m,5H, ArH), 7.37 (s,1H, =CH); LCMS: 365 (M+1), 366 compounds have been characterized by elemental, IR,
(M+2).
1H-NMR and mass spectral analysis. The spectral data
are reported in the experimental section and elemental
analysis data are given in Tables 1 and 2. The structures
of some chalcones viz., (2E)-1-(1,3-benzodioxol-5-yl)-
3-(4-chlorophenyl)prop-2-en-1-one(I),(2E)-1-(1,3-
benzodioxol-5-yl)-3-(3,4-dimethoxyphenyl)prop-2-en-1-
one (II) and (2E)-1-(1,3-benzodioxol-5-yl)-3-(3-
3. Results and Discussion
Chalcones
catalyzed
were
Claisen–Schmidt
synthesized
by
a
base-
of
condensation
3’,4’-methylenedioxyacetophenone and substituted
176

T.V. Sreevidya, B. Narayana, H. S. Yathirajan
Table 1. Characterization Data of 1-(1,3-Benzodioxol-5-yl)-3-(aryl)prop-2-en-1-ones
O
O
Ar
O
Elemental Analysis, %
Found (Calculated)
Melting
Point
ºC
Compound
No.
Yield*
(%)
Molecular
Formula
Nature of
Products
Ar
C
H
N
Cream
powder
67.14
(67.03)
3.60
(3.87)
3a
68
162-166
C16H11ClO3
-
Cl
White
powder
69.20
(69.22)
5.00
(5.16)
3b
3c
3d
70
66
82
132-134
147-149
161-163
C18H16O5
C17H14O4
C17H12O5
-
-
-
H3CO
OCH3
White
powder
72.20
(72.33)
4.98
(5.00)
H3CO
O
Cream
crystals
68.78
(68.92)
3.99
(4.08)
O
Yellow
powder
81.89
(81.80)
5.00
(4.58)
3e
3f
62
78
122-124
139-141
C24H16O3
C16H12O3
-
-
Cream
crystals
76.04
(76.18)
4.52
(4.79)
Yellow
powder
73.12
(73.20)
5.68
(5.80)
4.81
(4.74)
H3C
3g
3h
3i
75
56
62
74
77
92-94
C18H17NO3
C16H11NO5
C16H11NO5
C17H14O5
N
CH3
Yellow
crystals
64.61
(64.65)
3.52
(3.73)
4.68
(4.71)
131-133
144-146
101-103
120-122
N O 2
Yellow
crystals
64.56
(64.65)
370
(3.73)
4.66
(4.71)
N O 2
Off-white
powder
68.38
(68.45)
4.70
(4.73)
-
-
3j
HO
OCH3
Brownish
powder
57.96
(58.03)
3.42
(3.35)
3k
C16H11BrO3
Br
Brownish
powder
58.12
(58.03)
3.47
(3.35)
-
-
3l
69
65
117-119
124-126
C16H11BrO3
Br
Cream
powder
75.68
(75.89)
4.66
(4.85)
3m
C21H16O4
H3CO
Off -white
powder
71.04
(71.11)
4.16
(4.10)
-
3n
78
118-120
C16H11FO3
F
177
177

Synthesis and characterization of some chalcones
and their cyclohexenone derivatives
Table 2. Characterization Data of (Ethyl 4-(1,3-benzodioxol-5-yl)-2-oxo-6-(aryl)cyclohex-3-ene-1-carboxylate)
O
COOC2H5
Ar
O
O
Elemental Analysis, %
Found (Calculated)
Compound
No.
Yield*
(%)
Melting
Point ºC
Molecular
Formula
Nature of
Products
Ar
C
H
N
66.12
(66.25)
4.72
(4.80)
5a
5b
78
62
135-137
132-134
C22H19ClO5
C24H24O7
Cream powder
Yellow powder
-
Cl
67.60
(67.91)
5.62
(5.70)
H3CO
-
-
OCH3
59.45
(59.61)
4.90
(4.32)
5c
5d
80
76
126-128
116-118
C22H19BrO5
C27H24O6
Cream powder
Cream powder
Br
73.00
(72.96)
5.14
(5.44)
-
H3CO
Yellow
powder
64.17
(64.54)
4.85
(4.68)
3.91
(3.42)
5e
5f
64
85
77
151-153
170-172
121-123
C22H19NO7
C23H20O7
N O 2
O
O
Off white
powder
67.70
(67.64)
5.00
(4.94)
-
-
59.48
(59.61)
4.55
(4.32)
5g
C22H19BrO5
Cream powder
Br
Yellowish
powder
70.52
(70.74)
6.04
(6.18)
3.40
(3.44)
H3C
5h
5i
65
79
86-88
C24H25NO5
N
CH3
Off-white
powder
72.23
(72.51)
5.25
(5.53)
155-157
C22H20O5
-
bromophenyl)prop-2-en-1-one (III) were confirmed by
single crystal X-ray study [29,30] and are given in Figs.
1, 2 and 3. The compound, (2E)-1-(1,3-benzodioxol-5-
yl)-3-(4-chlorophenyl)prop-2-en-1-one (I), crystallizes in
the monoclinic P21/c space group with cell parameters,
a=2.7231(15), b = 4.9239(4), c = 11.9995(7)Å, β= 99.953(6)˚.
The compound, (2E)-1-(1,3-benzodioxol-5-yl)-3-(3,4-
dimethoxyphenyl)prop-2-en-1-one (II), crystallizes
in the triclinic crystal system, space group P1 with
a = 8.2961(2) Å, b = 13.8829(6) Å, c = 14.6713(7)Å,
α = 64.185(4), β = 83.560(3)˚, γ = 84.966(3)˚ and in
(2E)-1-(1,3-benzodioxol-5-yl)-3-(3-bromophenyl)prop-
2-en-1-one (III), the molecule adopts an E configuration
with respect to the C=C double bond of the propenone
unit and crystallizes in monoclinic, P21/c, a = 14.237(3)
Å, b = 8.1811 (17) Å, c=11.717(2) Å, β= 100.658(3)°.
The 13 non-H atoms of the benzodioxol and propenone
units in III are approximately coplanar and the
bromobenzene ring plane forms a dihedral angle of
10.8(1)° to this plane. The structure is layered, with the
molecules forming a herring-bone arrangement within
each layer.
178

T.V. Sreevidya, B. Narayana, H. S. Yathirajan
(b)
(a)
Figure 1. Ortep drawings (a) and molecular packing (b) for (2E)-1-(1,3-benzodioxol-5-yl)-3-(4- chlorophenyl)prop-2-en-1-one
(c)
(d)
Figure 2. Ortep drawings (c) and molecular packing (d) for (2E)-1-(1,3-benzodioxol-5-yl)-3-(3,4-dimethoxyphenyl)prop-2-en-1-one
(f)
(e)
Figure 3. Ortep drawings (e) and molecular packing (f) for (2E)-1-(1,3-benzodioxol-5-yl)-3-(3- bromophenyl)prop-2-en-1-one
179
179

Synthesis and characterization of some chalcones
and their cyclohexenone derivatives
O
O
O
O
O
H
CH3
O
Ar
Base
EtOH
Ar
+
O
(3a-n)
2
1
COOC2H5
H3C
Base
4
O
O
O
H3C
COOC2H5
Ar
COOC2H5
Ar
*
*
O
O
O
O
O
(5a-i)
Scheme 1. Claisen–Schmidt condensation of 3’,4’-methylenedioxyacetophenone and substituted aryl aldehydes
Hydrogen bonding and crystal packing effects
influence the twist angle between the mean planes of
4. Conclusions
the 1,3-benzodioxol-5yl and benzene groups in both
Some chalcones, such as 1-(1,3-benzodioxol-5-
yl)-3-(aryl)prop-2-en-1-ones, and their cyclized
products with ethyl acetoacetate, such ethyl
4-(1,3-benzodioxol-5-yl)-2-oxo-6-(aryl)cyclohex-3-
ene-1-carboxylate derivatives, were synthesized
and characterized by spectral analysis.
I and II, while π-π stacking interactions between the
adjacent 5-membered dioxol rings and the 9-membered
benzodioxol group, as well as the benzyl ring, stabilize
the crystal packing. In I there is an intermolecular
C–H·O hydrogen bond between the C15 and O1
atoms. The dihedral angle between the mean planes
of the 1,3-benzodioxol-5-yl group and the benzene
ring is 18.26°. In II the compound crystallizes with
two independent molecules in the asymmetric unit.
Intermolecular C–H-O hydrogen bond interactions
occur in both molecules that help to stabilize the crystal
packing in the unit cell. The dihedral angle between the
mean planes of the 1,3-benzodioxol-5-yl group and the
benzene ring in the two independent molecules in II is
7.8(9)° (A) and 37.9(7)° (B), respectively. The molecular
packing in I and II is stabilized by hydrogen bonding and
also by π-π stacking interactions.
Acknowledgements
One of the author (TVS) thanks Mangalore University
for the use of the research facilities and DST & UGC,
Govt. of India, for financial support through FIST & SAP
programmes.
180

T.V. Sreevidya, B. Narayana, H. S. Yathirajan
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